The Characteristics of Electricity The

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Lightning flashes around transmission lines carrying electricity to communities.

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Contents

10

Static charges collect on surfaces and remain there until given a path to escape.

10.1

Exploring the Nature of Static Electricity

10.2

The Transfer of Static Electric Charges DI

10.3

Electrostatics in Our Lives

11

Current electricity is the continuous flow of electrons in a closed circuit.

11.1

Current, Potential Difference, and Resistance

11.2

Series Circuits and Parallel Circuits

11.3

Ohm’s Law DI

12

We can reduce our electrical energy consumption and use renewable energy resources to produce electrical energy.

12.1

Renewable and Non-Renewable Energy

Resources for Generating Electricity

12.2

Reducing Our Electrical Energy Consumption DI

Unit Task

In your Unit Task, you will evaluate methods of local electricity generation that could be used as backup sources for the regional power grid. Your investigations into the characteristics of electricity, methods of conserving electrical energy, and methods of providing electrical energy will help prepare you for your task.

Essential Question

How can we use local resources to generate electricity in a dependable, environmentally friendly way?

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Exploring

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Toronto was one of many cities that were without electricity during the 2003 blackout.

Some places in Ontario now celebrate Blackout Day on August 14 to remind people of how important it is to conserve energy.

Electrical generating stations from Ohio to Ontario shut down, leaving

50 million people in the dark. Why?

Blackout!

Imagine what it would be like to live in a world without electricity. Now, count to nine. In a mere nine seconds, that scenario came true. On August 14, 2003, at 4:11 in the afternoon,

50 million people in Ontario and the northeastern United States were plunged into the largest electrical blackout in North

American history. Elevators stuck between floors, subways were in blackness, traffic lights stopped working, and television screens and computer monitors went dark.

Electricity is often generated far from cities and is distributed along a network that includes electrical generating stations, transmission lines, and distribution stations. This huge, interconnected system of electricity networks is called the

“energy grid.” Ontario, New York, Michigan, and other northeastern provinces and states are part of the eastern interconnection grid.

Electricity cannot be stored for long after it is generated, so all parts of the grid must maintain a balance of supply and demand.

If a transmission line or generator is overloaded, that part of the

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Home Quit energy grid is disconnected automatically and the electricity is sent along alternative paths. One cause of problems in an energy grid is transmission lines that touch trees so that the electricity moves through the trees into the ground instead of along the wire.

Preventing Future Blackouts

On August 14, a series of events, including human error, high demand, lines touching trees, automatic shutdowns, and failures of alarm systems, resulted in a huge surge of electricity in the grid. Within seconds, 256 electrical generating stations from Ohio to New York to Ontario shut down as a protective control. It took almost two full days to get all the generating stations back in operation and electricity restored to all the affected areas.

This blackout raised difficult questions that could only be solved by government and electrical industry experts from both

Canada and the United States working together. How did the blackout happen? What can be done to prevent such a blackout from occurring again? These are very complex questions to investigate.

By working cooperatively, groups from the two countries successfully figured out the answers to these questions. Now, because of their hard work, the electrical grid is safer and better able to deal with a similar situation. Smaller, local blackouts do occur from time to time. But the knowledge learned from the mistakes of previous large blackouts helps reduce the chances of such a large-scale blackout happening again.

A transmission line is automatically disconnected from the grid when it touches treetops or other objects.

D1 STSE Science, Technology, Society, and the Environment

Electricity Concept Map

Electrical energy is often in the news. You have probably read or viewed reports about the costs and benefits of producing energy from renewable and non-renewable sources. You might be practising some ways to reduce electrical energy consumption and achieve electrical savings in your home. And you can probably describe the importance of electricity to your daily life.

Now is your opportunity to get a sense of how your pieces of knowledge about electricity fit together.

1.

As a class, create a concept map about electricity. Start with the word “electricity” in the centre of a large piece of chart paper.

2.

Add categories, terms, concepts, and sketches to the map, making links between the parts that are connected.

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Static charges collect on surfaces and remain there until given a path to escape.


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Sparks flash from the centre of a plasma ball to the point of contact where a hand touches the ball.

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Skills You Will Use

In this chapter, you will:

• investigate the transfer of static electric charges by friction, contact, and induction

• predict the ability of different materials to hold or transfer electric charges

• plan and carry out inquiries to determine and compare the conductivity of various materials

• apply knowledge and understanding of the safe operation of electrical equipment

Concepts You Will Learn


• learn about the differences between electrical insulators and conductors

• explain how materials allow static charges to build up or to discharge

• analyze the design of technological devices that improve electrical efficiency or protect other devices by using or controlling static electricity

Why It Is Important

Static electricity is part of our daily lives. By understanding how charges build up and discharge, we can avoid problems caused by sparks and make use of static electricity to improve our lives.

Before Reading

Determining Importance

Preview the subheadings and illustrations in Chapter 10.

Which topics and illustrations are familiar? Which topics and illustrations are unfamiliar based on your background knowledge and experience? The unfamiliar topics and illustrations represent the information that is most important for you to learn. Create a list of learning goals for this chapter based on the information that represents new learning for you.

Key Terms

• conduction • conductor • electrical discharge

• electron • electron affinity • friction • induction

• insulator • static electricity

Static charges collect on surfaces and remain there until given a path to escape.

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10.1

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Exploring the Nature of Static Electricity

Here is a summary of what you will learn in this section:

• Solid materials are charged by the transfer of electrons.

• When an atom gains electrons, it becomes negatively charged.

• When an atom loses electrons, it becomes positively charged.

• Electrons can be removed from objects through friction.

• Particles with unlike charges attract each other, and particles with like charges repel each other.

• Electrical insulators and conductors are materials categorized by how freely they allow electrons to move.

Figure 10.1 Electric charges cause strands of hair to repel each other and be attracted to the balloon.

A Shocking Experience

On a cold winter day, you have probably pulled a sweater off over your head or removed your hat and felt your hair flying up. Or maybe you have reached to touch a doorknob or the door handle of a car and received an electric shock. These examples and hairraising experiences like the one in Figure 10.1 are caused by electric charges . Electric charges are charged particles that exert an electric force on each other. These charged particles are very small. In fact, there are millions of them on each standing hair in the picture above.

The accumulation or gathering of even larger numbers of electric charges can lead to some impressive electrical displays.

Think back to the last time you observed a lightning storm. The large, bright flashes of lightning look like the small electric sparks you may have seen when touching the doorknob or taking off your sweater. In fact, they are the same thing, just different in size. These are all examples of static electricity.


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D2 Quick Lab

Characteristics of Electric Charge

A characteristic is a distinguishing trait or quality of a substance or object.

Purpose

To observe the characteristics of electric charge

Materials & Equipment

• confetti or gelatin powder

• plastic drinking straw

• 2 balloons

• Van de Graaff generator

• thin paper strips

• clear adhesive tape

• 3 aluminum pie plates

• clear plastic cup with lid

• polystyrene “popcorn”

• metal rod and lab stand

Procedure

1.

Read through the procedure steps, and make predictions about what you think will happen in each step. Record your predictions.

2.

Sprinkle some confetti or gelatin powder in a small area on your desk. Push a plastic drinking straw through your hair several times, and bring it close to the confetti or gelatin powder. Record your observations.

3.

Inflate two balloons, and knot the ends. Rub one side of each balloon on your hair or clothing.

Hold the balloons by the knots, and bring the rubbed surfaces slowly together. Observe the results.

4.

Turn one balloon so that its rubbed surface faces away from the other balloon. Again bring the balloons together. Record your observations for steps 3 and 4.

5.

If your classroom has a Van de Graaff generator, your teacher will demonstrate the following experiments by putting the materials for each experiment in place and then turning on the generator. Record your observations for each experiment.

(a) Tape one end of the thin paper strips to the

Van de Graaff generator.

(b) Place a stack of three aluminum pie plates on the Van de Graaff generator.

(c) Place a clear plastic cup full of polystyrene

“popcorn” on the Van de Graaff generator.

Put a loose-fitting lid on top of the cup.

(d) Attach a metal rod to a lab stand, and place it close to the Van de Graaff generator.

6.

Return everything you used to the areas designated by your teacher.

Questions

7.

(a) Which objects were attracted to each other?

(b) Which objects were repelled or pushed away from each other?

8.

How did your observations compare with your predictions for each step?

9.

What do you think caused the movements that you observed?


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Electrically Charged Particles

You may recall from earlier studies that an element is a pure substance that cannot be broken down into simpler substances. An element is made up of tiny particles called atoms. An atom is the smallest part of an element with the element’s properties. Within an atom, there are three types of smaller particles: protons, neutrons, and electrons. Protons and electrons are electrically charged particles. Protons have a positive electric charge (+), and electrons have a negative electric charge (–). Neutrons have no electric charge, so they are neutral. The protons and neutrons are in the nucleus at the centre of the atom. The electrons are outside the nucleus (Figure 10.2).

Although they contain electrically charged particles, atoms are neutral. The number of protons in the nucleus equals the number of electrons around the nucleus, so the number of positive and negative charges is equal. This makes an atom neutral.

neutron proton nucleus electron

W O R D S M AT T E R

“Static” is from the Greek word statikos, meaning causing to stand.

The word “stationary,” which means not moving, is based on the same

Greek word.

Figure 10.2

Each atom is made up of protons and neutrons inside the nucleus and electrons in the area around the nucleus.

Static Charges

Objects can become charged when electrons move from one object to another. The electric charge that builds up on the surface of the object is called a static charge or static electricity . The charges are “static” because they remain very nearly fixed in one location on the surface of the object until they are given a path to escape.

An object that has more electrons than protons is negatively charged. An object that has more protons than electrons is positively charged. You can group objects according to three kinds of charge: positive, negative, and neutral. If a neutral object obtains extra electrons, the object becomes negatively charged. If a neutral object loses electrons, the object becomes positively charged.


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Friction and the Movement of Electrons

All solid materials are charged by the transfer of electrons. How do atoms lose or gain electrons to become electrically charged?

One common cause of electron transfer is friction, which occurs when objects rub against each other.

Friction is the force resisting the relative motion of two surfaces in contact. When two objects rub together, the force of friction can remove electrons from one object and cause them to transfer to the other object. As one object loses electrons, the other object gains them, as shown by the amber and fur in

Figure 10.4.

If you count the electrons in Figure 10.4, you will notice that no electrons are lost during the process of charging. They are simply transferred. The position of the positive charges does not change during the process of charging.


“Electricity” comes from the Greek word elektron, meaning amber, which is fossilized tree resin (Figure 10.3).

Amber has been used for thousands of years to study static electricity.

Figure 10.3

Amber is fossilized tree resin. This piece of amber contains bugs that were living on the tree and got caught in the amber.

electrons neutral neutral negative positive

(a) (b) (c)

Figure 10.4

The amber and the fur are electrically neutral (a). If you rub the amber with the fur, electrons transfer from the fur to the amber (b). As a result, the fur becomes positively charged and the amber becomes negatively charged (c).

It’s important to remember that the transfer of the charges from one object to another is possible because the two objects are rubbing against each other. Both objects are neutral before they are rubbed together. They become charged as a result of the rubbing.

For any charging procedure, it’s important to keep in mind that new electric charges are not being created. The electrons in each object are just being rearranged within the object or transferred to another object.


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Suggested Activity •

D3 Inquiry Activity on page 402

Electron Affinity

Table 10.1

A Triboelectric Series

Different substances have different abilities to hold on to electrons.

The tendency of a substance to hold on to the electrons is called electron affinity .

Table 10.1 lists a series of selected materials in order of their electron affinity. You will

Tend to lose electrons

(+) human hands (dry) glass human hair nylon cat fur silk notice that the higher the material is in the list, the greater the tendency for that material to lose electrons. cotton steel wood amber

This means that if you rub together two materials listed in the table, you can determine which material will be positively

Tend to gain electrons ebonite plastic wrap

Teflon® charged and which material will be negatively charged. For

(–) example, if you rub nylon and steel together, the nylon will become positive and the steel will become negative. The nylon will lose electrons, because it is higher in the table. The electrons from the nylon are transferred to the steel, making the steel negative.

This table is referred to as a “triboelectric” series. The term comes from tribos , a Greek word meaning to rub.

Note that there can be a slightly different order for materials such as fur or wood depending on which type of animal the fur is from and which type of tree the wood is from.

Learning Checkpoint

1.

Where are electrons in the atom?

2.

What does “static” mean in “static electricity”?

3.

What happens when two objects made out of different materials are rubbed together?

4.

What term describes an atom’s tendency to hold on to electrons?

5.

In each of the following pairs, state which one is more likely to give up electrons.

(a) wood or human hair

(b) plastic wrap or steel

(c) cotton or silk


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Laws of Attraction and Repulsion

You may have heard the expression “opposites attract” in discussions about people. This is definitely true for electric charges (Figure 10.5). Scientists studying the interaction of objects have observed that when a positively charged object is brought close to a negatively charged object, the two objects attract each other. When two objects with the same charge are placed close together, the objects repel each other.

Opposite charges attract.

During Reading

Visualizing and

Picture Mapping

Good readers use the strategy of visualizing to understand the important details of a large amount of complex information.

One way to visualize is to create a picture map. Using the information about the laws of attraction and repulsion, begin drawing pictures to represent the information provided in this section. Add to your picture map as you read about electrical insulators and conductors.

Figure 10.5

If you increase the amount of charge on objects, the attraction or repulsion also increases.

Like charges repel.

As a result of many scientific investigations, scientists have established the following laws of static electric charges.

• The law of attraction states that particles with opposite charges attract each other.

• The law of repulsion states that particles with like charges repel each other.

Coulombs

Charles-Augustin de Coulomb was a French physicist who worked with electric charges and made several important discoveries (Figure 10.6). He showed that when two charged objects are placed closer together, the attraction or repulsion increases. When the charged objects are moved farther apart, the attraction or repulsion decreases. In his honour, the metric unit for electric charge is named the coulomb (C) . One coulomb equals 6.24 × 10 18 electrons added to or removed from a neutral object.

Figure 10.6

Charles-Augustin de

Coulomb (1736–1806)


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Electrical Insulators and Conductors

Another way to group materials is by their conductivity.

Conductivity is the ability of materials to allow electrons to move freely in them. Materials that hold onto their electrons and do not allow them to move easily are called electrical insulators.

An electrical insulator is a solid, liquid, or gas that resists or blocks the movement of electrons, as shown in Figure 10.7. Dry wood, glass, and plastic are all examples of electrical insulators.

An insulator can hold a static charge because static charges remain nearly fixed in place.

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(a) Insulator: The electrons (–) are bound tightly to the nuclei (+) so they resist movement.

(b) Conductor: The electrons are not as tightly bound to the nuclei. They can move away from the nuclei.

Figure 10.7

Electrons in an insulator cannot move freely. Electrons in a conductor can.

Materials that allow electrons to change positions are called conductors (Figure 10.8). Conduction is the movement or transmission of electrons through a substance. Examples of conductors include the metals copper and aluminum.

Some materials allow only some movement of electrons.

This is the category of materials called fair conductors. In a fair conductor, the electrons do not move as freely as in a conductor, but they are not held almost in place as they are in an insulator.

Figure 10.8

The metal wire in the electric fence allows electrons to move. The plastic insulator resists the movement of electrons.


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Table 10.2 gives some examples of conductors, fair conductors, and insulators. There are variations within each category, as some materials are better or poorer conductors than others.

Table 10.2

Conductivity of Selected Materials

Conductors copper aluminum iron mercury other metals

Fair Conductors water with dissolved minerals moist air human body carbon soil

Insulators rubber wood plastic pure water metal oxides, such as rust

Water as a Conductor

Notice in Table 10.2 that water is an insulator only if it is pure.

However, most water has dissolved minerals in it, so its conductive properties change and it becomes a fair conductor.

This is why you do not want to be in a lake during a thunderstorm. If lightning hits the water, the electric charges from the lightning will spread out through the water and cause you serious or fatal injury. This is also why you should not use water to try to put out an electrical fire (Figure 10.9). You also need to take care not to operate electrical appliances near water or with wet hands.

Figure 10.9

Use an all-purpose fire extinguisher for an electrical fire.


1.

(a) What does the law of attraction state?

(b) What does the law of repulsion state?

2.

What is a coulomb?

3.

Define “electrical insulator.”

4.

What does “conduction” mean?

5.

(a) Name two examples of good conductors.

(b) Name two examples of fair conductors.

(c) Name two examples of insulators.

Take It Further

A Faraday cage is an enclosure made of conducting material that protects its contents from electric charges. Find out how airplanes, cars, and even some specially designed clothes can act as

Faraday cages. Start your research at ScienceSource .


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D3 Inquiry Activity

Investigating Static Electricity

Question

What is the effect of charged objects on each other and on neutral objects?


• 2 vinyl strips • beaker


• ring stand

• paper towel

• 2 acetate strips

• watch glass

• wooden ruler or metre stick

Skills Reference 2

SKILLS YOU WILL USE

Adapting or extending procedures

Drawing conclusions

4.

Bring one of the charged vinyl strips close to the suspended acetate strip. Make sure the two strips do not touch each other. Record your observations.

5.

Place the beaker upside down on the desk or table. Place the watch glass on top of the beaker as shown in Figure 10.10. Balance the ruler so it is lying flat and centred on the watch glass. Bring a charged vinyl strip near, but not touching, one end of the ruler. Record your observations.

Procedure

1.

Copy the following table into your notebook to record your findings. Give your table a title.

Hanging

Object charged vinyl charged acetate charged acetate ruler ruler

Approaching

Object Predictions Observations charged vinyl charged acetate charged vinyl charged vinyl charged acetate

2.

Tape one end of a vinyl strip to the ring stand so the strip hangs down. Rub the hanging vinyl strip with the paper towel to charge it. Then, rub the other vinyl strip with the paper towel, and bring that vinyl strip close to the suspended strip.

Record your observations in your table.

3.

Repeat step 2, using the two acetate strips and the paper towel. Record your observations.

Figure 10.10

Balance the ruler on the watch glass on top of the beaker.

6.

Bring a charged acetate strip near one end of the ruler. Record your observations.

Analyzing and Interpreting

7.

Usually, charged vinyl is negative and charged acetate is positive. How does this information explain your observations?

Skill Practice

8.

Describe how you would modify the procedure in this activity so that you could identify the type of charge on a charged object.

Forming Conclusions

9 . Write three statements that summarize your observations.


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10.1

CHECK and REFLECT

Key Concept Review

1.

(a) Draw a diagram of an atom that has four protons, five neutrons, and four electrons.

(b) Label each particle with its name and whether it is positive (+), negative (–), or neutral.

2.

(a) What is friction?

(b) Explain how friction can be used to transfer electrons. Use two substances from the triboelectric series in Table

10.1 on page 398 in your answer.

3.

Explain why this statement is false: “A neutral object contains no charge.”

4.

State the two laws of static electric charges.

5.

Where are static charges held?

6.

Why might a plastic rod that contains a large number of electrons not have a static charge?

7.

(a) What is the difference between a conductor and an insulator?

(b) What is an example of a conductor?

(c) What is an example of an insulator?

8.

(a) What is the difference between a conductor and a fair conductor?

(b) What is an example of a fair conductor?

9.

Why can you not use water to put out an electrical fire?

Connect Your Understanding

10.

Do two identical objects become statically charged when you rub them together?

Explain why they do or do not.

Quit

11.

Copy this chart into your notebook. For each pair, predict which substance becomes more positively charged and which becomes more negatively charged when the two substances are rubbed together. Use

Table 10.1, A Triboelectric Series on page 398, to help you make predictions.

Charged Pairs

Pairs cotton, steel cotton, silk human hair, human hands (dry)

Becomes More

Positively

Charged

Teflon®, wood glass, plastic wrap

Becomes More

Negatively

Charged

12.

Make a list of five different ways in which you experience static electricity in your own life.

13.

(a) While fishing in an aluminum boat in the middle of a lake, you notice storm clouds forming nearby. Why is it a good idea to get to shore as fast as possible?

(b) Would your answer change if the lake somehow became filled with distilled water with no ions present in it?

Explain why or why not.

Reflection

14.

What are two questions about static electricity that you would like to explore further?

For more questions, go to ScienceSource .


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The Transfer of Static Electric Charges


• Electroscopes are instruments that detect static charge.

• In charging by contact, an orginally neutral substance gains the same charge as the charged object that touched it.

• In charging by induction, an originally neutral substance gains the opposite charge to the charged object.

• Neutral objects are attracted to charged objects.

• Grounding an object transfers electrons between the object and the ground, making the object neutral.

• An electrical discharge occurs when charges are transferred quickly.

Figure 10.11

The bits of paper are attracted to the statically charged comb.

Charged Objects

What does dust on a computer screen have in common with paper on a comb (Figure 10.11)? In both examples, there is attraction between objects with unlike charges. You may have noticed a similar effect when you unpack a box containing polystyrene packing foam and the little pieces of foam stick to your skin and clothes. Polystyrene is very low on the triboelectric series and becomes charged very easily.

How do you know when an object is charged? Rather than testing whether the object sticks to something else, you can use an electroscope , which is an instrument that can detect static charge. The electroscope was first invented in 1748 by a French clergyman and physicist named Jean Nollet.

A metal-leaf electroscope has two very thin metal pieces, called leaves, suspended from a metal rod (Figure 10.12 on the next page). The metal rod is attached to a top plate or metal knob.

When a charge is transferred to the plate or knob, the charges spread out over the whole structure, including the leaves. The greater the charge, the greater the separation between the leaves.

An electroscope is one of the devices that can be used to study static electricity. The study of static electric charges is called electrostatics .


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D4 Quick Lab

Using an Electroscope

Purpose

To determine what happens to an electroscope when different charged objects are brought near it


• plastic comb or straw or ebonite rod

• metal-leaf and/or pith-ball electroscope

• glass, acrylic, or acetate rod

• wool sweater

• silk fabric

Procedure

Part 1 — Metal-Leaf Electroscope

1.

Charge the comb or straw by running it through your hair, or rub an ebonite rod on a wool sweater.

2.

Bring the charged object near, but not touching, the top of the electroscope (Figure 10.12).

Observe the motion of the metal leaves. Then, move the object away and observe the leaves again. Record your observations.

3.

This time, touch the charged object to the top of the electroscope. You can rub the object along the top of the electroscope if necessary. Observe the motion of the metal leaves. Then, move the object away and observe the leaves again.

Record your observations.

4.

Charge the glass, acrylic, or acetate rod by rubbing it with the silk fabric. Repeat steps 2 and 3 using this charged rod.

Part 2 — Pith-Ball Electroscope

5.

Charge the comb or straw by running it through your hair, or rub an ebonite rod on a wool sweater.

6.

Bring the charged object near the pith ball but do not touch it (Figure 10.13). Record your observations.

7.

This time, touch the pith ball with the charged object. Then, touch it again. Record your observations.

8.

Charge the glass, acrylic, or acetate rod by rubbing it with the silk fabric. Repeat steps 6 and 7 using this charged rod.

Questions

9.

What role did friction play in this activity?

10.

With your group, explain what happened in Part

1, using your knowledge about charges. Assume your object had a negative charge placed on it.

11.

With your group, explain what happened in Part

2, using your knowledge about charges. Assume your object had a negative charge placed on it.

Figure 10.12

Metal-leaf electroscope Figure 10.13

Pith-ball electroscope


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Detecting Static Charge

In order to predict what charge is transferred to an electroscope, you can use a standard set of charged objects, such as ebonite and glass. Ebonite is a hard rubber material that is low on the triboelectric series and readily accepts electrons. When ebonite is rubbed with fur, it becomes negative (Figure 10.14). Glass is high on the triboelectric series and tends to give away electrons. When glass is rubbed with silk or plastic, it becomes positive, as shown in

Figure 10.14.


D5 Quick Lab on page 412

Figure 10.14

To test unknown charges, you can use the known charges on an ebonite rod (a) and a glass rod (b).

When a negatively charged rod is brought near a neutral electroscope, the electrons in the electroscope are repelled by the rod. The electrons move down into the leaves of the electroscope.

The leaves are now both negatively charged, so they repel each other and move apart (Figure 10.15). When the negatively charged rod is taken away, the negative charges in the electroscope are no longer repelled, so they move throughout the leaves, stem, and knob. The leaves drop down, and the electroscope is neutral again.

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The leaves are not separated in the neutral electroscope (a). The leaves repel each other when they are charged negatively or positively (b).

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Charging by Contact

As you learned in section 10.1, electrons can be transferred through friction. Electrons can also be transferred through contact and conduction. You can charge a neutral object by contact when you touch it with a charged object. Charging by contact occurs when electrons transfer from the charged object to the neutral object that it touches. The neutral object gains the same type of charge as the object that touched it because the electrons move from one object to the other (Figure 10.16).

During Reading

Understanding Terms and Concepts

A Frayer quadrant can help you understand a term or the concept it represents. Divide a rectangle into four sections, and put the term or concept as the rectangle’s title above it (e.g.,

Charging by Contact). In the top left section, write a definition of the term using your own words and words from the text. In the top right section, write facts related to the term. In the lower left section, write examples of the term from the textbook. In the lower right section, write non-examples of the term.

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Figure 10.16 (a) When a negatively charged object touches a neutral object, electrons move to the neutral object, making it negative.

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(b)

(b) When a positively charged object touches a neutral object, electrons move from the neutral object to the positive object and make the neutral object positive.

Suggested Activities •

• D6 Inquiry Activity on page 413

• D7 Inquiry Activity on page 414

Induction

Induction is the movement of electrons within a substance caused by a nearby charged object, without direct contact between the substance and the object.

If you rub a rubber balloon on your hair, electrons will transfer from your hair to the balloon, making the balloon negative. The charges stay in a nearly fixed, or static, position on the balloon because rubber is an insulator. When you bring the negatively charged balloon near a neutral wall, the negatively charged electrons on the balloon repel the negative charges on the wall, making that part of the wall a positive surface. The balloon is said to induce a charge on the wall because it charges the wall without contacting it (Figure 10.17).

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Figure 10.17

The negatively charged balloon has induced a positive charge on the wall’s surface without touching the wall.


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Charging by Induction

When you charge an object by induction, you use a charged object to induce a charge in a neutral object and then ground the charged object so it retains the charge. This newly charged object has the opposite charge to the charge on the charging object. Grounding is the process of connecting a charged object to Earth’s surface. When you connect a charged object to the ground, you provide a path for charges to travel to or from the ground. Figures 10.18 and 10.19 show the process of charging by induction. Grounding occurs in diagram (b).

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Figure 10.18

(a) When a negatively charged object comes near a neutral electroscope, it repels the electrons in the neutral electroscope.

(b) When you ground the neutral electroscope, you provide its electrons with a path away from the repulsive influence. Some electrons leave the electroscope.

(c) When you remove the ground and the charged object, the electroscope is left with a positive charge because it has lost some electrons.

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Figure 10.19

(a) When a positively charged object comes near a neutral electroscope, it attracts electrons in the neutral electroscope.

(b) When you ground the neutral electroscope, you provide a path for electrons to go toward the positive influence.

(c) When you remove the ground and the charged object, the electroscope is left with a negative charge because extra electrons are trapped on it.

UNIT D The Characteristics of Electricity

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1.

What does an electroscope detect?

2.

In the contact method of charging, what charge does a neutral substance gain compared to the object that touched it?

3.

In induction, what charge does a neutral substance gain compared to the object brought near it?

4.

What is the difference between charging by contact and charging by induction in terms of electron transfer?

5.

What is grounding?

Electrical Discharge

Once an object is charged, the charges are trapped on it until they are given a path to escape. When electric charges are transferred very quickly, the process is called an electrical discharge . Sparks are an example of electrical discharge (Figure 10.20).

Have you walked across a carpet and reached for a doorknob only to be shocked when you created a spark (Figure 10.21)?

When you shuffle your feet in slippers or socks on a carpet, electrons are transferred through friction and you build up a static charge. When your hand reaches toward the neutral doorknob, the excess electrons transfer due to induction.

Figure 10.20

When a spark occurs, the air becomes a passage for the electrons to travel. Collisions between moving electrons and air particles release light and can also make a crackling sound.

Transfer of charge from girl to door

9G10.42

Transfer of charge from carpet to girl

Figure 10.21 When electrons jump between your hand and a doorknob, you can receive a surprising shock.


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Lightning

Lightning is an example of a very large electrical discharge caused by induction. In a thunderstorm, a charged area, usually negative, builds at the base of the cloud (Figure 10.22 (a)). The negative charge at the base of the cloud creates a temporary positive area on the ground through the induction process (Figure 10.22 (b)).

When enough charge has built up, a path of charged particles forms (Figure 10.22 (c)). The cloud then discharges its excess electrons along the temporary path to the ground, creating a huge spark — lightning (Figure 10.22 (d)). This discharge creates a rapid expansion of the air around it, causing the sound of thunder.

electrons electrons

(a) (b) (c)

Figure 10.22

Lightning is an atmospheric discharge of electricity.

(d)

It is interesting to note that air is normally an insulator. If it were not, lightning would occur every time that clouds formed.

For lighting to occur, charges in the clouds must build up to the point where the air cannot keep the charges separated from the ground. At this point, the air stops being an insulator and becomes a fair conductor, resulting in a lightning strike.

Earth is a donator or receiver of charge and is so large that overall it is not affected by the electron transfer of huge lightning strikes. As a result, the ground is always considered neutral.


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Electrostatic Generators

Scientists use several devices in the laboratory to study how static charges create lightning and other phenomena, such as the static that affects clothes coming out of the dryer.

Early electrostatic generators were called “friction machines” because they used direct contact between different surfaces to create charged areas. A glass sphere or cylinder was rubbed mechanically by a pad to charge it up.

More recent machines, such as the Van de Graaff generator, create charge through friction between the roller and belt and then transfer the charge to a large metal sphere, as shown in

Figure 10.23. charge collector metal sphere

Take It Further

Sometimes, lightning strikes start from the ground and go to a cloud. There are also cloud-tocloud lightning strikes. Find out more about different types of lightning. Create a visual display of your findings. Use ScienceSource as a starting point.

Teflon™ roller rubber belt insulating support nylon roller motor-driven pulley

Figure 10.23 (b) The static charge on a Van de Graaff generator has a hair-raising effect on these students.

comb

Figure 10.23 (a) This Van de Graaff generator is set up so its dome is negatively charged. A Van de Graaff generator can also be charged positively by using different roller materials.

A Wimshurst machine creates charges on two slowly rotating disks with metal strips placed around the disks

(Figure 10.24). The charge is built up using induction between the front and back plates as the disks turn in opposite directions. The excess charge is collected by metal combs with points near the turning disks.

Figure 10.24

The Wimshurst machine uses induction to build up charge and create sparks.


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D5 Quick Lab

Charge Sorter

Materials that tend to lose electrons are higher on a triboelectric series. Materials that tend to gain electrons are lower on a triboelectric series.

Purpose

To sort materials based on their ability to hold on to static charge


• materials such as fur, silk, aluminum, paper towel, leather, wood, amber, hard rubber, Styrofoam®, plastic wrap, vinyl (PVC) and Teflon®

• metal-leaf electroscope

• known charged object, such as an ebonite rod rubbed on fur to create a negative charge

CAUTION: Some people are allergic to fur.

Procedure

3.

4.

1.

2.

1.

Make a table like the one below to list your materials, predictions, and results. Give your chart a title. Record your predictions.

Materials

Prediction of Charge

Actual

Charge

A B A B A B fur fur silk silk silk aluminum aluminum paper

2.

Record your predictions for what charge each material in each pair will have when the materials are rubbed together.

3.

Rub together the first pair of materials, A and B.

Then, touch material A to the knob of the electroscope to charge the electroscope.

4.

Use a charged ebonite rod to test the charge on the electroscope by bringing it near the knob.

Do not touch the rod to the electroscope

(Figure 10.25). Observe the motion of the leaves.

5.

Record the charge of material A.

6.

Ground the electroscope by touching it with your hand. Then, charge the electroscope using material B.

7.

Use a charged ebonite rod to test the charge on the electroscope by bringing it near the knob.

Do not touch the rod to the electroscope.

Observe the motion of the leaves.

8.

Record the charge of material B.

9.

Repeat steps 3–8 for each pair of materials.

Questions

10.

Which materials were good electron receivers and would appear lower on a triboelectric series?

11.

Which materials were good electron donors and would appear higher on a triboelectric series?

12. Create a triboelectric series by listing the materials you used in order, according to their electron affinity.

Figure 10.25

To test the charge on the electroscope, bring the charged ebonite rod near it. Do not touch it.


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Charging by Contact

Question

What charge does the electroscope gain compared to the charging rod?


• ebonite rod

• fur


Trial A

• glass rod

• silk


Procedure

1.

Make a table like the following to record your predictions and observations. Give your table a title. Record your predictions.

Trial

Trial A ebonite rod touching ebonite rod near glass rod near

Trial B glass rod touching glass rod near ebonite rod near

Motion of Leaves

Predictions Observations

2.

Charge the ebonite rod by rubbing it with the fur.

3.

Brush the ebonite rod against the top of the electroscope. Record your observations of the electroscope leaves using a labelled diagram.



Making predictions

Observing, and recording observations

4.

Rub the ebonite rod with the fur again. Bring it near, but not touching, the top of the electroscope. Record your observations using a labelled diagram.

5.

Charge the glass rod by rubbing it with silk. Bring the glass rod near, but not touching, the top of the electroscope. Record your observations using a labelled diagram.

6.

Touch the top of the electroscope with your hand.

Trial B

7.

Repeat steps 2–4 using a glass rod charged with silk. Use a charged ebonite rod in steps 5. Repeat step 6.

8.

Return all materials to the areas designated by your teacher.


9.

(a) Explain why the leaves moved when the ebonite rod touched the electroscope in step 3.

(b) What charge was left on the electroscope?

10.

(a) Explain why the leaves moved when the glass rod touched the electroscope in step 5.

(b) What charge was left on the electroscope?

11.

How do your predictions compare with your observations?

12.

In terms of charge movement, explain in words and diagrams the effect of:

(a) an identically charged rod near the electroscope

(b) an oppositely charged rod near the electroscope

Skill Practice

13.

Explain how you would find the charge of an unknown material.


14.

Write a summary statement about the charge the electroscope gains and the charge of the influencing rod.


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Charging by Induction

Question

What charge does the electroscope get compared to the charging rod?


• ebonite rod

• glass rod

• silk


Procedure

• fur


1.

Make a table like the following. Give your table a title. Record your predictions.

Trial

Trial A ebonite rod away ebonite rod near glass rod near

Trial B glass rod away glass rod near ebonite rod near

Motion of Leaves

Predictions Observations

Trial A

2.

Charge the ebonite rod by rubbing it against the fur.

3.

Bring the ebonite rod near the electroscope. Be careful not to touch the rod to the electroscope.

While you hold the rod there, touch the top of the electroscope with your hand.



Gathering, organizing, and recording relevant data from inquiries

Interpreting data/information to identify patterns or relationships

4.

Remove your hand from the electroscope, and then move the ebonite rod away. Observe what happens to the leaves of the electroscope.

Record your observations.

5.

Bring a charged ebonite rod near the electroscope.

Record what happens to the electroscope leaves.

6.

Bring a charged glass rod near the electroscope.

Record what happens to the electroscope leaves.

Trial B

7.

Repeat steps 2–5 except start by charging a glass rod against silk in step 2. Use a charged ebonite rod for step 6.


8.

(a) Compared to the original rod that was brought near the electroscope, what charge did the electroscope end up with?

(b) How do you know?

9.

Explain what happens to the electrons in the electroscope when your hand touches the electroscope.

10.

(a) Why did you have to remove your hand first before you moved the rod away?

(b) What would have happened if you had moved the rod away and then your hand?

Skill Practice

11.

How else could you ground the electroscope?


12.

Summarize the method of charging by induction by using diagrams labelled with the motions of charges.


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10.2



1.

How are lightning and a spark similar?

2.

(a) How do objects become negatively charged using the contact method?

(b) How do objects become positively charged using the contact method?

3.

Explain how a substance becomes temporarily charged by induction when a charged object is brought near.

4.

Explain how to charge an object permanently using induction.

5.

Using a sequence of labelled diagrams, explain how a positive balloon will stick to a neutral wall. Under each diagram, describe the motion of the charges.


6.

(a) How does the process of grounding occur when you receive a spark from touching a metal shopping cart?

(b) How does the process of grounding occur during a lightning strike?

7.

What would change about the way an electroscope worked if its metal knob were replaced with a plastic knob? metal knob

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Question 8

9.

A person walks across a carpet, touches a metal doorknob, and receives a shock. If the same person were carrying a metal rod, she would not experience a shock when touching the doorknob. Why?

10.

Suppose a five-year-old child asks you to explain why there is lightning. Write a simple explanation that you could share with the child. You may wish to include a diagram.

Reflection

11.

What are two things about static electricity that you know now but you did not know before you started this chapter?


Question 7

Quit

8.

(a) Why do the leaves of the charged electroscope shown below move farther apart if a rod with the same charge is brought near?

(b) Why would the leaves move closer together if the rod had the opposite charge to the electroscope?

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Electrostatics in Our Lives


• Lightning rods are used to prevent damage to buildings.

• Grounding static charges can help prevent sparks near flammable fuels.

• Paint sprayers work better if the object and the paint have different charges.

• Photocopiers use electrostatic principles in their operation.

• Grounding wires prevent damage to electrical equipment.

• Electrostatic precipitators work by creating charged waste particles and using electrostatic attraction to remove the particles.

Figure 10.26 Lightning can strike tall buildings repeatedly during a storm. The CN Tower

(extreme right of photograph) is struck by lightning more than 70 times a year.

416

Lightning Storm Awareness

On a hot and humid summer night, lightning strikes a building in

Toronto (Figure 10.26). Along with the lightning, there would have been loud claps of thunder. You may have noticed that as a storm moves closer, the time between lightning and thunder decreases. This occurs because lightning travels very fast, at the speed of light. Thunder travels much more slowly, at the speed of sound. If you see lightning and hear thunder at the same time, the storm is right above you.

Summer storms are common in Ontario and across Canada, but many people do not know what to do in these extreme weather conditions. Lightning storm safety begins by watching for towering cloud formations that signal developing storms.

Lightning can strike up to 15 km from where it is raining. As a guideline, if you can hear thunder, you are in striking distance and should look for shelter.

Safe shelter includes a large building because it will be properly grounded if there is a strike. Cars, school buses, and other vehicles are also safe places, provided that the windows are rolled up and you do not touch metal parts of the vehicle.


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If no safe shelters are available, you should avoid the highest point of land because lightning tends to hit these areas. Remain in a safe place for about 30 minutes after the last thunderclap.

A dangerous place to take shelter during a lightning storm is under a tree, as the tree may be the highest point in the area. This makes it more likely to be struck by lightning. Also stay away from objects that conduct electricity, such as bicycles, lawnmowers, and golf clubs. Summertime presents a higher risk of being struck by lightning both because there are more lightning storms and because more people are outdoors participating in activities such as baseball, swimming, fishing, and boating.

Lightning strikes cause about six deaths per year in Canada and result in injuries to about 60 people. All of these could be prevented if everyone follows the few careful steps just described as the storm approaches.

D8

STSE Quick Lab

Lightning: Facts and Fiction

Purpose

To separate lightning facts from lightning fiction

Procedure

1.

As a class, read the following true account of one man’s close encounter with a lightning strike.

Then, discuss the questions that follow.

A man was digging post holes in a large open field. One of the tools he was using was a 2 m steel bar, which he used to pry rocks from the ground. He was working in stormy weather and wanted to finish a bit more work before taking cover.

Suddenly, he could feel the hairs on his arms and legs begin to stand up. He threw the steel bar as hard as he could and dove for the ground. Then, he heard a deafening blast of sound. The lightning strike missed him, and he ran for cover.

Later, after the storm, he went back to the site. The ground around the bar was blackened, and one end of the bar appeared to have melted.

Questions

2.

What was his hair standing up an indication of?

3.

(a) Holding a steel bar when the lightning struck would almost certainly be lethal. Why?

(b) Would it make any difference if the steel bar being held had one end in the ground when lightning struck? Explain why or why not.

4.

Describe the path the lightning may have taken to result in blackened ground and a melted end of the steel bar.

5.

What could the man have done differently in order to be safer during the storm?

6.

Describe how to keep safe if you find yourself outside during a thunderstorm.

7.

If you find yourself out in the open during a thunderstorm, you should crouch, keep your feet close together, and stay on your toes.

(a) Why should you crouch on your toes?

(b) Why should you keep your feet close together?


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Figure 10.27

A tree burned by lightning

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Lightning Rods

When lightning strikes a tree, the sap inside the tree conducts the electricity down to the ground. In the process, the tree heats up and expands very rapidly, resulting in an explosion and fire

(Figure 10.27).

If the tree had been wet on the outside and dry on the inside, the electricity might have followed a different path to the ground and left the tree unharmed. Or if there had been a conductor, such as a metal rod, that was slightly taller than the tree and that was connected to the ground, the lightning strike could have followed the conductor safely to the ground and left the tree unharmed.

A lightning rod is a metal pole with a wire attached to it that runs down to the ground. The main purpose of a lightning rod is to provide a point removed from the main structure of a building where a stream of electrically charged particles is more likely to form. The stream of electrically charged particles is highly conductive, so if lightning strikes in the area around the building, it is much more likely to strike the lightning rod (Figure 10.28).

This decreases the total amount of electric charge in the building, which makes it less likely to be struck by lightning. If lightning hits the lightning rod, the flow of electrically charged particles is directed harmlessly down to the ground so the building is not damaged, as shown in Figure 10.29.

Figure 10.28

The point on top of this weather vane is a lightning rod.

lightning rod insulated grounding wire

Figure 10.29

The lightning rod redirects the electrical strike away from the barn and harmlessly into the ground.

418 UNIT D The Characteristics of Electricity ground rod

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Grounding Static Charges on Vehicles

Friction occurs when two surfaces rub against each other. The surfaces may be solids, such as silk or glass, or they may be fluids, such as air or water. Automobiles and airplanes build up charge through friction between the vehicle’s outer surface and the air. A simple way to prevent static build-up on a car is to use a ground strap (Figure 10.30). However, dragging a strap along the ground would not be a practical solution for airplanes.

Airplanes have needle-like projections located in various places on the wings and plane body, as shown in Figure 10.31.

The force of repulsion between charges becomes so strong around a point that charges will disperse into the air from the point.

During Reading

Determining the Key Idea

Good readers synthesize details from a text to determine the key idea. To do this, you make connections among the important ideas in the text, asking yourself the question “How does this information connect to that information?” As you read pages

418 to 420, ask yourself how the information on one page connects to the information on another page. What is the single key idea presented on these pages?

Figure 10.30

Some drivers use a grounding strap to prevent static charges from building up on their cars.

Figure 10.31 These needle-like rods on the wing of an airplane disperse static charges into the air.

Static Charges and Flammable Materials

Static charge build-up is particularly dangerous when using flammable materials (Figure 10.32). When airplanes are fuelled, the very explosive fuel moving through the nozzle creates a build-up of static charges.

If the nozzle comes too close to the plane’s body, a spark could ignite the fuel. In order to prevent this from occurring, the nozzle and fuel truck are connected to the ground. Sparks are also dangerous near the gas pumps at service stations. It is a good idea to ground yourself at a service station by touching a metal door handle before you slide across the seat to exit a vehicle.

Figure 10.32

The nozzle and fuel truck must be grounded before refuelling an airplane begins.


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Figure 10.33

You can reduce the build-up of static charges by drying only the same types of materials at one time.

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Reducing Static Charges in the Home

You can use your knowledge of static charges to help you understand how to reduce charges. For example, static charges are built up when different types of insulators, such as nylon and polyester, rub together. This is why clothes made of different materials often stick together when they come out of a clothes dryer (Figure 10.33).

More charges build up in dry air, such as during winter, because dry air acts as an insulator. Moist air is a fair conductor, so fewer charges build up on humid days. If you remove clothes from the dryer before they are completely dry, there will be fewer charges on them.

Sometimes, people add an antistatic dryer sheet to a clothes dryer. The dryer sheet adds a thin layer of waxy chemicals to the surface of clothes so there is less friction between the surfaces and therefore fewer unlike charges to attract each other.

Sparks caused by static charges can damage sensitive electronic equipment. People who work with this type of equipment take special care to reduce the risk of sparks. For example, carpets can cause static build-up.

Ways to reduce the risk of static sparks from carpets include:

• using an antistatic mat for your feet

• increasing the moisture in the air by using a humidifier

• spraying the carpet with antistatic spray

• wearing an antistatic wrist strap

(Figure 10.34)

• removing the carpet from the computer room

Figure 10.34

This computer technician wears an antistatic wrist strap to reduce the build-up of charges.


1.

What is the function of a lightning rod?

2.

How is charge build-up reduced on airplanes?

3.

Why is a ground strap a necessary safety feature when transferring fuel?

4.

What are three different methods for reducing charge build-up in clothes dryers?

5.

What are four different methods for reducing charge build-up in a computer room with a carpet?


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Making Use of Static Charges

Static electricity can be a nuisance when it causes flyaway hair or sparks in your living room. It can be extremely dangerous when it occurs near flammable materials or electronic equipment.

However, static electricity can also be useful. Our ability to control and direct static electricity has allowed us to design technological devices that make use of it to improve our lives.

Spray Painting

If you have ever tried spray painting, you may have found it to be a challenging job. The paint comes out in a mist, and you lose a lot of paint because it doesn’t all land on the object you’re trying to paint. The paint comes out of the spray gun at a high speed, so the paint particles bounce off the object being painted, wasting paint.

Electrostatics can help! Figure 10.35 shows a worker making use of electrostatics to paint a car. The paint coming out of the nozzle gains a negative charge through friction. The surface of the car has been given a positive charge. Unlike charges attract, so the paint is attracted to the surface of the car. There is less waste due to bounce and overspray, and the finish is smooth and uniform.

Figure 10.35

Industrial sprayers such as those used to paint cars and boats take advantage of the laws of static charges.


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Take It Further

Laser printers make use of electrostatics in the printing process. Find out how a laser printer works. Start your research at ScienceSource .



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Photocopying

The word “photocopy” means to copy using light. Figure 10.36

shows the typical steps involved in photocopying, including the role of electrostatics.

Step 1

A positive charge is created on the drum. The drum is an insulator, but it becomes a conductor when exposed to light. For this reason, it is called a photoconductor.

Step 3

Plastic particles and toner (ink) are sprayed onto the drum. As the particles come out of the sprayer, they get charged negatively. The negatively charged toner sticks to the positively charged areas on the drum, creating a copy of the original paper.

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Step 2

The image on the paper to be photocopied is projected onto the drum. Where the light hits the drum, the area becomes conductive, loses its charge, and becomes neutral. The dark areas remain positively charged.

Step 4

A sheet of paper is pressed against the drum and heated. Heat and pressure cause the toner to fuse to the paper. In some photocopiers, the paper is also charged to help the toner stick to it.

page to be copied light source lens

⫹⫹ ⫹

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Step 5

The paper is still charged and may be warm when it comes out of the photocopier.

Figure 10.36

A model of a photocopying process


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Environmental Applications

An electrostatic precipitator makes use of the laws of static charges to clean air (Figure 10.37). The gas discharged from a factory can contain tiny particles of pollutants, called particulate matter. One way to clean the gas before it is released is to send it through pipes that charge the particulate matter negatively. The gas then moves through an area that has positively charged plates.

The positive plates attract the negative particles and remove them from the gas. These collector plates are cleaned periodically to keep the system running efficiently. Industrial plants that produce cement, steel, lumber, and petrochemicals use similar techniques to remove dust from the air.

We also use electrostatics in processes that purify and sort materials, such as ore separation in mining, plastics and paper recycling, and the settlement of fine particles suspended in water.


D11 Quick Lab on page 425 clean gas out

Electrostatic

Precipitator polluted gas in conductors

(metal plates) grounding wire solid waste collection

Figure 10.37

An electrostatic precipitator uses static electricity to remove particulates from gases in buildings or industrial sites.


Advertisements for Static Control Products

If you have a problem with flyaway hair, clothes sticking together in the dryer, or dust that will not stick to a mop, chances are there is a consumer product that has been designed to help you.

Discuss the following questions with your group and record your answers.

1.

Give examples of products that help consumers with static control.

2.

Are these products essential for everyday living?

Why or why not?

3.

(a) What do advertisers say about static in their messages to try to convince you to buy their products? Is this information accurate?

(b) Do you think they are successful in convincing people? Explain your answer.


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D10 Quick Lab

Make Your Own Photocopier

Imagine painting your name on a piece of paper using a paint that attracts electrons. Suppose you then rubbed the paper with fur, causing your painted name to gain a negative charge. You could sprinkle cocoa or flour on the paper and the neutral cocoa or flour would be attracted to the charged paint. The cocoa or flour would stick to your name, spelling it out in black or white. This is basically how a photocopier works. In this activity, you will investigate a variation of this technique.

Purpose

To investigate the principles of photocopying

3.

Add cocoa or flour to the dish. Jiggle the dish in order to spread the cocoa or flour evenly.

4.

Using a minimum of tape, attach the edge of the circle to the outside of the lid.

5.

Using the wool cloth, gently rub the lid area showing through the paper for about a minute, as shown in Figure 10.38.


• paper and scissors

• plastic petri dish and lid


• cocoa or flour

• wool cloth

Figure 10.38

Rub the lid gently.

CAUTION: Never eat anything in science class.

Procedure

1.

Cut a paper circle the size of the petri dish.

2.

Turn the paper into a stencil by cutting out a simple symbol such as a diamond or your initial.

6.

Carefully remove the stencil. Put the lid on the dish.

7.

Turn the dish upside down while holding the lid.

Then, turn it right side up.

8.

Remove the lid. Record your observations.

Questions

9.

What did you observe in step 8?

10.

How would you explain your observations?


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D11 Quick Lab

Make Your Own Precipitator

An electrostatic precipitator uses static charges to separate particles in order to purify and sort materials.

Purpose

To study how an electrostatic precipitator works


• paper towels

• ground pepper

• flour

• salt

• lint

• 3 balloons

Figure 10.39

Pull the paper towel across the table slowly.

CAUTION: Never eat anything in science class.

Procedure

1.

Lay a long piece of paper towel on a table.

Sprinkle pepper, flour, salt, and bits of lint on the paper towel.

2.

Inflate and tie off three balloons. Charge the balloons by rubbing them against your hair or a sweater. Hold the balloons above the table but not directly above or touching the paper towel.

3.

Have a partner pull the paper towel across the table slowly under the balloons (Figure 10.39).

Observe which materials are taken up and how much of the material is left.

4.

Clean the balloons and recharge them. Repeat step 3 with the remaining particles on the towel.

5.

Clean up your work area. Wash your hands thoroughly.

Questions

6.

(a) Which particles were the easiest to pick up?

(b) Which particles were difficult to pick up?

Explain why.

7.

What happened to the ability of the balloons to pick up particles as time went on?

8.

Why do you think this method is used to remove particulate matter from the air?

9.

What factors would affect the efficiency of a precipitator?


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Home


1.

Why is it not a good idea to take shelter under a tree in a thunderstorm?

2.

(a) What are the three parts of a lightning protection system for a building?

(b) What is the function of each part?

3.

What causes the static build-up on moving vehicles such as cars and airplanes?

4.

Large trucks that carry flammable liquids often have a metal wire or chain that drags on the ground. Why?

5.

Sometimes, finished photocopied paper will stick to you. Explain why.

6.

Name four applications that use electrostatic principles.


7.

Why does Earth not become charged when many people in the world ground objects?

8.

How can neutral pollutant particles be made attractive to the charged plate in an electrostatic precipitator?

9.

The technician in this photo is using a tool that has insulated handles. Why is this important for working on electronic equipment?

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10.

When spray paint is applied to a car, the paint has a negative charge and the surface of the car has a positive charge. Some processes use a negatively charged paint and a grounded object. Explain why this also works.

11.

Flowing fluids, such as water, oil, and air, produce static charge. Why is it not as important to create static charge safety rules for handling flowing water as for handling air or oil?

12.

Suppose you have a static charge problem at home. Your clothes stick to your body, there are socks stuck to your sweater from the dryer, and you always get a shock from touching a doorknob after walking across your carpet. Suggest ways you can reduce or eliminate these and similar problems.

13.

Explain the importance of protecting computer equipment from static discharge.

14.

Explain how eliminating static electricity would hinder the performance of a spray painting device.

15.

Suppose a building had a lightning rod that was not connected to a ground rod by a conducting wire. Would this set up still provide protection from lightning strikes?

Explain.

Reflection

16.

Which device that makes use of static electricity has the greatest effect on your life? Why?


Question 9


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S C I E N C E

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This device is sometimes called a

“pacemaker for the brain.” A pacemaker is an implanted device that supplies electric signals to the heart to help it beat regularly.

A brain pacemaker causes deep brain stimulation. It stimulates the brain by sending electric impulses to target areas deep within the brain. These electric impulses interfere with naturally occurring electric impulses in the brain that cause uncontrolled shaking, called tremors, in a patient. Tremors are a symptom of several conditions, including Parkinson’s disease.

Tremors can prevent people from walking, feeding themselves, or even just being able to sit still.

Before receiving the deep brain-stimulating device, this patient was unable to control his arms and was unable to speak clearly. With his new implants sending electric signals to his brain, he is able to use his steady hand to enjoy a hot cup of coffee without worrying about spilling it and burning himself.

This X-ray shows how deeply the two electrodes are placed inside the brain. The electric signals are generated by a small device implanted in the patient’s chest, near the shoulder. The electric circuits are programmed using a computer that contacts the device using radio signals. This means the electric impulses can be adjusted with the device implanted in the patient’s body. Using special magnets, patients or their doctor can even turn the deep brain stimulator on or off.

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10 CHAPTER REVIEW

ACHIEVEMENT CHART CATEGORIES k

Knowledge and understanding t

Thinking and investigaion c

Communication a

Application


1.

(a) What are the possible interactions between two charged objects? k

(b) How do a charged object and a neutral object interact? k

2.

Explain the role of friction in creating a charged object. k

3.

(a) Two neutral objects, A and B, were rubbed together, resulting in object A being charged positively. What is now the charge on B? k

(b) How do you know? k

(c) Which object, A or B, is likely higher on the triboelectric series? k

(d) How do you know? k

4.

For the following three electroscopes, explain which way the leaves will move when a charged rod is brought near.

Explain your reasoning. t

5.

(a) Describe how to leave an object positively charged using the induction method. k

(b) Describe how to leave an object negatively charged using the induction method. k

6.

How would you ground an electroscope?

7.

(a) Define electrical discharge. k

(b) What is a real-life example of an electrical discharge? k

8.

Describe a device that uses static electric charges. Include a labelled diagram as part of your answer. c

9.

Describe a device that protects other devices by controlling static electric charges. Include a labelled diagram as part of your answer. c


10.

Explain why a positively charged balloon will stick to a wall just as easily as a negatively charged balloon.

t

11.

Would the humidity (moisture content) of the air make a difference in the photocopying process? Explain. t

+ +

+

–

–

–

–

–

–

+

–

+

– +

+ +

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(a) (b)


+

(c)

–

–

–

–

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12.

Suppose you had a plastic lightning rod that was the same size and design as a metal lightning rod. Would the plastic lightning rod work better than, the same as, or not as well as a metal lightning rod? Explain your answer. t

13.

Would a negatively charged balloon stick to a metal wall as easily as to a wooden wall?

Explain why it would or would not. t

14.

You have an unknown material that becomes charged when you rub it with silk.

You also have a negative ebonite rod and a positive glass rod. How can you determine the charge of the unknown object? t

15.

If lightning hits a car, the effect is minimal.

Explain why. a

16.

Two identical objects are both charged positively, but one object has about twice as much positive charge as the other object.

What would happen to the charges when the two objects are brought together?

Explain your answer. t

17.

(a) How would using a humidifier in a home affect static charge build-up? a

(b) Would you need to use a humidifier more in the summer or the winter?

Explain. a

18.

Explain two different actions that could cause static charges to build up on a computer. a

19.

If you wrap plastic wrap on a glass bowl, the plastic wrap will cling to the bowl. Use your understanding of static charge to explain why. a

20.

You run a brush through your hair and wonder if it has become statically charged.

Design a test that allows you to determine if the brush has a charge. t

21.

What materials could be woven into a polyester carpet to prevent a static charge from building up on a person walking across the carpet? Explain the reasons for your choice. a

Reflection

22.

What information from this chapter surprised you or was not what you expected? Explain why. c

23.

(a) How would you rate your participation in the labs you did in this chapter? c

(b) How could you improve your participation? c

After Reading

Reflect and Evaluate

Revisit the key learning goals that you set in the

Before Reading activity at the start of this chapter.

How did the During Reading strategies help you to accomplish your goals? Write a paragraph that summarizes how the reading strategies assisted your learning. Compare your paragraph with a partner’s. Add any new insights you gained from reading your partner’s reflection.

Unit Task Link

Storing large amounts of electricity is very difficult.

This means that electricity is usually generated as it is being used. Generating facilities increase and decrease the amount of electricity they produce depending on how much electricity the community is using at any given time. Explain how an electrical grid connecting many different electrical generating sources and several communities provides a dependable source of electricity. Brainstorm a list of different ways of generating electricity. Sort them from most important to least important. Share your ideas with your class.


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11



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Millions of light bulbs light up the Toronto skyline.

Each light bulb is lit because of the movement of electrons through the wires that connect the bulbs.

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• design, draw, and construct series circuits and parallel circuits

• analyze the effects of adding an identical load in series and in parallel

• investigate the relationships between potential difference, current, and resistance

• solve simple problems using the formula V = IR



• describe the relationship between potential difference, current, and resistance

• explain what different meters measure and how they measure electrical quantities

• identify and explain the parts of a simple circuit

• explain the characteristics of electric current, potential difference, and resistance and how they differ in series and parallel circuits

• explain how different factors change the resistance of an electric circuit


Every electrical appliance or device that you use includes one or more electric circuits. Understanding how electrical energy is produced, transferred, and converted into other forms of energy will help you handle electrical devices safely.

Before Reading

Learning Vocabulary in Context

This chapter contains many new terms related to electricity. Skim and scan section 11.1 for the ways that vocabulary is supported. Where can you find definitions?

How are unfamiliar terms highlighted in the text? What special features explain terms or words? Begin a personal list of unfamiliar terms, adding definitions as you find them in the chapter.

Key Terms

• ammeter • amperes • battery • electric current • fuse

• load • ohms • potential difference • resistance

• switch • volt • voltmeter

Current electricity is the continuous flow of electrons in a closed circuit.

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Current, Potential Difference, and Resistance


• An electrochemical cell generates a potential difference by creating an imbalance of charges between its terminals.

• Potential difference is the difference in electric charge between two points that will cause current to flow in a closed circuit.

• Current is the rate of movement of electrons through a conductor.

• An electric circuit is a path along which electrons flow.

• Resistance is the ability of a material to resist the flow of electrons.

• Resistance in a wire depends on wire length, material, temperature, and crosssectional area.

Figure 11.1

The elephantnose fish has tiny electric sensors in its nose that help it find food.

Figure 11.2

The electric eel uses electricity to defend itself and to stun its prey.

Electric Fish, Eels, and Rays

You probably know that when it comes to electrical safety, it is very important to keep electrical devices away from water. For some animals, this safety concern about electricity is not a problem. In fact, they survive because they can use electricity in the water.

The elephantnose fish from central Africa has an extended nose that contains about 500 electric sensors (Figure 11.1) These sensors are used to help this tiny fish find food. The elephantnose fish hides for protection during the day and comes out to feed at night. The electric sensors help it find smaller living things crawling along the bottom of the river or swimming in the water.

Research has shown that these electric sensors are so sensitive that they can detect chemical pollutants. Further research will determine if this type of sensor can be used to monitor the levels of pollutants in rivers.


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The electric eel in Figure 11.2 lives in the murky waterways of the Amazon and Orinoco river basins of South America. It’s really a fish and not an eel, but it really is electric — and dangerous. The eel’s electricity comes from a special organ in its long tail that contains thousands of muscle cells that work like tiny batteries. Each cell can produce only a small amount of electricity, but by working together all the cells can produce controlled bursts of electricity equal to five times the energy of a standard wall socket. These electrical bursts are used to stun prey when the electric eel is hunting for food. Some electric eels also generate an electric signal to attract a mate.

The Pacific electric ray, found along the west coast of North

America, has an electric organ located in its head (Figure 11.3).

This organ can generate enough electricity to knock down a human. Other types of electric rays use these electric shocks for defense when they are attacked. Rays belong to a category of animals called Torpedo. The name for this category comes from the Latin word torpidus, which means numbness. This term describes what happens to a person who steps on an electric ray.

Figure 11.3

A Pacific electric ray can send out a powerful electric shock.

D12 Quick Lab

Light the Lights

In this activity, you will use a combination of wires, light bulbs, and an electrochemical cell to investigate how a steady, controlled flow of electrons can cause the bulbs to light up.

Purpose

To discover how to make flashlight bulbs light up using a standard battery


• 1 D dry cell

• 5 insulated copper wires with both ends bare

• two 2.0 V-flashlight bulbs

Procedure

1.

Use wire and the dry cell to make one bulb light up. Record your arrangement.

2.

Use wire and the dry cell to make two bulbs light up. Record your arrangement.

3.

If time allows, try other arrangements for step 1 and step 2.

Questions

4.

Explain how to use wire and a dry cell to make one bulb light up. Include a labelled sketch in your answer.

5.

Explain how to use wire and a dry cell to make two bulbs light up. Include a labelled sketch in your answer.

CAUTION: Disconnect the wires if they get hot. Do not use dry cells if they show any sign of corrosion.


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During Reading

Illustrations

Support Understanding of

Vocabulary

As you read the text, be aware of how the photos, diagrams, or other illustrations support your understanding of unfamiliar vocabulary. What term or concept is illustrated by the photo or diagram? How does the illustration make the concept easier to understand? If you get stuck on unfamiliar terminology, check the illustrations as one way to improve your understanding.

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Current Electricity

The electricity of the electric eel and the electric ray is similar to the static charges you have felt from a sweater or the huge static charges of lightning. Unfortunately, static charges are not useful for operating electrical devices. They build up and discharge, but they do not flow continuously.

To operate electrical devices, you need a steady flow of electrons. Unlike static electricity, a flow of electrons moves continuously as long as two conditions are met. First, the flow of electrons requires an energy source. Second, the electrons will not flow unless they have a complete path to flow through. This path


The word “circuit” comes from a

Latin word meaning to go around.

The word “circuit” can also be used to describe a complete journey of people or objects, such as the circuit of Earth around the Sun.

Electric Circuits

A circuit includes an energy source, a conductor, and a load. An another form of energy. For example, in Figure 11.4, the light bulb is the load. It converts electrical energy to light and heat. device that turns the circuit on or off by closing or opening the circuit. When the switch is closed, the circuit is complete and electrons can flow. An open switch means there is a break in the path, so the electrons cannot flow through the circuit. The circuit is turned off when the switch is open.

electrical load energy source

+ conducting wires

– switch

Figure 11.4

An electric circuit


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Electrochemical Cells

cceellll is a package of chemicals that converts chemical energy into electrical energy that is stored in charged particles. A simple electrochemical cell includes an electrolyte and two electrodes.

• An electrolyte is a liquid or paste that conducts electricity because it contains chemicals that form ions. An ion is an atom or a group of atoms that has become electrically charged by losing or gaining electrons. Citric acid is an example of an electrolyte.

• Electrodes are metal strips that react with the electrolyte.

Two different electrodes, such as zinc and copper, are used in a battery.

As a result of the reaction between the electrolyte and electrodes, electrons collect on one of the electrodes, making it negatively charged. The other electrode has lost electrons, so it is positively charged (Figure 11.5).

copper electrode (+) zinc electrode (–)

F

Figure 11.5

The citric acid in the grapefruit is the electrolyte. Electrons collect on the zinc electrode, leaving positive charges on the copper electrode. The meter measures the flow of electrons.

A

B

C

D

Wet Cells and Dry Cells

An electrochemical cell that has a liquid electrolyte is called a wet cell . Wet cells are often used as an energy source for cars and other motorized vehicles. An electrochemical cell that uses a paste instead of a liquid electrolyte is called a dry cell (Figure 11.6).

You use dry cells in flashlights, hand-held video game devices, cameras, and watches. Each electrode in a dry cell or battery can also be called a terminal. Terminals are the end points in a cell or battery where we make a connection.

E

A – zinc powder and electrolyte, where electrons are released

B – electron collecting rod

C – separating fabric

D – manganese dioxide and carbon, where electrons are absorbed

E – negative terminal, where electrons leave

F – positive terminal, where electrons return

Figure 11.6

An alkaline dry cell


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Recycling and Recharging Dry Cells

Eventually, the chemicals in a dry cell are used up and can no longer separate charges. When you are finished using a dry cell, you should recycle it rather than discard it (Figure 11.7). Dry cells can contain toxic materials, such as the heavy metals nickel, cadmium, and lead. Household dry cells and batteries are responsible for over

50 percent of all the heavy metals found in landfills.

Figure 11.7

During recycling, the chemicals in a dry cell are separated and can be reused.

Some dry cells are rechargeable cells.

Chemical reactions in a rechargeable cell can be reversed by using an external energy source to run electricity back through the cell. The reversed flow of electrons restores the reactants that are used up when the cell produces electricity. Since rechargeable dry cells can be reused many times, they have less impact on the environment than non-rechargeable dry cells.

Fuel Cells

A fuel cell is an electrochemical cell that generates electricity directly from a chemical reaction with a fuel, such as hydrogen

(Figure 11.8). The cell is not used up like an ordinary cell would be because as the electricity is produced, more fuel is added.

Much of the energy produced by fuel cells is wasted as heat, but their design continues to be refined. Fuel cells are used in electric vehicles and may one day be used in smaller devices such as laptop computers.

Figure 11.8

A fuel cell converts chemical energy into electrical energy. This fuel cell is slightly smaller than this textbook.


1.

How is current electricity different from static electricity?

2.

What is an electric circuit?

3.

List three components of an electric circuit.

4.

What is the difference between an electrolyte and an electrode?

5.

Why should dry cells be recycled rather than thrown in the trash?


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Potential Difference

Each electron has electric potential energy. Potential energy is the energy stored in an object. Picture an apple hanging from a low branch on an apple tree (Figure 11.9). The apple has potential energy because of its position above the ground. If the apple falls down, it will convert its stored energy, or potential energy, into motion. Suppose an apple were on a higher branch. It would have even more potential energy to convert.


The electrochemical cell was first presented to the Royal Society of

London in 1800 by the Italian physicist Alessandro Volta. The words

“voltage and “volt” are named in his honour.

Figure 11.9

The greater the height of an apple above the ground, the greater its potential energy.

A battery has chemical potential energy in the electrolyte in its electrochemical cells. The chemicals in the electrolyte react with the electrodes. This causes a difference in the amount of electrons between the two terminals. One terminal in a battery has mainly negative charges (electrons). The other terminal has mainly positive charges (Figure 11.10). The negative charges are electrons, which can move. They are attracted to the positive charges at the positive terminal. If a conductor, such as a copper wire, is connected to both terminals, then the electrons flow from the negative terminal to the positive terminal.

The difference in electric potential energy between two points in a circuit is called the potential difference or voltage ( V ) .

This difference causes current to flow in a closed circuit. The higher the potential difference in a circuit, the greater the potential energy of each electron.

–

–

–

++

++

++

++

++

++

++

Figure 11.10

An electrochemical cell or battery gives electrons electric potential energy.


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Measuring Potential Difference

The potential difference between two locations in a circuit is measured with a voltmeter . For example, you could place the connecting wires of the voltmeter across the positive and negative terminals of a battery like the rectangular yellow box shown in

Figure 11.11. The voltmeter would then display the potential difference of the battery. The SI unit for measuring potential difference is the volt (V) .

Figure 11.11

The orange device is a voltmeter. It is showing a reading of

1.50 V. The yellow device is a battery.

How Electrons Transfer Energy in a Circuit

When you turn on the light switch on a wall, you close the circuit and immediately the light comes on. How do the electrons get from the switch to the light bulb so fast? It may surprise you to learn that electrons do not travel from the switch to the bulb. You can picture electrons in a wire as being like water in a hose. If a hose connected to a tap already has water in it and you turn the tap on, water comes out of the end of the hose immediately.

Electrons in a wire work in a similar way. When an energy source is connected to a circuit, electrons in the conductor “push” or repel other electrons nearby. As soon as one electron starts to move at one end of the wire, it pushes the next one, which pushes the next one and so on. By pushing the first electron, you make the last electron move (Figure 11.12). That is why when you flip the switch, the light goes on instantly even though the electrons themselves have not moved from the switch to the light bulb.

Figure 11.12

Electrons in a wire are like marbles in a tube. If you push a marble at one end of the tube, the energy is transmitted through all the marbles. When electrons in a wire are “pushed” from one end, energy is transmitted all along the electrons in the wire.


1.

What is another name for stored energy?

2.

How is an apple falling from a tree like the potential difference in a battery?

3.

What does potential difference measure?

4.

What is another name for potential difference?

5.

When you walk into a dark room and turn the light on, do the electrons travel all the way from the switch to the light? Explain your answer.


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Current

Electric current is a measure of the amount of electric charge that passes by a point in an electrical circuit each second. Think of the continuous flow of electric current as being like water flowing in a stream. The water keeps on flowing unless its source dries up. As long as the battery continues to separate charges on its terminals, the electrons continue to flow. Because the current flows in only one direction it is called direct current (DC) .

The flow of current from batteries is DC, but the current that flows through cords plugged into the wall sockets in your home is called alternating current. Alternating current (AC) flows back and forth at regular intervals called cycles. This is the current that comes from generators and is carried by the big power lines to your home.

Measuring Current

Current in a circuit is measured using an ammeter, as shown in

Figure 11.13. The unit of electric current is the ampere (A) . An ampere is a measure of the amount of charge moving past a point in the circuit every second.


“Ampere” and “ammeter” are named in honour of André-Marie Ampère

(1775–1836), a French physicist who studied electricity and magnetism.

Figure 11.13

These ammeters show a reading of 0.50 A. The meter on the right has amperes on the scale below the black curved line.

Current Electricity and Static Electricity

Current electricity is different from static electricity because current electricity is the flow of electrons in a circuit through a conductor. Static electricity is the electric charge that builds up on the surface of an object. Static electricity discharges when it is given a path, but it does not continue to flow.


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Electron Flow and Conventional Current

Throughout this unit, we refer to current in terms of electrons flowing from a negative terminal to a positive terminal in a battery. However, when scientists studied electricity several hundred years ago, they did not yet know about electrons. They inferred that when electric current flowed from one object to another, it did so because one object had a greater amount of electricity, so the electricity flowed from the higher or more positive source to the lesser or more negative source. The mathematical equations and conventions developed afterward followed this assumption. This view is called conventional current, and it is a different way of describing the movement of electrons in a circuit (Figure 11.14).

(d)

– +

(a)

(c)

(b)

Figure 11.14

Conventional current describes current as leaving the source from the positive terminal (a) and entering the meter at its positive terminal (b). Then, the current is described as passing through the meter and leaving through the negative terminal (c). It then returns to the negative terminal of the source (d).

When you connect an ammeter or voltmeter to a circuit, you need to think in terms of conventional current rather than electron flow (Figure 11.15). There are two terminals on a meter that you use to connect to a circuit. The negative (–) terminal is often black, and the positive (+) terminal is often red. Always connect the positive terminal of the meter to the positive terminal of the electrical source. Connect the negative terminal of the meter to the negative terminal of the electrical source.

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Figure 11.15

When you connect an electrical meter, follow the rule “positive to positive, and negative to negative.” The positive red terminal of the meter is connected to the circuit. The positive red terminal of the battery is also connected to the circuit. The negative black terminals of the meter and the battery are connected directly.


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Resistance

Resistance is the degree to which a substance opposes the flow of electric current through it. All substances resist electron flow to some extent. Conductors, such as metals, allow electrons to flow freely through them and have low resistance values. Insulators resist electron flow greatly and have high resistance values. Resistance is measured in ohms ( ⍀ ) using an ohmmeter . An ohmmeter is a device for measuring resistance. An ohmmeter is usually part of a multifunctional meter called a multimeter (Figure 11.16).

When a substance resists the flow of electrons, it slows down the current and converts the electrical energy into other forms of energy. The more resistance a substance has, the more energy it gains from the electrons that pass through it. The energy gained by the substance is radiated to its surroundings as heat and/or light energy (Figure 11.17).

Figure 11.16

Multimeters can be used to measure potential difference, current, or resistance.

Figure 11.17

When electrons pass through a resistor, such as the element on this electric heater, their electrical energy is converted to heat and to light.

Resistance in a Circuit

The more resistance a component has, the smaller its conductivity.

For example, current in a circuit might pass through the filament in a light bulb (Figure 11.18). The filament is a resistor , which is any material that can slow current flow. The filament’s high resistance to the electron’s electrical energy causes it to heat up and produce light. filament


The symbol for ohm, ⍀ , is the Greek letter omega.

Figure 11.18

The filament in a light bulb is an example of a resistor.


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Figure 11.19

An electron entering a resistor is similar to a ball at the high end of a ramp, where potential energy is greater.

Figure 11.20

Resistors come in many shapes and sizes. The type of material the resistor is made from affects its resistance.




D15 Design a Lab on page 446

Resistors and Potential Difference

Resistors can be used to control current or potential difference in a circuit. When you work with resistors, you should always be aware that they can heat up and cause burns. Use caution when handling them.

In a circuit, electrons have a higher potential difference as they enter a resistor compared to when they leave the resistor because they use up some energy in passing through the resistor.

You can picture electrons entering a resistor as being at the high end of a ramp, where they have a lot of potential energy. In this analogy, electrons leaving the resistor are at the bottom end of the ramp, where their potential energy has been converted to another form of energy (Figure 11.19).

Types of Resistors

A wide variety of resistors are made for different applications, especially in electronics (Figure 11.20). For example, televisions contain dozens of different resistors.

Resistors can be made with a number of techniques and materials, but the two most common types are wire-wound and carbon-composition. A wire-wound resistor has a wire made of heat-resistant metal wrapped around an insulating core. The longer and thinner the wire, the higher the resistance.

Wire-wound resistors are available with values from 0.1 ⍀ up to

200 k ⍀ . The wire for a 200-k ⍀ resistor is very thin.

Carbon-composition resistors are made of carbon mixed with other materials. The carbon mixture is moulded into a cylinder with a wire at each end. By varying the size and composition of the cylinder, manufacturers produce resistances from 10 ⍀ to

20 M ⍀ . Moulded carbon resistors are cheaper to make than wirewound resistors but less precise.


1.

What is electric current?

2.

What does “resistance” refer to in terms of electron flow?

3.

Copy and complete the following table in your notebook. Some answers are provided for you.

Quantity

Potential difference

Abbreviation Unit Symbol ampere

⍀


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Resistance in a Wire

The flow of water in pipes is another useful model of electricity

(Figure 11.21). Not all pipes transport water equally well. The longer and thinner a pipe is, the more resistance it has to the flow of water. A pipe with a bigger diameter has less resistance, which allows a greater flow of water.

Similarly, the amount of resistance in a circuit affects the electrical current. For any given potential difference, current decreases if you add resistance. As with water flow, you get the least resistance with a short, wide path with no obstructions. The shorter and thicker the wire, the less resistance it creates for electrons. Other factors affecting the resistance of a wire include the material it is made from and its temperature, as shown in

Table 11.1.

Take It Further

A number of rechargeable dry cells are available, such as NiCd,

NiMH, and lithium ion. Research the different types of rechargeable dry cells. Compare their composition, lifetime, cost, and ability to hold charges. Begin your research at ScienceSource .

Figure 11.21

Resistance in a pipe reduces the flow of water. The smaller the pipe, the greater the resistance, so the flow is less. Resistance in a conductor reduces the flow of electrons.

Table 11.1

Factors Affecting the Resistance of a Wire

Factor

Material

Temperature

How Factor Affects Resistance

Silver has the least resistance but is very expensive to use in wires. Most conducting wires are made from copper.

As the temperature of the wire increases, its resistance increases and its conductivity decreases. In other words, a colder wire is less resistant than a warmer wire.

Length Longer wires offer more resistance than shorter wires. If the wire doubles in length, it doubles in resistance.

Cross-sectional area Wider wires offer less resistance than thinner wires. If the wire doubles in width, its resistance is half as great.

Conducting wires that carry large currents need large diameters to lessen their resistance.


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D13 Quick Lab

Make Your Own Dimmer Switch

Some homes have dimmer switches on their lights.

A dimmer switch allows you to adjust light levels in a room from nearly dark to very bright by moving a lever or turning a knob.

Purpose

To use resistance to control the amount of current flowing through a light bulb


• battery

• connecting wires with alligator clips

• flashlight bulb (2.5 W) and socket

• 40-cm of 32-gauge Nichrome™ wire

• piece of wood with screws (see Figure 11.22)

Procedure

1.

Connect the battery to the light bulb, and set up the Nichrome™ wire on the board as shown in

Figure 11.22. Make sure the Nichrome™ wire is connected at one end but not the other, leaving your circuit open. Have your teacher approve your set-up before you proceed further.

2.

Close your circuit by connecting the other end of the Nichrome™ wire, maximizing the length of the wire in the circuit. Note the brightness of the bulb (Figure 11.22(a)).

3.

Move the alligator clips on the Nichrome™ wire closer together (Figure 11.22(b)). Note the brightness of the bulb.

4.

Continue to observe the brightness of the bulb as you move one of the alligator clips along the

Nichrome™ wire.

Questions

5.

(a) How did the brightness of the bulb change as you moved the alligator clips?

(b) Explain why the brightness changed as the length of wire changed.

6.

How do your observations in this activity help explain how a dimmer switch works?

(a) (b)

Figure 11.22

The brightness of the bulb changes, depending on whether the space between the clips on the wire is

(a) larger or (b) smaller.


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D14 Quick Lab

Modelling Potential Difference, Current, and Resistance

A model in science can help you picture a process or object that may be hidden from view or that may be too large or too small to view directly. You can also use a scientific model to help you communicate your ideas.

Purpose

To model interactions among potential difference, current, and resistance using water flowing in a hose


• 50-cm or longer length of rubber tubing

• water tap and sink or bucket

Procedure

• 1000-mL beaker or bucket

• stopwatch

1.

Create a data table with headings like the ones shown below. Give your data table a title.

2.

Attach one end of the tubing to a tap. Place the other end of the tubing in a bucket or sink as far from the tap as the tubing will reach without bending.

3.

Turn on the cold water to a medium flow. Record the time it takes for water to exit the tubing.

4.

Pinch the end of the tubing, and then turn off the water. Keep the end pinched. Empty the bucket (if using) when you have finished timing.

5.

Turn on the cold water to a midway point, and release the end of the tubing at the same time.

Record the time it takes for water to exit the tubing into the sink or bucket.

6.

While the water is running, pinch the end of the tubing slightly. Observe what happens to the flow. Empty the bucket (if using) when you have finished timing.

7.

Record the time it takes to fill the beaker or bucket using the slightly pinched length of tubing. Empty the container when you have finished timing.

8.

Record the time it takes to fill the beaker or bucket using an open length of tubing.

9.

Record the time it takes to fill the beaker or bucket using an open length of tubing and the water turned on full. Empty the container when you have finished timing.

10.

Follow your teacher’s instructions for cleaning up.

Questions

11.

(a) How did the exit times compare for the tubes in step 3 and step 5?

(b) How would you explain any difference in times?

12.

What part of this activity modelled electric current in a circuit?

13.

(a) How does the size of the opening in the tubing affect water flow?

(b) Relate the size of the opening of the tubing to resistance in wires.

14.

(a) How does how far a tap is opened affect water flow through the tubing?

(b) Relate how far a tap is opened to potential difference in a circuit.

Time to Exit Empty

Tube (s)

Time to Exit

Pinched Tube (s)

Time to Fill Beaker or Bucket with

Pinched Tube (s)


Open Tube (s)


Water on Full (s)


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D15 Design a Lab

Investigating Conductivity

Question

How does the conductivity of different solutions compare?


• 100-mL graduated cylinder

• 250-mL beaker

• distilled water

• conductivity tester

• tap water

• salt water

• vinegar

• copper(II) sulphate solution

• other solutions provided by your teacher

Figure 11.23

Conductivity tester

Procedure

Part 1

1.

Read through the procedure. Then, design a data table to record your predictions and your conductivity readings of the solutions you will test. Give your table a title.

2.

Predict which solutions will be the best conductors and which will be the poorest conductors. Record your predictions and the characteristics on which you are basing your predictions.

3.

Put 50 mL of distilled water into a 250-mL beaker.



Using equipment, materials, and technology accurately and safely

Adapting or extending procedures

4.

Place the metal tips of the conductivity tester in the distilled water (Figure 11.23). Record the conductivity reading of the distilled water in your table. If your conductivity tester is a light bulb, describe the brightness of the bulb.

5.

Repeat steps 3 and 4 with 50-mL samples of tap water, salt water, vinegar, copper(II) sulphate solution, and any other solutions your teacher provides for you to use. After each conductivity measurement, empty the beaker as directed by your teacher and rinse it with distilled water.

Also, wipe off the tips of the conductivity tester.

Make sure that you insert the tips to the same depth in each solution.

6.

Clean up your work area. Make sure to follow your teacher’s directions for safe disposal of materials. Wash your hands thoroughly.

Part 2

7.

Plan an investigation to compare the conductivity of other solutions. Have your teacher approve your plan, and then conduct your investigation.


8.

How did you determine whether there were differences in conductivity between the solutions you tested?

9.

Rank the substances in order of high conductivity to low conductivity.

10.

How did your results compare with your predictions?

Skill Practice

11.

Make an hypothesis about why there were differences in conductivity between the solutions.


12.

Write a summary of your results that answers the question “How does the conductivity of different solutions compare?”


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11.1



1.

(a) Describe the two main components of an electrochemical cell.

(b) How does a wet cell produce electricity?

2.

What direction do electrons flow in a circuit?

3.

(a) What device measures potential difference?

(b) What are the units for measuring potential difference?

4.

(a) What device measures current?

(b) What are the units for measuring current?

5.

What is the difference between potential difference and current?

6.

What is the difference between DC electricity and AC electricity?

7.

(a) What is the function of an electrical load in a circuit?

(b) List four examples of electrical loads.

8.

What does resistance refer to in a circuit?

9.

What is the role of a resistor in a circuit?

10.

What are four factors affecting resistance in a wire?


11.

Why must a circuit be closed in order for a current to flow?

12.

Use a three-circle Venn diagram to compare and contrast alternating current, direct current, and static electricity.

Quit

13.

Make a list of similarities between the flow of water and an electric circuit.

14.

A student is planning to test several different electrode combinations to see which would produce the greatest potential difference in a wet cell. State whether each of her choices will work. Explain why or why not. Her choices for electrodes are as follows:

(a) both zinc

(b) zinc and copper

(c) both copper

15.

The illustration below shows a design for a dry cell. How does this design differ from the dry cell shown in Figure 11.6 on page 435?

insulator insulated casing positive terminal zinc can

(negative electrode) negative terminal insulator

Question 15 electrolyte paste carbon electrode

Reflection

16.

What do you now understand about current electricity that you did not know before reading this chapter?



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11.2

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Series Circuits and Parallel Circuits


• A circuit diagram represents an electric circuit.

• An ammeter is hooked up in series to measure current.

• A voltmeter is hooked up in parallel to measure voltage.

• In a series circuit, the current is constant and the voltages across resistors add up to the total voltage.

• In a parallel circuit, the voltages are constant and the currents on each path add up to the total current.

Figure 11.24

These toy robot dogs are controlled by electric circuits.

Designing Circuits

Computers and the toy robots in Figure 11.24 have complex circuits. Other electrical devices such as a flashlight or a hair dryer have much simpler circuits. The simplest circuit is a loop.

An ordinary flashlight can be designed this way. If you take a flashlight apart, you will probably find a light bulb, some wire, a couple of batteries, and a plastic casing to hold and protect the electrical parts. This design works very well for providing light when it is dark. It also works well in terms of cost. Flashlights are easy to build with readily available materials and can be assembled efficiently.

A simple loop isn’t always the best design when there are a variety of different components in the circuit. Designers have to ensure that one component does not depend on another. For example, it would be very frustrating to the user if the toy robot stopped working because one of its light bulbs went out. You would probably be upset if your computer at school stopped working because an LED indicator burnt out. In these devices, multiple electrical loops are used so that if one component stops working, the rest of the device will continue to function.


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Tiny Circuits

Conventional switches and other electrical components are practical and convenient for homes or simple electrical devices.

But for the miniature circuits in advanced electronic devices such as computers, transistors must be used instead. A transistor is a tiny device that acts as a switch or amplifier in a circuit.

Transistors are often referred to as solid-state components because they are made of solid material with no moving parts.

Most transistors are constructed with three layers of specially treated silicon. These layers are arranged so that a small potential difference through the middle layer controls a current between the outer layers. In this way, transistors can act as switches.

Microcircuits (also called integrated circuits) are made up of microscopic transistors and other electrical devices. A microcircuit is exactly what its name suggests: a circuit on an extremely small scale. Microcircuits regularly contain more than a million components per square centimetre (Figure 11.25).

Figure 11.25

A microcircuit is usually called a “chip” or a

“microchip.”

D16 Quick Lab

Keep the Lights On

Current flows when a circuit is complete. If there is a break in a circuit, due to a burned-out bulb, for example, the current cannot continue. In this activity, you will investigate how to keep current flowing through a circuit even though one bulb may be burned out or missing.

Purpose

To compare the flow of electrons in two different circuits


• 1 D dry cell

• 5 insulated copper wires with both ends bare

• three 2.0-V flashlight bulbs

CAUTION: Open the circuit if the wires get hot.

Procedure

1.

Circuit A: Using any of the materials, hook up three bulbs in a row so they all light up. Make a labelled diagram of your set-up.

2.

Circuit B: Hook up all three bulbs so that you can remove one bulb without disconnecting the wires and still have the other bulbs stay on. Make a labelled drawing of your set-up.

Questions

3.

(a) What would happen to the other two bulbs if you removed one bulb in Circuit A?

(b) Why would this happen?

4.

Why did the other two bulbs stay lit when you removed one bulb in Circuit B?

5.

Draw a circuit that would allow you to remove two bulbs and yet have the third bulb stay lit. Have your teacher approve your drawing. If time allows, test your ideas by building the circuit.


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Figure 11.26

The four basic parts of a circuit

Circuit Diagrams

Engineers and designers of electrical circuits use special symbols that show the components and connections in a circuit. These symbols make it easier to plan and analyze a circuit before you build aggrra m.

You can use the symbols in Table 11.2 to draw and interpret circuit diagrams (Figure 11.26). Knowing the basic circuit symbols can help you analyze existing circuits and make it easier to understand where the current flows and how a device functions.

Follow these rules when you draw circuit diagrams.

• Always use a ruler to draw straight lines for the conducting wires.

• Make right-angle corners so that your finished diagram is a rectangle.

Table 11.2

Circuit Symbols

Symbol Component wire

Function conductor; allows electrons to flow cell, battery electrical source; longer side is the positive terminal, shorter side is the negative terminal lamp (light bulb) specific load; converts electricity to light and heat resistor general load; converts electricity to heat switch opens and closes the circuit ammeter voltmeter measures current through a device, connected in series measures voltage across a device, connected in parallel


1.

What is a circuit diagram?

2.

What are two rules you should follow when you draw a circuit diagram?

3.

Draw the circuit symbol for:

(a) a light bulb

(b) an ammeter

(c) a voltmeter

4.

Draw a circuit diagram for a circuit that includes a resistor, a switch, conducting wires, and a battery.


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Series Circuits

are arranged one after another in series (Figure 11.27). A series circuit has only one path along which electrons can flow. If that pathway is interrupted, the whole circuit cannot function.

The amount of current is the same in all parts of a series circuit. However, if you add more resistors, you increase the total resistance of the circuit. This decreases the current. Adding an extra bulb to a series string of lights makes all the bulbs dimmer.

Electrons use up all their potential difference going around a series circuit no matter how many loads are in the circuit. For example, the electrons that leave a 12-V battery will “lose” all

12 V before they return to the battery. Each load will use part of the total potential difference, depending on how much it resists the flow of electrons.

Figure 11.27

A series circuit has only one path along which current can flow. junction point

Parallel Circuits

arranged so that electrons can flow along more than one path

(Figure 11.28).

The points where a circuit divides into different paths or where paths combine are called junction points. An interruption or break in one pathway does not affect the other pathways in the circuit. Similarly, adding a new pathway with more resistors does not affect the resistance in any of the other pathways. In fact, adding extra resistors in parallel decreases the total resistance of the circuit. This might seem strange, but think about how much less resistance there is when you drink through two straws instead of one.

Most electrons will follow the path with the smallest resistance values. Therefore, the amount of current is greater on the paths with the smaller resistances (Figure 11.29).

Each electron has the same amount of energy, and electrons must expend all their energy on the path they are on. This is why the potential difference across parallel resistors will always be the same, even though the resistors themselves are of different values.

Table 11.3 on the next page summarizes the characteristics of current and potential difference in series and parallel circuits.

Figure 11.28

In a parallel circuit, each component has its own path for current.

3.0 A

2.0 A

1.0 A

6.0 A

Figure 11.29

Loads of different resistance that are connected in parallel have different currents.


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Table 11.3

Potential Difference, Current, and Resistance in Series and Parallel Circuits

Circuit Potential Difference Current Resistance

Series circuit Each load uses a portion of the total potential difference supplied by the battery.

Parallel circuit Each load uses all the potential difference supplied by the battery.

The current is the same throughout a series circuit.

The current divides into different paths. A pathway with less resistance will have a greater current.

The current decreases when more resistors are added.

Adding resistors in parallel decreases the total resistance of the circuit.





Figure 11.30

A combination circuit.

The switch in this circuit can turn all the bulbs on or off.

Two Types of Circuits

What happens when one light bulb burns out in a long string of decorative lights? If the set of lights is wired in series, the current must flow through one light before it gets to another light. When one light burns out, all lights go out because the current cannot flow past a burned-out bulb.

If the set of lights is wired in parallel, the current takes several different paths. If a light on one path goes out, current does not flow on that path. However, there are other paths where the current does flow and lights on those paths remain lit.

Series circuits and parallel circuits make up the circuits in your home and school. Some circuits are combinations of series circuits and parallel circuits (Figure 11.30). These combinations help prevent problems such as the refrigerator turning off because a light bulb burned out in a bedroom. It is an important safety feature in a combination circuit to have some switches wired in series, because it is sometimes necessary to turn off the electricity in part or all of a home (Figure 11.31).

Figure 11.31

A typical home has many parallel circuits.


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1.

Draw a circuit diagram of a series circuit with a battery, connecting wires, and one light bulb.

2.

Draw a circuit diagram of a parallel circuit with a battery, connecting wires and two light bulbs.

3.

What happens to the voltage in a series circuit when more loads are added?

4.

What happens to the current in a parallel circuit when more loads are added?

5.

How do combination circuits help prevent problems in circuits in a home?

Take It Further

A microcircuit is an extremely small circuit that may contain more than a million parts in a square centimetre. Find out how these tiny circuits are controlled and used. Begin your research at

ScienceSource .

D17 Quick Lab

Off and On

Suppose that all the lights in your home were connected in one simple circuit. When you closed a switch, every light would come on. When you opened the switch, every light would turn off. This arrangement would not be very practical for most uses. Instead, lights can be connected in a circuit in such a way that some can be turned on while others are turned off. In this activity, you will investigate how to create such a circuit.

Purpose

To design and build a circuit that can have lights turned on and off individually


• 3 or more flashlight bulbs with holders

• connecting wires

• 3 D dry cells

• switches for each light

CAUTION: Open the circuit if the wires get hot.

Procedure

1.

Circuit A: Design and draw a circuit diagram where the three bulbs can be either all on or all off.

2.

Circuit B: Design and draw a circuit diagram where each of the three bulbs in the circuit can be turned off and on individually.

3.

Circuit C: Design and draw a circuit diagram where two bulbs can be turned off while one stays on.

4.

Have your teacher approve your three circuit diagrams. Then, hook up the circuits and test whether they work.

5.

Clean up your work area.

Questions

6.

For each circuit, describe whether the lights were hooked up in series, in parallel, or in a combination.

7.

Was the brightness of the lights affected by changing how the bulbs were hooked up?

Explain.


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D18 Skill Builder Activity

Using Equipment Accurately and Safely

Part 1 — Measuring Current

Measuring current involves measuring the amount of charge passing a given point per second. The current is fed directly into the ammeter or multimeter where it is counted and then let back out into the circuit. The ammeter is hooked in series into the circuit, then the circuit is reconnected and the measurement is taken.

Follow these steps to hook up the ammeter.

1.

Attach a battery and three resistors in series.

Open the circuit.

2.

Hook your ammeter in series next to the positive side of the battery. Be sure to connect the positive (red) terminal of the ammeter to the positive (+) terminal of the battery. Connect the negative (black) terminal of the ammeter to the negative (–) terminal of the battery.

3.

Set the meter on the highest setting, and then lower the setting until you have the highest possible reading. Record the reading.

4.

Open the circuit and move the ammeter to immediately beyond the first resistor. Repeat steps 2 and 3.

5.

Repeat step 4 for each resistor.

CAUTION: Open the circuit if the wires and resistors get hot.

Part 2 — Measuring Voltage

6.

To insert a voltmeter in a circuit, simply connect the two wires from the terminals of the voltmeter to opposite sides of the component for which you want to measure the voltage (Figure 11.32).

7.

To find the voltage across an electrical source, connect the meter by attaching the red lead to the positive terminal and the black lead to the negative terminal. This allows you to take a reading on both sides of the source. The meter indicates the change in voltage.

8.

To find the voltage across a resistor or load in a circuit, connect a lead to each side of the resistor. Connect the black lead closest to the negative side of the source and the red lead closest to the positive side of the source. This method of connection is called connecting in parallel. By measuring voltage across the resistor, you are measuring the voltage drop as the current moves through the resistor.

9.

Your teacher will provide you with various types of dry cells and batteries. Use the voltmeter to test and report on the voltage of each cell and battery. Compare your readings with the voltage numbers that are written on their labels. If a multimeter is available, use it to repeat your measurements and then compare the results.

10.

Hook two or three dry cells in series. Do this by placing them end to end with the positive end of one dry cell touching the negative end of the other dry cell. Predict the voltage reading, and then use the voltmeter to see if your prediction was correct.

11.


Figure 11.32

A voltmeter connected across a resistor


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Series Circuit Analysis



Planning for safe practices in investigations

Gathering, organizing, and recording relevent data from inquiries

Question

What are the properties of a series circuit?


• 6.0-V battery

• three 100-

⍀ resistors

• switch

6.0 V

V

• multimeter (or voltmeter and ammeter)



Procedure

Part 1 — Measuring Voltage and Current

1.

Create a data table similar to the one below. Give your table a title.

Power

Supply

Resistor

1

Resistor

2

Resistor

3

Part 1:

Current

Voltage

Part 2:

Current

Voltage

2.

Construct the circuit shown in Figure 11.33.

Keep the switch open until your teacher approves your circuit. Then close the switch and record the current coming out of the power supply.

A resistor 1 resistor 2 resistor 3

Figure 11.33

Construct this circuit in step 2.

3.

Record the voltage across each resistor and the power supply.

4.

Open the switch, and move the ammeter to a position between the first two resistors. Close the switch, and record the current coming out of resistor 1.

5.

Open the switch, and move the ammeter to a position between the second and third resistors.

Close the switch, and record the current coming out of resistor 2.

6.

Open the switch, and move the ammeter to a position between the third resistor and the source. Close the switch, and record the current coming out of resistor 3.

Part 2 — Changing Resistance

7.

Open the switch, and remove one resistor. Close the switch. Measure and record the current.

8.

Measure and record the voltage across the power supply and across each of the two resistors.


9.

State what you noticed in Part 1 about the:

(a) current across the resistors in all cases

(b) sum of all voltages across the resistors

10.

State what happened in Part 2 to:

(a) the current

(b) the voltages across each resistor

(c) the sum of the voltages across the resistors

11.

What is the effect of adding an identical load in series in a simple circuit?

Skill Practice

12.

Did the voltages across any resistors equal the total voltage provided by the source? Explain why they did or did not.


13.

In a paragraph, summarize the properties of a series circuit.


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Parallel Circuit Analysis

Question

What are the properties of a parallel circuit?



Selecting instruments and materials

Observing, and recording observations


• 6.0-V dry cell

• three 100⍀ resistors


• switch

• multimeter (or voltmeter and ammeter)


Procedure

Part 1 — Potential Difference and

Current Measurements

1.

Create a data table similar to the one below. Give your table a title.

Power

Supply

Resistor

1

Resistor

2

Resistor

3

Part 1:

Current

Voltage

Part 2:

Current

Voltage

2.

Construct the circuit shown in Figure 11.34.

Keep the switch open until your teacher approves your circuit. Then, close the switch and record the current coming out of the power supply.

6.0 V

A

V

Figure 11.34


3. Record the voltage across each resistor and the power supply.

4. Open the switch, and move the ammeter to a position between the first two resistors. Close the switch, and record the current coming out of resistor 1.

5.

Open the switch, and move the ammeter to a position between the second and third resistors.

Close the switch, and record the current coming out of resistor 2.

6.

Open the switch, and move the ammeter to a position between the third resistor and the source. Close the switch, and record the current coming out of resistor 3.

Part 2 — Changing Resistance

7.

Open the switch, and remove one resistor. Close the switch. Measure and record the current.

8.

Measure and record the voltage across the power supply and across each of the two resistors.


9.

State what you noticed in Part 1 about the:

(a) current across the resistors in all cases

(b) sum of all voltages across the resistors

10.

State what happened in Part 2 to:

(a) the current

(b) the voltages across each resistor

(c) the sum of the voltages across the resistors

11.

What is the effect of adding an identical load in parallel in a simple circuit?

Skill Practice

12.

Did the voltages across any resistors equal the total voltage provided by the source? Explain why they did or did not.


13.

In a paragraph, summarize the properties of a parallel circuit.


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11.2



1.

Copy and complete the following chart in your notebook.

Voltage and Current in Circuits

In a Series

Circuit

Voltage

Current

In a Parallel

Circuit

2.

(a) Draw a circuit diagram of the circuit shown here.

(d)

– +

(a)

(c)

(b)

Question 2

(b) Is this a series circuit or a parallel circuit?

(c) How do you know?

3.

What is the voltage across the source in each of these circuits?

(a)

(b)

2.0 V 4.0 V 6.0 V

12 V 12 V 12 V

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4.

(a) Draw a circuit diagram that shows three resistors in series.

(b) Draw a circuit diagram that shows three resistors in parallel.

(c) Draw a circuit diagram that shows one resistor in series and two resistors in parallel.

5.

Suppose two pathways in a parallel circuit have different resistances. Will the current in each pathway be the same? Explain.


6.

You have three light bulbs, each with a different resistor. The amount of current through a bulb will affect how much light it emits.

(a) Will the order in which you hook up the light bulbs in series affect the intensity of light each emits? Explain.

(b) What happens when you hook up the bulbs in parallel?

7.

Electrons in a circuit can be compared to a group of shoppers who go out to spend money in shops. Use this analogy or create one of your own to explain the following.

Include a labelled diagram as part of your answer for each one.

(a) potential difference, current, and resistance in a series circuit

(b) potential difference, current, and resistance in a parallel circuit

Reflection

8.

What images or memory aids help you remember the differences between series and parallel circuits?



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11.3

Ohm’s Law


• Ohm’s law, V = IR, describes the relationship between potential difference, current, and resistance.

• In a short circuit, the current does not take the intended path back to its source.

• Fuses and circuit breakers are safety devices.

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Figure 11.35

Potential difference, current, and resistance have the same relationship in microcircuits in a computer circuit board like this one as they do in the wiring in homes and offices.

Figure 11.36

Georg Ohm (1789–1854)

A Fascination with Electricity

The circuit boards in the computers you use work because of the relationships between potential difference, current, and resistance

(Figure 11.35). These relationships have been understood for about

200 years because of the work of Georg Ohm.

Georg Simon Ohm (Fig 11.36) was like any German boy in the early 1800s. At the local high school, he studied physics, chemistry, math, and philosophy. He spent most of his free time playing billiards, ice skating, and dancing with his friends. No one imagined that one day he would be a famous name in science.

His journey to discovering a scientific law began after graduation when he went to a private school in Switzerland to teach. Here Ohm taught mathematics, but secretly he dreamed of studying with great mathematicians at an important university.

To achieve his dream, he continued to study mathematics and teach. One day, he was asked to instruct in the electricity labs.

This day was a turning point in Georg Ohm’s life. Fascinated by electricity, he immersed himself in the study of the characteristics of potential difference, current, and resistance.


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Ohm’s passion and commitment to his studies led to a deep understanding of how these different electrical concepts were related. Much of what he discovered you have already learned in this unit. He stated these discoveries in what is today called

Ohm’s law.

A law in science is a generalization based on collection of observable evidence. It is the conclusion of this evidence and can be defended by repeating a variety of experiments over many years. A scientific law becomes accepted by the scientific community as a description of our natural world.

Ohm’s law established the relationships between potential difference ( V), current (I), and resistance (R). The symbol for resistance is called the ohm ( ⍀ ) in honour of Georg Ohm’s work in this field.


The symbol “ I ” is used for current because it stands for “intensity.”

D21 Quick Lab

Potential Difference, Current, and Resistance

Using the equipment available in your science class, you can investigate the same relationships between potential difference, current, and resistance that

Georg Ohm did over 200 years ago.

Purpose

To observe how potential difference, current, and resistance are related


• 1.5 V dry cell

• resistors, any values from 15 ⍀ to 50 ⍀


• switch

• multimeter or voltmeter and ammeter

1.

2.

Trial Resistance

( ⍀ )

Current

(A)

Potential

Difference

(V)

Resistance ⴛ Current

Procedure

1.

Create a table like the one below to record the data you will collect. Give your table a title.

2.

Connect one resistor into a simple circuit. If you are using a voltmeter and ammeter, connect these devices as well. Keep your circuit open until your teacher has approved your set-up.

3.

Close your circuit.

4.

Measure and record the voltage across the resistor.

5.

Measure and record the current through the resistor.

6.

Record the resistance of the resistor you used.

7.

Repeat steps 2 to 6.

8.


Question

9.

Multiply the resistance by the current for each of the trials you completed. What can you infer from your answers?


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V V

I

V = IR

Figure 11.37

Ohm’s law states that potential difference ( V) equals current ( I) times resistance (R).




R


Georg Ohm described how potential difference and current are affected when one of the values is changed. He realized that the potential difference ( V ) in a circuit is equal to the current ( I ) multiplied by the resistance ( R ). Ohm’s law states that, as long as temperature stays the same, V = IR (Figure 11.37). In other words:

• the resistance of a conductor remains constant

• the current is directly proportional to the potential difference

Table 11.4 and the following examples show how to use

Ohm’s law to calculate unknown quantities.

Table 11.4

Ohm’s Law

Known

Quantity

Current, resistance

Potential difference, resistance

Potential difference, current

Symbol

IR

VR

VI

Unknown

Quantity potential difference current I

Symbol

V resistance R

Unit

V

A

⍀

Equation

V = IR

I = V

R

R = V

I

Practice Problems

1.

A current of 1.5 A flows through a 30-

⍀ resistor that is connected across a battery. What is the battery’s voltage?

2.

If the resistance of a car headlight is 15

⍀ and the current through it is

0.60 A, what is the voltage across the headlight?

3.

The current in a circuit is

0.50 A. The circuit has two resistors connected in series: one is 110

⍀ and the other is 130

⍀

. What is the voltage in the circuit?

Example Problem 11.1


⍀ resistor in a circuit.

What is the voltage?

Given

Current I = 4.0 A

Resistance R = 40

⍀

Required

Voltage V = ?

Analysis and Solution

The correct equation is V = IR.

Substitute the values and their units, and solve the problem.

V = IR

= (4.0 A)(40

⍀

)

= 160 V

Paraphrase

The voltage in the circuit is 160 V.


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A 30-V battery generates a current through a 15⍀ resistor.

How much current does the battery generate?

Given

Voltage V = 30 V

Resistance R = 15 ⍀

Required

Current I = ?


The correct equation is I = V .

R

Substitute the values and their units, and then solve the problem. I = V

R

=

30 V = 2 A

15 ⍀

Paraphrase

A current of 2 A is generated.


1.

A firetruck has a searchlight with a resistance of 60

⍀ that is placed across a 24-V battery. What is the current in this circuit?

2.

A bulb of 15-

⍀ resistance is in a circuit powered by a 3-V battery. What is the current in this circuit?

3.

What would the current be in question 2 if you changed to a 45-

⍀ bulb?


An electric stove is connected to a 240-V outlet. If the current flowing through the stove is 20 A, what is the resistance of the heating element?

Given

Voltage V = 240 V

Current I = 20 A

Required

Resistance R = ?


The correct equation is R =

V

I

.

Substitute the values and their units, and then solve the problem.

R = V

I

=

240 V = 12

20 A

⍀

Paraphrase

The resistance of the heating element is 12

⍀

.


1.

A current of 0.75 passes through a flashlight bulb that is connected to a

3.0-V battery. What is the bulb’s resistance?

2.

A current of 625 mA runs through a bulb that is connected to a 120-V power supply. What is the resistance of the bulb?

3.

A table lamp draws a current of 200 mA when it is connected to a 120-V source. What is the resistance for the table lamp?


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During Reading

Definitions in Context

Often, unfamiliar terms are defined right in the text that you are reading. You don’t need to look them up in a glossary or dictionary. Look for the boldfaced words, and then find the definition in the sentence either before or after the term.

Add words and definitions to your personal list of terms.

Home Quit

Ohm’s Law and Temperature

Ohm’s law works for most circuits. However, temperature affects resistance. Generally, resistance is lower when a conductor is cooler. As the temperature increases, resistance increases. For example, a filament in an incandescent light bulb often has 10 times its normal current flowing through it at the instant it is switched on. This current heats the filament white-hot in a fraction of a second. The huge rise in temperature greatly increases the filament’s resistance, which reduces the current flowing through it. Light bulb filaments sometimes burn out when they are switched on because of the sudden temperature change and other forces caused by the large initial current.

short circuit

Figure 11.38

Current can flow more easily through the wire path than through the light bulb. This creates a short circuit, which could be dangerous.

Short Circuits

Sometimes a wire’s insulation breaks down or another problem develops that allows electrons to flow through a device along a different path than the one intended. The device develops a short circuit . A short circuit is an accidental low-resistance connection between two points in a circuit, often causing excess current flow

(Figure 11.38). Not only do short circuits mean that your electrical device will not work, they can also be dangerous. The conducting wires can quickly become hot and can start a fire.

One danger from short circuits occurs when a transmission line has been knocked down in a storm. Without a complete path, the electricity cannot flow. However, if you come in contact with the wire, the electricity will take a path through your body to the ground and seriously injure or kill you. The driver shown in

Figure 11.39 is safe as long as he is inside the truck. If he has to leave, he would need to jump free, not step out. He has to jump so he does not provide a path for the electricity to flow through him to the ground.

There are times when a technician must short out part of a circuit intentionally by connecting a wire across a load in parallel.

The low-resistance wire causes the current to flow through it rather than through the higher resistance device. This allows the technician to work on the device without interrupting the rest of the circuit.

Figure 11.39

The driver should stay in the truck and wait for help.


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Electrical Safety

All electrical appliances present a risk of electric shock. Always handle electrical appliances properly and observe all safety precautions. Be careful to disconnect the plug before handling an appliance. Some electronic devices, such as computers, retain electric charge even when they are unplugged

(Figure 11.40). This is why many electrical devices have a “Do Not Open” warning printed on them. Take the warning seriously, and do not attempt to repair the device yourself. Instead, contact a repair technician.

Fuses and Circuit Breakers

In electric circuits in your home, fuses and circuit breakers act as a first line of defence if something goes wrong. A fuse is a safety device in an electric circuit that has a metallic conductor with a low melting point compared to the circuit’s wires

(Figure 11.41). If the current gets too high, the metal in the fuse melts and the current flow stops. This prevents further problems, such as damage to your electrical components or a possible fire. A blown fuse must be physically replaced as it can work only once.

The symbol represents a fuse in a circuit diagram.

A circuit breaker does the same job as a fuse except that the wire inside does not melt.

Instead, the wire heats up and bends, which triggers a spring mechanism that turns off the flow of electricity. Once the breaker has cooled, it can be reset. Older homes and apartment buildings tend to have fuse panels, whereas modern buildings have breaker panels (Figure 11.42).

Figure 11.40

Some electronic devices, such as this computer, store electrical energy even when the device is not plugged in.

Figure 11.41

Examples of fuses. A normal current can pass through a fuse, but a higher than normal current or short circuit will melt the metal in the fuse.

Figure 11.42

Circuit breakers help prevent electric overloads.


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Take It Further

Diodes are devices that allow electric current to flow in one direction but not in the opposite direction. Find out how diodes are used in microcircuits and other circuits. Start your research at

ScienceSource .

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Three-Prong Plug

Another safety feature is the three-prong electrical plug shown in

Figure 11.43. The third prong of a three-prong electrical plug connects the device to the ground wire of the building. The ground wire sends any unwanted current flow directly to the ground. Instead of electricity travelling to the metal body of the device and shocking a person using the device, the current is directed to the ground.

Ground Fault Circuit Interrupter

Some appliances and devices have an added safety feature. A ground fault circuit interrupter (GFCI) or residual current device is a device that detects a change in current and opens the circuit, stopping current flow (Figure 11.44). For example, if an appliance gets wet while you are handling it and some current starts to flow through the water, the GFCI opens the circuit so there is less chance of injury to you. Remember, it is extremely dangerous to use any electrical device around water, including radios or televisions.

Figure 11.43

One prong in a three-prong plug carried the current to the load, another prong returns the current to the source, and the third prong directs the current to the ground in the case of a short circuit.

Figure 11.44

Ground fault circuit interrupters are part of some electric sockets.


Electrical Safety

Imagine you have just been hired as a consultant by the Electrical Safety Authority of Ontario to help create awareness of electrical safety for kindergarten students.

1.

Work alone, with a partner, or in a small group to create an electrical safety poster or brochure that can be shared with a kindergarten class. Be sure to choose electrical safety points that are relevant to young children and to communicate them in an engaging way.


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Investigating Ohm’s Law

Question

How are potential difference, current, and resistance related?


• four 1.5-V dry cells


• voltmeter, ammeter

• switch

• 2 different resistors between 100 ⍀ and

300 ⍀

CAUTION: Disconnect the circuit if the wires or resistors get hot.

Procedure

1.

Set up a data table like the following. Fill in the resistor value for the two resistors you will be using. Examples below are 100 ⍀ and 200 ⍀ .

Give your table a title.

1.5 V

3.0 V

4.5 V

6.0 V

Resistor

( ⍀ )

1. 100

2. 200

1. 100

2. 200

1. 100

2. 200

1. 100

2. 200

Voltage

(V)

Current

(A)

Calculated

Resistance

2.

Construct the following circuit using resistor 1 and one 1.5 V dry cell (Figure 11.45).

Skills References 2, 10


Interpreting data/information to identify patterns or relationships

Drawing conclusions

3.

Have your teacher approve your circuit, and then close the switch. Quickly measure and record current and voltage. Open the switch.

4.

Replace resistor 1 with resistor 2. Repeat step 3.

5.

Connect a second 1.5-V dry cell in series with the first cell in the circuit. Repeat steps 3 and 4, measuring current and voltage for each resistor.

6.

Connect a third 1.5-V dry cell into the circuit.

Repeat steps 3 and 4.

7.

Connect a fourth 1.5-V dry cell. Repeat steps 3 and 4.

8.

Calculate your measured resistance for each

.

resistor using R = V

I


9.

(a) How did your calculated values for resistors compare with their actual values?

(b) Explain possible reasons for any difference between the two values.

10.

Compare your data for all resistor 1 trials. When voltage is increased across a resistor, what happens to the current?

11.

Compare your data for all resistor 2 trials. When voltage is increased across the resistor, what happens to the current?

Skill Practice

12.

What would happen to the current values if you used a resistor with double the value of resistor 2?


13.

Describe the relationship between potential difference, current, and resistance.

A

V

Figure 11.45



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Resisting the Flow

Question

Do different materials have different values of electrical resistance?

Home Quit



Justifying conclusions

Identifying sources of error



• D cell and holder

• voltmeter

• ammeter or current sensor

• 10-cm length of solid graphite (pencil lead)

• 10-cm length of copper wire

• 10-cm length of

Nichrome™ wire

• 10-cm length of rubber tubing

• optional: 10-cm lengths of various other materials

• calculator

CAUTION: Open the circuit if the wires or the resistors get hot.

Procedure

1.

Make a table for recording your data (Figure

11.46). The table should include these headings:

Substance, Length Connected (10 cm or 1 cm),

Voltage (from step 2), Current, and Resistance. In the “Resistance” column, you will calculate the resistance for each observation. Give your table a title.

2.

Use connecting wires to connect each end of a D cell to a terminal on the voltmeter. Record the voltmeter reading in your table. Disconnect the voltmeter.

3.

Connect one wire from the D cell to a terminal of the ammeter (or current sensor). Attach another connecting wire to the other terminal of the ammeter.

4.

Clip the free ends of the connecting wires onto the ends of a 10-cm length of solid graphite.

Record the reading on the ammeter.

5. Move the clips on the graphite so that they are

1.0 cm apart. Record any change in the reading.

Figure 11.46

Determining resistance

6.

Repeat steps 4 and 5 for the copper wire,

Nichrome™ wire, rubber tubing, and the other materials.

7.



V

8.

Use Ohm’s law R = to calculate the

I resistance for each current recorded in your table.

9.

(a) Which substance had the greatest resistance?

(b) Explain any differences in resistance among the materials.

10.

What was the effect of moving the connecting wires so that the current travelled through a shorter length of the conductor? Explain.

Skill Practice

11.

(a) How precise were your measurements?

(b) What sources of error could have affected the accuracy of your results?


12.

Write a summary that answers the question: Do different materials have different values of electrical resistance? Use your data to support your answer.


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11.3


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1.

(a) How is current related to potential difference in a circuit?

(b) How is current related to resistance in a circuit?

2.

What does Ohm’s law state?

3.

Copy this table into your notebook, and complete the values for potential difference, current, and resistance in an electric circuit.


V I

0.5 V

20 A

R

50

⍀

100 ⍀

6.0 V 4.0 A


8.

What is the resistance in the circuit shown here?

Question 8

3.0 A

6.0 V

4.

What is each of these meters called?

(a)

(b)

5.

What does each meter in question 4 measure?

6.

Draw labelled circuit diagrams to show how each meter in question 4 is connected in a:

(a) series circuit

(b) parallel circuit

7.

(a) What is a fuse?

(b) What is a fuse used for?

(c) If a fuse melts, does it create an open circuit, a closed circuit, or a short circuit?

9.

A 12-

⍀ light bulb is in a series circuit powered by a 6.0-V battery.

(a) What is the current in the circuit?

(b) If you changed the 12-

⍀ bulb to a 24-

⍀ bulb, what current would be drawn from the battery?

10.

(a) If a 36-

⍀ bulb is added in series in the circuit in question 9(a), what is the current in the circuit?

(b) What is the potential difference across each bulb?

11.

In a circuit where voltage is kept constant, state what happens to current if resistance is:

(a) doubled

(b) quadrupled

12.

(a) Why is a ground fault circuit interrupter necessary for electrical devices that are used around water?

(b) List three devices that should include a ground fault circuit interrupter.

Reflection

13.

What questions about electricity would you like to have answered?



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Investigating

Home

C A R E E R S

Quit

in Science

Great CANADIANS in Science

Max Donelan

Award-winning Canadian scientist Dr. Max

Donelan walks down many different scientific paths. In fact, walking is something he would like to help more people be able to do. While most healthy people find walking a simple matter, many individuals who suffer from paralysis due to a stroke find that any kind of walking can be one step too far.

A stroke is a medical condition that occurs when a blood vessel in the brain leaks. This leakage of blood causes brain and nerve damage. For example, the damage can make it difficult to use the muscles on one side of the body while the other side is not affected at all. A person who has had a stroke may be able to walk but may find that he or she needs to use much more energy than a healthy person to do the same amount of walking.

Dr. Donelan is working to find out why.

Dr. Donelan and his colleagues at Simon Fraser

University in British Columbia are studying the science behind the way healthy people walk. They will use the results of their studies to design devices and strategies to help patients use energy efficiently and regain as much mobility as possible.

Even healthy people may benefit from his research. In studying the energy requirements involved with walking, Dr. Donelan’s team has come up with a device that is able to capture energy that is generated when a person walks

(Figure 11.47). His device assists the movement of leg muscles while generating electricity at the same time. This is called “harvesting” energy.

Harvesting usually refers to gathering in crops like grains or vegetables when they are ripe. In this case, the crop is energy!

Figure 11.47

Dr. Donelan watches his device in use. It is strapped to the knee of this walker. For every minute of walking you do, the device harvests enough electrical energy to power a cell phone for about 30 minutes.

Dr. Donelan’s team is working to design an energy harvester that is lightweight, slim, and barely noticeable when worn. Being able to produce your own electricity is useful to people in locations where a constant electrical power supply is not available, such as hikers and emergency crews. In the field of energy efficiency, Dr. Donelan is clearly a step ahead.

Questions

1.

What does it mean to “harvest” energy?

2.

ScienceSource Research to find out what possible applications a human-powered energy harvesting device could have in one of the following fields:

• medicine

• public safety

• the military


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Science in My FUTURE

Line Installers and Repairers

Are you ready for a career challenge? Suppose your job description included climbing a telephone pole at night during a snowstorm when the power was out — in fact, you would be climbing the pole because the power was out?

Electrical energy is an essential part of our society, and waiting for a storm to end is not usually an option when the power grid goes down.

Line installers and repairers are sent out often during a summer lightning storm or a winter freeze-up to keep electricity flowing to homes and businesses (Figure 11.48).

As a line installer, you would do more than make sure the lines were properly connected and repaired. Line installing and repair includes working with electronics and telecommunications, such as telephone, Internet, and cable television lines. New construction, which involves putting up poles or burying cables, means you are likely to use a variety of equipment, such as diggers, trench makers and tunnelling machines. Although machines would help you lift and carry, you would need to be strong and physically fit. Climbing to high places and working with high voltage carry a definite risk, so an attitude of being careful and working safely is essential. You might set up service in homes for customers, so good people skills are also an asset.

For a career as a line installer and repairer, high school completion that includes algebra and trigonometry is an asset, as are the kinds of practical skills learned in shop classes.

Community colleges and technical schools often offer programs in electricity, electronics, and telecommunications. These programs frequently partner with companies in the local community to offer hands-on field work.

Figure 11.48

A line installer needs a good understanding of electrical safety.

Even our increasingly wirelessly connected world, we will still need tough, smart, cautious, and strong individuals to keep the grid working properly.

Questions

1.

List four qualities that would be an asset for a person interested in work as a line installer or repairer.

2.

ScienceSource There are many careers related to electrical technologies, including electricians, power plant operators, and radio and telecommunications equipment installers and repairers. Select one of these or another related field, and summarize what the job involves, the education and training needed, and one aspect of the job that is particularly interesting to you.


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Thinking and investigation c


Application


3.0 A

4.0 V

V

1

9.0 V

A

1

Question 1

1.

(a) Is the circuit above a series circuit or a parallel circuit? k

(b) List all the parts of the circuit above. k

(c) What is the voltage at V

1 above? k in the circuit

(d) What is the current at A

1 above? k in the circuit

2.

Draw a circuit diagram of a circuit that includes a battery, an ammeter, and a light bulb with a voltmeter, all properly connected together. c

3.

How is a parallel circuit different from a series circuit?

k

4.

(a) What happens to all light bulbs in a series circuit when one burns out?

k

(b) How does the situation change when the lights are hooked up in parallel?

k

5.

Are circuits in a home connected in series, in parallel, or in combinations? Explain your answer, using examples of actual rooms in your home.

k

6.

What is the difference between an open circuit, a closed circuit, and a short circuit?

k

7.

Assume that each resistor in a circuit is of a different value. What type of circuit does each of the following statements describe: series or parallel?

k

(a) The voltage is the same across every resistor.

(b) The voltage varies across each resistor.

(c) The current varies through each resistor.

(d) The current remains constant throughout the whole circuit.

8.


⍀ resistor that is connected across a battery.

Find the voltage of the battery. a

9.

A 120-V outlet has an appliance that draws

10 A connected to it. What is the resistance of the appliance?

a

10.

Copy and convert each of the following units in your notebook: a

(a) 1.6 MV = ____ V

(b) 1500 W = ____ kW

(c) 650 mA = ____ A

11.

(a) What is the value of a resistor that transforms 2.0 mA of current when it is connected to a 6.0-V battery? a

(b) Reformulate question (a) twice. In the first question, make voltage the unknown. In the second question, make current the unknown.

a


12.

The word “circuit” means a complete path.

Draw and label a real-life, non-electric example of: c

(a) a series circuit

(b) a parallel circuit


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13.

Explain the reasons for each of these safety rules.

a

(a) Do not poke a knife into a plugged-in toaster to clear out bread crumbs.

(b) Avoid using an extension cord that is thinner than the cord you are attaching to it.

(c) When disconnecting an appliance, pull the plug, not the cord.

(d) Do not plug many electrical cords into one outlet.

(e) Do not use a kite, stick, pole, etc. close to an overhead wire.

(f) Make sure your hands are dry before touching any electrical device, cord, plug, or socket.

(g) Never use a frayed electrical cord.

14.

(a) What is dangerous about the situation shown in the picture below? a

(b) What should the worker do to be safer?

a

(c) The drill is plugged into the wall with a three-prong plug. How does the third prong on the plug act as a safety mechanism?

k

15.

What are two ways you could increase current in a circuit?

t

16.

Why does an electrical cord on a lamp not heat up when the light bulb filament does?

t

17.

You want to find the value of an unlabelled resistor. You have a voltmeter, an ammeter, wires, and a battery. How could you find the value of the resistor accurately?

t

Reflection

18.

(a) What do you think is the most useful information you learned in Chapter 11?

Why? c

(b) How might you put your understanding of this information to practical use? c

After Reading


With a partner, list all the ways that this chapter supports understanding of unfamiliar terms.

Revisit your personal list of terms and definitions.

Which terms are now more familiar to you? Which terms might you need to review? What strategies will best help you to review those terms? Create two study goals for this chapter based on your understanding of terms.

Question 14

Unit Task Link

In this chapter, you set up series and parallel electric circuits that could light one or more light bulbs. An electrical grid composed of several generating stations and a number of communities is a complex electrical circuit. However, many of the basic principles you have learned about simple circuits apply to it. Consider how series and parallel circuits might be used to supply electricity from two generating stations to three communities. Sketch a simple circuit that would connect all three communities to both generating stations so that each community has a reliable source of electricity.


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12

Home Quit



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Home

Wind turbines can share the land with crops or grazing animals. A number of wind turbines are often connected together in “wind farms” to produce electrical energy.

Quit



• determine the energy consumption and operating costs of various appliances

• calculate the efficiency of an energy converter



• assess social, economic, and environmental effects of producing electricity from renewable and non-renewable sources

• produce a plan of action to reduce electrical energy consumption at home and outline the responsibilities of various groups in this project


We are using up non-renewable resources more rapidly than ever before to generate electricity. Now is the time to change this cycle. Your knowledge of electricity can help you make intelligent choices and understand complicated debates about global energy issues.

Before Writing

Get Your Reader’s Attention

Good writers want you to be interested in what they have to say. They often use the opening sentence in a paragraph as a hook to get you reading further.

Survey the first paragraph under each main subheading in chapter 12, and decide which one best grabs your attention.

Key Terms

• efficiency • hydroelectricity • kilowatt-hours

• non-renewable resources • renewable resources

• sustainability • thermoelectric generating plant

• thermonuclear

We can reduce our electrical energy consumption and use renewable energy resources to produce electrical energy.

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12.1

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Renewable and Non-Renewable Energy

Resources for Generating Electricity


• Electrical generators transform the energy of motion into an electric current.

• Most electricity generated in

Canada is from hydroelectric or thermoelectric sources.

• Other energy sources include biomass, geothermal energy, sunlight, wind, and tides.

• There are both renewable and non-renewable energy sources.

• Every energy source has both pros and cons.

• We need to move toward sustainability in our use of resources.

Figure 12.1

Students in Elliot Lake helped install solar energy panels on their school for generating electricity.

N

Thunder

Bay

Elliot Lake

Sault Ste. Marie

0 50 100 km

Sudbury

Toronto

Ottawa

Windsor

Figure 12.2

Location of the town of

Elliot Lake

Local Solutions to Generating Electricity

When you turn on the light in your bedroom, you are using electricity that was generated far from your home. A large hydroelectric dam, a coal-burning generating plant, or a nuclear generating plant is probably the source of your electricity. In some areas of Ontario, the source is wind farms made up of giant wind turbines. To build a hydroelectric dam or enough wind turbines to generate electrical energy for a large number of people requires a huge investment in money, people, and equipment. Usually, governments and businesses build these large-scale projects.

Coal and oil are non-renewable resources . A non-renewable resource is one that cannot be replaced once it is used up. However, in the past 10 years, governments have invested small-scale projects that use other sources of energy, such as the Sun, to generate electrical energy. The Sun and the wind are renewable resources .

A renewable resource is one that can be reused or replaced.

In some parts of Ontario and elsewhere in Canada, renewable energy sources can be a practical alternative to non-renewable


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Elliot Lake Secondary School is one example of a small renewable energy project (Figure 12.1). Students at the school proposed to the government that they would place

12 solar panels and a wind turbine on the roof of their school. They pointed out that the electricity generated from these two energy sources would help provide electricity to the school. The project also supported the community of

Elliot Lake’s program to reduce its dependence on nonrenewable energy sources such as coal and oil (Figure

12.2). Impressed with the students’ ideas, the government of Ontario awarded them a $50 000 grant. Figure 12.1

shows students at the school installing solar panels at the school. Now the students also have work experience related to installing solar panels and wind turbines.

All over Ontario and Canada, communities are developing small-scale projects to produce electrical energy using renewable energy methods (Figure 12.3).

Figure 12.3

The GreenWorks Building at the

Kortright Conservation Centre in Toronto generates electricity using solar energy.

(© Toronto and Region Conservation, all rights reserved)

D25 Quick Lab

Renewable Energy Projects in Your Community

Renewable energy projects can be found all over

Ontario. Using print and electronic resources, you and your classmates will learn about examples of these projects in your community.

Purpose

To identify and describe the function of renewable energy projects in your community


• information summaries about renewable energy projects

Procedure

1.

Your teacher will provide summaries of projects using renewable resources for generating electrical energy in your area or elsewhere in the province.

2.

With a partner or small group, select one project to work on.

3.

Create a summary of the key features of the project

— type of technology used, reason for the project, costs, and value to users and the community.

4.

Present your findings to the class.

Questions

5.

How many different kinds of renewable methods for generating electricity did you discover?

6.

Are some methods of generating electricity more common than others? Why do you think this is the case?

7.

What do you think is one reason there are not more renewable energy projects in your community?


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Figure 12.4

Michael Faraday

(1791–1867)


A turbine converts steam or moving water to mechanical energy using paddles or fins or even buckets. The word “turbine” comes from the Latin turbo, meaning spinning top or whirlwind.

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Generating Electricity

In 1831, an English chemist and physicist named Michael

Faraday made an electrical discovery that changed the world

(Figure 12.4). Faraday introduced a way to generate a steady supply of large amounts of electricity. He demonstrated that an electric current can be generated by moving a conducting wire through a magnetic field, a process called electromagnetic induction.

We use electromagnetic induction today to generate electricity in large-scale generators (Figure 12.5). Most generators do the same job: they transform the energy of motion into an electric current. The magnets inside a generator are rotated by a turbine , which is a machine that uses the flow of a fluid to turn a shaft.

The magnets spin coils of copper wire. This pulls electrons away from their atoms and creates a current flowing in the copper wire.

The current is sent through transmission lines to reach cities and towns. The web of interconnections between generating stations, substations, and users is called an energy grid or a distribution grid (Figure 12.6). Generating electricity starts with a spinning turbine and ends up at your wall socket. But where does the energy come from to spin the turbine?

Figure 12.5

The electricity we use in our homes and schools is produced by massive coils of wire rotating between magnets in huge generators, like this one in

Nanticoke, Ontario.

Figure 12.6

An electric power grid transfers energy from the generating stations to the users. The whole grid is a complete circuit.

476 UNIT D The Characteristics of Electricity generating station substation transmission line underground power wires underground power wires transmission line

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Using Water Power to Generate Electricity

Most electricity generated in Canada is hydroelectricity , which means it is generated by harnessing the power of flowing water.

Some hydroelectric stations in smaller communities use fast-flowing rivers to turn their turbines. Other hydroelectric stations, such as the ones at Niagara Falls, use the flow from a waterfall to turn their turbines (Figure 12.7).

Most communities do not have a waterfall, so a dam may be built across a river to store water in a reservoir. The water is then directed through a channel called a penstock to a turbine with ridges around it (Figure 12.8). The water turns the turbine, which is connected to a generator.

During Writing

Show What You Know

As a writer, you want to convince a reader that you know your topic. Add details, use facts, and present evidence to demonstrate your knowledge.


The prefix “hydro-” comes from the

Greek word hudor, which means water.

transformer

Figure 12.7

The Sir Adam Beck

Generating Station at Niagara Falls generator water flow penstock turbine

Figure 12.8

In a hydroelectric generating station, water flows through a penstock. As it flows past the turbine, it causes the turbine to turn. The turning turbine is connected to the generator. The generator converts the energy from the turning motion of the turbine to electrical energy.


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The combining forms “therm-” and

“thermo-” are from the Greek word for heat.

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Using Heat to Generate Electricity

If there are no waterfalls or rivers in your area, what mechanical force can be used to turn the turbines? One answer is steam. In many areas, thermoelectric generating plants use a fuel such as coal or biomass to heat water to create high-pressure steam.

Fossil Fuels

Coal, oil, and natural gas are fossil fuels , which means they were produced from the organic matter of organisms that lived millions of years ago. A fossil fuel, usually coal, is burned in a generator to boil water. The steam is kept under great pressure in pipes, which allows it to reach higher temperatures than normal. The high-pressure steam strikes and pushes the blades on the turbine (Figure 12.9).

coal in combustion chamber cooling tower condenser water exhaust steam high-pressure steam turbine

Figure 12.9

A coal-fired generating station generator transformer

Figure 12.10

Corn husks are an example of biomass that is burned to boil water to make steam to turn a turbine.

Biomass

Biomass is organic material made up of plant and animal waste.

Examples of biomass include wood, peat, straw, nut shells, sewage, and corn husks (Figure 12.10). In a biomass system, the organic waste decomposes to produce a gas called methane. The methane gas can be burned to boil water to make steam. The most common biomass material used today is wood waste from lumber and from pulp and paper industries.


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Nuclear Energy

Ontario requires a huge amount of electrical energy. We have a large population and are a major centre of manufacturing. Our electrical energy needs far surpass what hydroelectric and thermoelectric generators supply. Fiftyone percent of our electricity in Ontario is thermonuclear , which means it is produced by heat in nuclear power stations (Figure 12.11).

In a nuclear reactor, atoms of a heavy element, usually uranium, are split in a

Figure 12.11

The Pickering Nuclear Power Plant is one of three nuclear generating stations in Ontario.

chain reaction. This splitting, called nuclear fission, releases an enormous amount of energy. The nuclear fission of just 1 kg of uranium is equivalent to burning about 50 000 kg of coal. The energy released by the fission process is used to heat water to produce steam to turn a turbine.

Geothermal Energy

In some places in the world, water is naturally heated by hot rock deep in Earth’s crust and rises to the surface as hot water and steam

(Figure 12.12). The energy from this hot water and steam is called geothermal energy . Geothermal energy sources at or near Earth’s surface are hot enough to heat homes and other buildings. For generating electricity, hotter sources are needed.

High-temperature geothermal sources are found deep in areas where there is volcanic activity. Iceland has active volcanoes and many hot springs. It uses geothermal energy to produce 19 percent of its electricity. In Canada, geothermal sources hot enough to be used to drive turbines for electricity generation are located in

British Columbia. Tests are under way there to determine how to use geothermal sources cost effectively.

Figure 12.12

A hot spring is an example of geothermal energy.


1.

What is a non-renewable resource?

2.

What does a generator do?

3.

What is a turbine?

4.

What source does most of Canada’s electricity come from?

5.

What is a fossil fuel?


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Figure 12.13

A solar cell has specially treated layers that create current when exposed to sunlight.

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Other Energy Sources

There are other energy sources that can be used to generate electricity. As different technologies continue to be developed and refined, our ability to use these sources economically increases.

Solar Energy

Many people think solar cells are a new technology, but the roots of this invention go back to 1839, when French scientist Edmond

Becquerel soaked two metal plates in an electricity-conducting solution. When Becquerel exposed one of the plates to sunlight, he could detect a small potential difference between the plates. He had invented the first solar cell. Scientists now make solar cells using silicon (Figure 12.13). sunlight

A

B

C

D

E

F

A Protective cover glass

B Antireflective coating to let light in and trap it

C Metal contact grid to collect electrons for circuit

D Silicon layer to release electrons

E Silicon layer to absorb electrons

F Metal contact grid to collect electrons from circuit

Solar modules (several cells connected together) and arrays

(several modules) have many uses, including powering calculators, lights in telephone booths, and the International

Space Station. A solar farm includes arrays of mirrors that focus sunlight onto a liquid that is heated and used to turn water into steam to drive the turbines (Figure 12.14). One of the world’s largest solar energy projects includes solar farms in Sarnia and

Sault Ste. Marie and aims to produce enough electricity for about

9000 homes.

Figure 12.14

The mirrors in this solar array focus heat from the Sun on a container that is part of a system to turn water into steam.


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Wind Energy

Wind turbines use the energy of moving air to spin their blades, which are connected to a generator (Figure 12.15). The amount of energy a wind turbine generates depends on how fast the wind is blowing, with approximately 10 km per hour being the minimum for power generation.

In Ontario, the wind blows strongly enough, on average, about

20 percent of the time, but in some areas of Canada and the world, winds are stronger and more consistent. Wind energy currently provides about 1 percent of Ontario’s electricity, but it is one of the fastest-growing energy sources in the world.

Tidal Energy

Tidal energy uses the energy of the gravitational pull of the

Moon. North America’s only tidal power generating station is in

Annapolis Royal, in Nova Scotia, where the powerful tides of the

Bay of Fundy spin its turbines (Figure 12.16). The station provides enough electricity for about 4500 homes.

Tests are under way in British Columbia and Nova Scotia for a promising new technology called a tidal stream generator, which works like an underwater windmill. Other marine energy sources that are being tested include ocean wave energy and ocean thermal energy.

Figure 12.15

A wind farm near

Shelburne, Ontario

Figure 12.16

This tidal power station in Nova Scotia generates electricity by using the energy of the water as it rises and falls in the daily cycle of tides.


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80

70

60

50

40

30

20

10

0

Relative Costs of Electricity Generation Technologies

(Canadian cents per kilowatt hour, 2003)

SOURCE: CERI, Relative Costs of Electricity Generation Technologies , September 2006

Figure 12.17

Relative costs of electricity generation technologies

Comparing Methods of

Generating Electricity

Energy sources for generating electricity can be grouped into two broad categories. Nonrenewable energy sources are sources that are limited and cannot be renewed naturally.

Fossil fuels (natural gas, propane, coal, and petroleum) are non-renewable sources, as is uranium. Once these materials are used up, they cannot be replaced.

Renewable energy sources are sources that can be replenished by natural processes in a relatively short time, such as sunlight, wind, tides, and waves. Biomass is a renewable source if the trees or other plants that produce it are properly managed.

A few of the advantages and disadvantages of using different energy sources are summarized in Table 12.1 and

Table 12.2. A comparison of the approximate costs of using each source is shown in

Figure 12.17.

Table 12.1

Some Advantages and Disadvantages of Non-Renewable Sources for Electricity Generation

Source Some Advantages Some Disadvantages

Fossil fuels – Fossil fuel generating stations can quickly adjust to changes in electricity demand.

– The technology for using these fuels is already in place.

– The burning of fossil fuels releases pollutants into the atmosphere and directly contributes to global warming.

– Mining coal is hazardous to workers and damages the environment.

Nuclear – Nuclear power is inexpensive to produce.

– Nuclear power produces enormous amounts of energy from very little fuel.

– Nuclear waste is poisonous and radioactive and needs to be stored very carefully for hundreds or thousands of years.

– Nuclear plants are very costly to construct and to maintain.


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Table 12.2

Some Advantages and Disadvantages of Using Renewable Sources for Electricity Generation

Source Some Advantages Some Disadvantages

Flowing water

(hydroelectricity)

– Large hydroelectric generating stations produce electricity inexpensively.

– Reservoirs may be used for flood control, irrigation, drinking water, and recreation.

– Small-scale hydroelectric plants using local rivers can be practical for some communities (Figure

12.18).

– There is a huge environmental impact when a dam is constructed, including flooding large areas of land, disruption or destruction of wildlife and fish habitat and migration routes, and displacement of

Aboriginal and other communities.

– Hydroelectric stations are very expensive to build.

Sunlight

Tides

Wind

– Solar cell energy is a convenient source of energy for small appliances, such as calculators.

– Solar energy is useful in remote areas.

– Once tidal generating stations are built, tidal energy is very inexpensive.

– Tides are more predictable than wind or sunlight.

– Wind energy production does not produce greenhouse gases that contribute to global warming.

– Farming and grazing can continue on land where wind turbines are located.

– Solar cell efficiency is low, so many photoelectric cells have to be used, which takes up large areas of land.

– Solar energy is the most expensive energy source at present.

– The environmental impact on marine life in area can be significant, due to changes in water level and water quality.

– Tidal energy is suitable for few areas as it requires very high tides.

– The wind does not always blow or remain constant.

– Wind turbines can present barriers to bird movement, cause bird fatalities due to collisions with turbine blades, and can disturb breeding, wintering, and staging sites.

Figure 12.18

Small-scale hydroelectric generating stations can be a local source of electrical energy.

Suggested STSE Activity •

D26 Decision-Making Analysis Case

Study on page 486


1.

What are three applications of solar cells?

2.

What does a wind turbine do?

3.

What is one of the fastest-growing energy sources in the world?

4.

How is electricity generated from tides?

5.

How is a renewable energy source different from a non-renewable energy source?


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Take It Further

Hydrogen may be our fuel of choice in the future. It can be burned like other fuels or converted into electricity in fuel cells. Find out how the most abundant element in the universe can be put to use for our electrical needs. Start your research at

ScienceSource .

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Electrical Energy Production in Canada

Canada is the world’s largest producer of hydroelectricity, the fifth-largest producer of electricity in general, and the second-largest exporter of electricity.

However, we need to be aware of the environmental implications of using non-renewable resources. As Figure 12.19

shows, a large part of our electricity is generated using non-renewable resources. These resources include coal, uranium

(for nuclear energy), oil, and gas. We must decide how to make a transition to using more renewable resources. We need electricity, but we also need to generate it wisely.

All of our energy sources are important to Canada because they provide us with flexibility and energy security and help us to become self-sufficient. For example, at one time, Prince Edward

Island was completely dependent on outside sources for electricity because it does not have fossil fuels, hydroelectricity, or nuclear power. However, the island now produces 18 percent of its electricity from wind energy and has become the first place in

North America to offer a guaranteed price to anyone — even a homeowner — who produces electricity from wind power.

In Ontario and across Canada, renewable energy projects for generating electricity are under way or being planned. However, as you can see in Figure 12.19, this type of electricity generation produced only 0.6 percent of our electricity in 2007. It cannot replace our use of non-renewable energy resources for now. To reduce our use of non-renewable resources, we have to find ways to use less electricity through technology and changing our usage habits.

Electricity Generated in Canada 2007

4.0

14.6

0.6

60.1

20.7

hydro coal nuclear oil and gas

Figure 12.19

Methods of electricity generation in Canada other


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A Sustainable Choice

Choosing the right methods for generating electricity means finding sustainable solutions. Sustainability means using resources at a rate that can be maintained indefinitely. If we do not achieve sustainable energy use, future generations in Ontario may not be able to support themselves.

A sustainable approach sometimes requires a different way of using resources. Sustainability may mean no longer using nonrenewable resources because they cannot be maintained indefinitely. In the past, fossil fuels were used up as quickly as possible to earn money and satisfy consumer demand. We need to use our resources in a way that makes them available over a longer period of time. With renewable energy methods, resources such as solar energy and wind are available indefinitely.

Figure 12.20 shows the main methods worldwide for generating electricity in 2007. Coal, oil, and gas account for

66.6 percent of electricity production. These three methods are using non-renewable resources. The other three methods, hydro, nuclear, and other account, for 33.4 percent of the production.

Hydro and other methods use renewable energy sources.

We may never be able to achieve complete sustainability, but the decisions we make personally and as a society can move us closer to this goal. An example of a personal decision would be to turn off the lights in your bedroom or classroom if you are the last person out of the room. This small action would save on electrical use. As you get older, you may make bigger decisions such as adding solar panels to a house you live in (Figure 12.21). Decisions such as these demonstrate you are keeping the goal of sustainability in mind.

Electricity Generated Worldwide in 2007

2.2

16.0

19.7


D27 Decision-Making Analysis on page 488

Figure 12.21

The people who live in this house are using solar panels to heat their water. This reduces their electricity use.

40.3

6.6

15.2

hydro coal nuclear oil gas other

Figure 12.20

How the world generates electricity. This graph could become very different during your lifetime.


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D26

CASE STUDY

STSE Decision-Making Analysis Skills Reference 4

Three Gorges: Potential Disaster or Good Choice?

Issue

The Three Gorges Dam on the Yangtze River in

China is the world’s largest hydroelectric generating station (Figure 12.22). The dam is 2.3 km long and

101 m high, with a reservoir that floods 632 km 2 of land. The dam provides electricity to nine provinces in China. Is the electricity the dam provides worth the problems it causes?

Background Information

Two students, Bassim and Kara, have been researching the Three Gorges Dam to find out the costs and benefits of this huge hydroelectric project.

The more they have learned about the dam, the more they are convinced of their own viewpoints.

Kara’s Viewpoint: In Favour of the Dam

The Three Gorges Dam is a good example of China’s commitment to using renewable resources to increase its production of electricity.

• Until recently, 82 percent of China’s electricity was generated in coal-burning stations. Three

Gorges could allow China to reduce coal consumption by 31 million tonnes per year,


■

■

Drawing conclusions

Justifying conclusions so millions of tonnes of greenhouse gases and pollutants will not be created.

• China plans to increase electricity from renewable resources from 7.2 percent to

15 percent by 2020. A series of smaller dams being built on the Yangtze will reduce silt and help to maximize the efficiency of the Three Gorges Dam.

• China is taking steps to minimize environmental damage. Billions of dollars already have been spent in water clean-up projects and in preventing landslides.

• The potential of the dam to prevent or reduce flooding for the millions of residents downstream means that far more lives and property can be saved than were lost due to the building of the dam.

• As well as providing flood control, the dam has improved navigation so that large ships can travel farther upriver, improving the economy of the area.

• The people of China need more electricity, and they have made a good choice in using renewable sources.

Figure 12.22

The Three Gorges Dam provides electricity to nine Chinese provinces. However, it has negatively affected millions of people who used to live where its reservoir now lies.


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D26 STSE Decision-Making Analysis (continued)

Bassim’s Viewpoint: Opposed to the Dam

The Three Gorges Dam is a social and environmental disaster and should not have been built. Millions of people live downstream from the dam and are in danger if the dam should ever fail.

• Over 1.2 million people were forced out of their homes so that their land could be flooded by the reservoir. Many of these people have had to move a second time due to an increase in landslides caused by filling the reservoir. Four million people are being encouraged to move before 2020.

• As well as submerging homes and more than

1300 archaeological sites, the reservoir also submerged factories, mines, and waste dumps. All the chemicals and other waste at those sites now contribute to the pollution of the reservoir. Also, only about 65 percent of the water flowing into the reservoir is treated, adding to the pollution and the possibility of diseases carried by water.

• The dam sits on a seismic fault, and there is danger of increased earthquakes and landslides.

Much of the silt that the river used to carry all the way down to the coast now settles in the reservoir and reduces the effectiveness of the dam. Cities such as Shanghai that are far downstream no longer have silt deposited to help build up their banks and may soon suffer from huge erosion problems.

Figure 12.24

The Yangtze River dolphin has become extinct since the construction of the dam.

• The changes in water flow affect downstream fish populations. These changes have resulted in the extinction of the Yangtze River dolphin and may be harming the populations of critically endangered

Siberian cranes (Figures 12.23 and 12.24).

Analyze and Evaluate

1.

Read both students’ viewpoints. Which student do you think presents a stronger case? Why?

2.

Choose one of the following roles. Prepare a presentation from that perspective, defending a possible course of action for an international energy conference.

• relocated villager

• wildlife expert

• government official

• industrialist

• Shanghai citizen

• geologist

• citizen of province receiving electricity from the dam

Skill Practice

3.

What is your conclusion about whether the electricity the dam provides is worth the problems it causes? Explain and justify your conclusion.

Figure 12.23

Siberian cranes are endangered birds that have been negatively affected by the dam’s construction.


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D27 Decision-Making Analysis Skills Reference 4

Producing Electricity in an Ontario Community


■ Gathering, organizing, and recording relevant information from research

■ Using appropriate formats to communicate results

Issue

Environmentally, it makes sense to close coalburning generating stations. Open-pit mining of coal scars the landscape. Burning coal releases pollutants into the air that cause acid rain. However, it does not make sense economically for now. The huge amount of power lost to the grid would have to be replaced.

The job losses would have a devastating effect on local economies. What recommendations would you make to a community that relies on burning coal for electricity generation?

Background Information

Every method of electricity generation has advantages and disadvantages. For example, the operation of wind farms along Lake Huron produces electricity from a renewable source (Figure 12.25).

This reduces dependence on non-renewable sources of electricity. However, the wind farms produce noise and visual pollution, affect local animal life, and reduce the amount of land available for agriculture.

Your goal is to identify some of the social, economic, and environmental implications of electricity production in a community in Ontario. You will research the social, economic, and environmental effects of one method of electricity generation that is different from the main method being used now in the community. You will also compare your proposed method to the present method. Then, you will make a presentation in support of your choice.

Analyze and Evaluate

1.

Meet with your group members to discuss the role each member will play in researching, formatting, and presenting your information.

Create a list of questions and key words that will help direct your research.

2.

Web 2.0

Work together to decide on a format for presenting your research. Develop your group’s research as a Wiki, a presentation, a video, or a podcast. For support, go to ScienceSource .

3.

ScienceSource Conduct your research online.

Copy and complete the chart below as part of your research.

Present

Method

Proposed

Method

Economic

- cost of producing electricity per kW•h

Environmental

- hazardous substances used or produced and their effects on surrounding ecosystem

Social

- effects of emissions on human health

4.

What percentage of the energy produced should come from your proposed method? Explain.

Skill Practice

5.

(a) What challenges did you have in researching the information you needed?

(b) How did you overcome the challenges?

Figure 12.25

Wind farms have to be placed where the wind is strong and steady enough to generate electricity cost effectively.


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12.1



1.

What is the function of a generator?

2.

What does “hydroelectricity” mean?

3.

What are four methods of generating electricity that use heat?

4.

Explain how a solar cell produces electricity.

5.

What are two different ways to make use of the tides to generate electricity?

6.

(a) What is the difference between renewable and non-renewable sources of energy?

(b) Create a chart that categorizes different energy sources as either renewable or non-renewable.

7.

(a) What is the source of most of the electricity generated in Ontario?

(b) What is the source of most of the electricity generated in Canada?

8.

The photos below show the type of solar cells that are installed on the “wings” of the

International Space Station. Why are solar cells used to generate electricity on spacecraft?

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9.

Compare the generation of electricity using coal with hydroelectric generation.

(a) How are the two methods similar?

(b) How are the two methods different?

10.

Why does an electrical generating station not use batteries to generate electricity?

11.

Suppose that residents of a remote community in northern Ontario decide to use wood as their primary energy source for heating the boiler of the community’s electrical generator. They cut down all the trees nearby and stockpile the wood, ready for use.

(a) What are the advantages and disadvantages of their solution for their energy needs?

(b) What recommendations would you make to ensure that this community has a reliable long-term energy supply?

Reflection

12.

(a) What information about electricity generation did you learn in this section that you did not know before?

(b) What are two questions that you have about electricity generation in Canada?


(a)

(b)

Question 8

The International Space Station (a) uses

2500 m 2 of solar cells (b) to generate its electricity.


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12.2

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Reducing Our Electrical Energy Consumption


• Electrical energy consumption is usually measured in kilowatthours (kW • h).

• Efficiency is the ratio of useful energy that comes out of a device to the total energy that went in.

• The EnerGuide label shows how much energy an appliance will use in a month of average use.

• Energy Star appliances are the most efficient appliances in their class.

• Energy conservation begins at home.

Figure 12.26

Consider how many times a day and how many different ways you use electricity.

The Cost of Electricity

Every method of generating electricity comes at a cost. There is an environmental cost, which affects the world you live in, and there is an economic cost, which gets passed on to you, the consumer. Each time you plug in an appliance, turn on a switch, or use electricity in any way, you are using precious resources and spending money (Figure 12.26). You can take steps to make better choices about how you use electricity. The first step is to understand where, when, and how you use electricity.

Most homes and apartment buildings have an electricity meter that tracks how much electricity is drawn from the energy grid. Older models of electricity meters have a turning disk with a black band

(Figure 12.27). The more electricity you have turned on in the house, the faster the disk turns. The energy used is calculated monthly or bi-monthly by reading a set of dials above the disk.

Figure 12.27

Older-style meters have to be read manually.


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Newer digital meters, called smart meters, are being installed across Ontario as part of a major energy conservation effort. The smart meters record electricity consumption hour by hour and send the information directly to the utility or electric company (Figure 12.28). Electricity costs are then calculated according to time of use, which includes time of day, weekdays versus weekends, and season.

The cost of electricity is higher during peak times, which are the busiest times of the day. You can save money on your electricity bill by moving activities that are energy-intensive to off-peak hours. You can help save resources by reducing your use of electricity at all times of the day.

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Figure 12.28

Smart meters use wireless and other technologies to send information directly to the utility.

D28 Quick Lab

Analyzing Home Electrical Use

Purpose

To categorize the use of electrical devices in your home

Procedure

1.

Create a list of all devices in your home that use electricity provided by the electric company or a home generator. Do not include anything powered by batteries, but do include battery chargers.

2.

Make a table using the rows shown on the right but without including the example devices. Add enough columns for all the electrical devices in your home. Give your table a title.

3.

Complete the table by estimating average usage and predicting the electricity requirements.

Questions

4.

Which device usages do you think you could reduce?

5.

What did this activity show you about your electricity usage that you did not realize before?

Clock radio

Number of devices 3

Time of day

Day(s) of week all all

Season all

Weekly usage (h) per device

Total weekly usage of devices (h)

Electricity requirements per use (low, medium, high)

168

504 low all

7

7 high

Dishwasher

1 all all


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Figure 12.29

A utility bill shows the amount of electricity used in kilowatt-hours.


The watt is named in honour of the

Scottish inventor and engineer James

Watt (1736–1819), whose improvements to the steam engine changed the world. The joule is named in honour of English physicist

James Prescott Joule (1818–1889), who studied the nature of heat and current through a resistor.

Electrical Energy Consumption

The electrical energy consumption for a household is the amount of electrical energy used, usually measured in kilowatt-hours. A kilowatt-hour (kW

• h) is equivalent to the use of one kilowatt in one hour. For example, if the energy ( E ) used by a microwave oven is

0.8 kW and the oven is turned on for half an hour, the electrical energy used is:

E = 0.8 kW × 0.5 h

= 0.4 kW

• h

One kilowatt (kW) equals 1000 watts (W).

A watt is equal to one joule per second. It does not take long for common electrical devices to consume a large number of joules. For this reason, the kilowatt-hour is often used as a unit for energy.

To calculate the cost of using an electrical device, you can multiply the energy consumed in kW

• h by the cost per kW

• h. In the microwave example above, the consumption of

0.4 kW

• h at a cost of 8 cents per kW

• h equals

3.2 cents. It may not sound like much, but remember that this was only one event over a half-hour time period. There is also an electricity delivery charge and taxes on top of the actual energy charge (Figure 12.29).


1.

Copy and complete this chart in your notebook. Give your chart a title.

Calculate the cost of using each appliance over the course of a year. Use a utility charge of 8.5 cents per kW • h.

Appliance

Average Use

(hours per day)

Vacuum cleaner

Hair dryer

0.1

0.25

Computer 4.0

Central air conditioning 12 (60 days/year)

Annual Energy

Consumption

(kW • h)

Annual Cost

($ per year)

38

100

520

1500


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Calculating Percent Efficiency

If you have ever accidentally touched a light bulb when it was lit, you know that it gets very hot (Figure 12.30). An incandescent light bulb uses only about 5 percent of its input energy to create light and converts over 95 percent of its input energy into heat. Compact fluorescent lights transform about 20 percent of their energy input into light, so they are more efficient than incandescent light bulbs.

5 J light energy

100 J electric energy

95 J heat

Figure 12.30

Most of the energy transformed by a light bulb is radiated as heat.

The efficiency of a device is the ratio of the useful energy that comes out of the device to the total energy that went in. The more input energy that a device converts into usable output energy, the more efficient the device is. Efficiency is usually calculated as a percentage.

E percent efficiency = × 100%

E in

During Writing

Organize for Impact

When persuasion is the goal, good writers like to create impact at the beginning and end of their piece of writing or presentation.

Watch television commercials, especially public service announcements, and note the methods for creating a powerful opener and a convincing closer for your presentation.





Suppose a light bulb uses 780 J of input energy to produce 31 J of light energy. What is its percent efficiency?

Given

Input energy = 780 J

Output energy = 31 J

Required

Percent efficiency = ?


Choose the correct equation.

Percent efficiency =

E out × 100%

E in

Substitute the values and their units. Solve the problem.

Percent efficiency = 31 J

× 100%

780 J

Paraphrase

% = 4.0%

The efficiency of the light bulb is 4.0 percent.


1.

A car produces 27.5 kJ of useful output energy from

125 kJ of fuel. What is the car’s percent efficiency?

2.

A fluorescent light produces 3.6 kJ of useful light energy from 21 kJ of input energy. What is its percent efficiency?

3.

A new high-efficiency brushless motor designed for electric-powered vehicles has an input energy of 75 kJ and an output energy of 72 kJ.

What is its percent efficiency?


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Comparing Efficiency

By comparing the efficiency of different devices, we can judge both their energy cost and their environmental impact. For example, a front-loading clothes washing machine uses much less electricity, washes more clothes per load, and uses less water than a top-loading washer. This reduces the energy needed to pump and heat water for laundry. Another example of improved efficiency is the refrigerator shown in Figure 12.31.

(a)

(b) thin fiberglass insulation thick polystyrene insulation low-efficiency compressor motor high-efficiency compressor motor

1970s mini-refrigerator Modern full-size refrigerator

Figure 12.31

The energy used to run a mini-refrigerator in the 1970s can run a full-size refrigerator today. In the last 25 years, refrigerator efficiency has increased 300 percent.

Read the Label

Sometimes, older equipment can be modified or adjusted to increase efficiency. But when it is time to buy a new appliance, there are labels that can help you make an informed choice.

All large appliances such as stoves, dishwashers, refrigerators, washers, and dryers have an EnerGuide label. This label states how much energy that appliance will use in a month or year of average use, as shown at

(a) in Figure 12.32. It allows you to compare the energy consumption of different brands and models. The arrow

(b) on the long shaded bar on the label below the rating shows the efficiency range of the appliance. If an appliance displays the Energy Star symbol (c), it is one of the most efficient appliances in its class.

(c)


Figure 12.32

You can use the EnerGuide label to compare appliances and determine which are more efficient. For example, you could compare refrigerators that have the same volume but are made by different manufacturers.

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How Off Is Off?

Suppose you finish using your computer and turn it off before leaving your room. As you walk by the living room, you notice the television has been left on even though no one is watching it, so you turn it off as well. These are good, energy-conserving actions, but have you really turned those appliances off?

If you look more closely, you may notice little lights still glowing on transformers and other devices (Figure 12.33). These machines are in a “standby” mode so that they will restart quickly when you switch them on. Many small appliances, such as computers, stereos, televisions, DVD players, and answering machines, still use electrical energy even when they are turned off.

Figure 12.33

If the standby light is on, electricity is being consumed.

Energy Conservation Begins at Home

You can make a plan to reduce the use of electricity in your home.

Asking questions is an excellent start. For example:

• Are lights being left on in rooms that are not being used?

• Is the clothes dryer being used for small loads like one shirt?

• Is the hot water running continuously while the dishes are being done?

• Is a lot of hot water being used for long showers?

• Are incandescent light bulbs being used instead of compact fluorescent bulbs?

If we lower our energy demands, we reduce the need to build more generating stations and we avoid greater impact on the environment and major construction costs. Your own personal action plan to reduce energy consumption will make a difference.

Reusing and recycling materials, conserving energy, and learning to live responsibly in harmony with our environment are key actions for living in a sustainable way.

Take It Further

Many people have contributed to our understanding of electricity.

Research one of the following names to find out when these people lived and what they contributed: Benjamin Franklin,

Luigi Galvani, Charles-Augustin de

Coulomb, Alessandro Volta, James

Watt, André-Marie Ampère, Georg

Ohm, Robert Millikan, Michael

Faraday, Thomas Edison, Nikola

Tesla, George Westinghouse. Begin your research at ScienceSource .


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A Self-Sufficient Energy Community

The 4300 people of Freiamt, a community in the southern part of Germany, decided that they wanted to own and control their own electricity generation. The community added rooftop solar systems to homes, barns, and garages and installed wind turbines. The community also has small-scale hydro and biomass generating stations. Some of the generators are jointly owned; others are privately owned.

The community’s electricity generation has been so successful that each year there is a surplus of about three million kilowatt hours of energy that is sold to Germany’s national energy grid.

1.

How could you adapt the community’s plan to make it suit your community?

2.

What do you think are the main points about

Freiamt’s plan that you could use to gain community support?

D30 Quick Lab

Electricity in Your Home

Purpose

To discover the pattern of electrical energy consumption in your home


• 1 year’s worth of electrical bills for your home or sample bills supplied by your teacher

Procedure

1.

Before starting, predict what months are the peak periods of electrical energy consumption in your home.

2.

Create a table with the following column headings. Give your table a title.

Actual Electricity Usage (kW

• h)

Adjusted Usage (kW

• h)

Cost of Electricity ($)

Delivery Charge ($)

Other Charges ($)

Total Charges

3.

For each bill, break down the different costs and add them to your chart.

4.

Total the charges.

Questions

5.

(a) What does the category “Other Charges ($)” include?

(b) What does “Adjusted Usage (kW

• h)” mean?

6.

(a) During which time periods is your household using electricity the most?

(b) Why might this be?

(c) How does this time period compare with your prediction from step 1?

7.

How would you change the bill to make it easier to understand?

8.

Write a summary paragraph explaining the pattern of electricity usage in your household.


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D31 Quick Lab

Marketing Compact Fluorescent Light Bulbs

As part of an effort to reduce energy use, the province of Ontario has banned the sale of inefficient incandescent bulbs, beginning in 2012.

Purpose

To create an effective marketing tool for compact fluorescent light bulbs

Procedure

1.

You and your partner have been hired by a public relations firm to help with the marketing campaign for compact fluorescent light bulbs

(Figure 12.34).

2.

Decide on the format you will use as part of the marketing campaign. You might design a brochure, make a poster, create a Web page, prepare computer slides, perform a rap song, create a skit, or choose another format as approved by your teacher.

3.

Read the following summary of points about both incandescent and compact fluorescent light bulbs. Consider both the pros and the cons in deciding how to reach your audience.

4.

ScienceSource Conduct research so you can make a strong case in favour of compact fluorescent light bulbs. You may want to research Ontario Power Generation, the Ontario

Ministry of the Environment, Natural Resources

Canada, and environmental groups such as the

Pembina Institute or the Sierra Club.

5.

Outline the roles and responsibilities of various groups, such as government, businesses, and family members, in making a success of the marketing campaign.

6.

Look in print materials such as magazines, newspapers, and books for information on the real costs of using various lighting options.

7.

Prepare and refine your presentation. You may wish to present your information to friends or family members and ask for their feedback.

8.

Share your presentation with the class.

Questions

9.

On the basis of your research, what do you think is the most important advantage of compact fluorescent bulbs?

10.

On the basis of your research, what do you think is the greatest disadvantage of compact fluorescent light bulbs?

Bulb

Compact fluorescent

Pros

- produces about four times more light than incandescent using the same amount of energy

Incandescent - less expensive to make than fluorescent

Cons

- much more expensive to make than incandescent

- contains mercury

- does not last as long as fluorescent

- is much less efficient than compact fluorescent bulbs

Figure 12.34

Compact fluorescent bulbs (left) are replacing incandescent bulbs (right) because they use less energy.


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1.

What does a smart meter measure?

2.

(a) What is electrical energy consumption a measure of?

(b) What units are usually used to measure electrical energy consumption?

(c) How is electrical energy consumption calculated?

3.

(a) How many watts are in a kilowatt?

(b) What does one thousand joules equal?

4.

(a) A microwave oven that draws 0.8 kW

• h is used for one hour. At a cost of

7.5 cents per kW

• h, what is the cost of the microwave’s electrical energy consumption?

(b) What is the cost for the microwave if it is used one day for 20 min?

(c) What is the cost of using the microwave for 20 min a day for a month of 30 days?

5.

What is the term for the ratio of useful energy that comes out of a device to the total energy that went in?

6.

What is the formula for calculating percent efficiency?

7.

What is the percent efficiency of a light source that uses 12.8 kJ of energy and delivers 4.3 kJ of useful light energy?

8.

What information is included on an

EnerGuide label?

9.

Suppose the standby light on your printer is on even though you have turned the printer off. What does the standby light indicate?

10.

What does an Energy Star symbol on an appliance indicate?

Question 10


11.

Describe how a smart meter is an improvement over older types of electricity meters.

12.

The costs for electricity are higher during peak times. Why do you think this is so?

13.

Why are incandescent bulbs regarded as inefficient?

14.

Create an EnerGuide label for an appliance with an Energy Star rating. You can use hypothetical values and names of companies.

15.

Why should you compare the efficiencies of appliances before making a purchase?

16.

How can we reduce the need to build more generating stations?

Reflection

17.

(a) How has the information in this section helped to make you a better consumer?

(b) How could you use this information to help you decide which electronic device to purchase?



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C O O L I D E A S f r o m J AY I N G R A M

A Light Show in Your Mouth

Jay Ingram is an experienced science journalist, author of The

Daily Planet Book of Cool Ideas , and host of the Daily Planet on

Discovery Channel Canada.

Have you ever experienced a chemical light show in your mouth? You might have if you have chewed a wintergreen candy.

You can observe the effect if you get some wintergreen candies and a pair of pliers, and sit in a very dark place, like the inside of a closet. Wait about five minutes until your eyes adjust to the darkness, and then crush one of the candies with the pliers (Figure 12.35). You will see an amazing flash of blue-green light!

The flash of blue-green light was first described in 17th century

Italy. However, the mechanism at work was not understood until several hundred years later.

The candy is made of sugar crystals, which are mostly empty space, with the atoms in them rigidly attached to each other. When you bite into the candy, the positive and negative charges in the crystals are separated, and this separation generates an electric potential difference.

When enough charge has accumulated, the negatively charged electrons jump across the gaps in the crystals to reunite with the positively charged protons.

As the electrons move, some of them collide with the nitrogen atoms in the air.

The nitrogen atoms absorb the tremendous energy of the collisions, and then emit blue-green light as they release their energy.

All sugar candy emits some light when you crush it. If there is only sugar, the blue light is harder to see, because much of the energy is released as ultraviolet light, which is not visible to humans. That is where the wintergreen comes in. Oil of wintergreen is very good at absorbing ultraviolet light and emitting it as visible blue-green light.

Question

1.

Write a summary of this feature. Include a main idea and one relevant point that supports it.

Figure 12.35 A wintergreen candy crushed by pliers in the dark.


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Thinking and investigation c


Application


1.

(a) List two non-renewable sources of energy.

k

(b) Name an advantage and a disadvantage of using each source.

k

2.

(a) List four renewable sources of energy.

k

(b) Name an advantage and a disadvantage of using each source.

k

3.

Describe what happens in nuclear fission. k

4.

What is sustainability? k

5.

(a) How do you convert watts to kilowatts?

k

(b) How do you convert kilojoules to joules?

k

(c) How many joules are in a watt?

k

6.

Suppose you bake a potato in a toaster oven that uses 1.2 kW. The oven is turned on for

25 min. How many kilowatt hours did it use?

a

7.

(a) If a motor uses 22 000 J while converting it to 13 400 J of useful energy, what is its percent efficiency?

a

(b) If a diesel truck produces 47.5 kJ of useful output energy from 125 kJ of diesel fuel, what is its percent efficiency? a

8.

Give two reasons for reducing energy waste.

k

9.

How can choosing to use a more efficient appliance benefit the environment? k

10.

Answer the following questions by referring to the EnerGuide label shown below. k

Question 10

(a) What is the energy usage of the rated appliance?

(b) Among similar appliances, which is rated most efficient?

(c) Is the rated appliance efficient? How do you know?

(d) List models similar to the one that is being rated.

11.

What does it mean if an appliance has an

Energy Star rating?

k


12.

Explain why you agree or disagree with the following statement: “A nuclear power plant provides energy using a radioactive source, so a turbine is not needed.” t

500

UNIT D

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13.

A group of Ontario farmers form a cooperative group and build a factory that turns corn into a fuel for generators and cars. Would this energy source be renewable or non-renewable? Explain. t

14.

Make a labelled pie chart or circle graph showing how electricity is used in your home. c

15.

Is it always a good idea to discard lowefficiency devices? Explain your answer. t

16.

(a) If you have a house in the country with a large property, what might you do to help reduce your dependence on the energy grid? t

(b) If you live in a mid-size house in the suburbs, what could you do to reduce your utility bill? t

(c) If you live in a small apartment in the centre of a city, what could you do to reduce your utility bill? t

17.

Choose an electrical device that you use daily. Identify changes you would make to the design of the device to maximize energy savings. Explain the reasons for your choices. Use a labelled diagram as part of your answer. c

18.

(a) Create a cartoon that shows at least seven ways that a home loses energy needlessly. c

(b) For each example shown, list a way to reduce that energy loss.

t

19.

What are seven practical ways to reduce electrical energy consumption in your school?

t

20.

Write a paragraph about the photograph shown at the top of the next column.

Include your personal response to the photograph, and explain what the photograph shows about electricity generation. c

Question 20

Reflection

21.

How could you improve the results of your work in the problem-solving and inquiry activities you did in this unit? c

After Writing


With your partner, meet with another pair who made a marketing presentation for fluorescent light bulbs. Provide positive feedback and helpful suggestions about the others’ presentation. How did it hook the audience? Which details, facts, or evidence were most effective in demonstrating knowledge? What were the points that created the greatest impact?

Unit Task Link

In this chapter, you have studied different methods of generating electricity and their social, economic, and environmental effects. Your knowledge of electricity can help you work within your community to decide on the best methods of power generation for your region. Think about the sources of energy for your community and whether they are reliable and sustainable. Suggest one form of energy production not being used now that might be an appropriate method for your community. Explain your choice.


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U N I T

D

Summary

Home

KEY CONCEPTS CHAPTER SUMMARY

10

Static charges accumulate on surfaces and remain there until given a path to escape.

• Static electric charges

• Law of attraction and law of repulsion

• Conductors and insulators

• Charging by friction

• Charging by contact and induction

• Using and reducing static charges

• Objects that gain electrons become negatively charged. Objects that lose electrons become positively charged. (10.1)

• Objects with like charges repel each other. Objects with unlike charges attract each other. (10.1)

• When an object is charged by contact, it takes the same charge as the charging object. (10.2)

• When an object is charged by induction, it takes the opposite charge to the charging object. (10.2)

• Charged objects attract neutral objects through the process of induction. (10.2)

• The principles of electrostatics are used in applications such as photocopying, spray painting, and filtering air. (10.3)

11


• Current electricity

• Electrical circuits

• Potential difference

• Electric current

• Direct current

• Alternating current

• Resistance

• Series circuits and parallel circuits

• Ohm’s law ( V = IR)

• Electrical safety

• Electrical circuits provide a complete path for electrons to flow. (11.1)

• Current electricity is the flow of electrons through a conductor in a circuit. (11.1)

• Potential difference or voltage ( V ) is the difference in electric potential energy between two points in a circuit. (11.1)

• Electric current ( I ) is a measure of the amount of electric charge that passes by a point in an electric circuit each second. (11.1)

• In direct current, electrons flow in one direction. In alternating current, electrons flow back and forth at regular intervals called cycles. (11.1)

• Resistance ( R ) is the degree to which a substance opposes the flow of electric current through it. (11.1)

• Series circuits provide one path for electrons to flow. Parallel circuits provide more than one path for electrons to flow. (11.2)

• Ohm’s law states that as long as temperature stays the same, V = IR. (11.3)

12

We can reduce our electrical energy consumption and use renewable energy resources.

• Generating electricity

• Renewable and non-renewable sources of energy

• Advantages and disadvantages of

• energy sources

E out

Percent efficiency = × 100%

E in

• Non-renewable sources used for generating electricity include fossil fuels and nuclear energy. (12.1)

• Renewable sources used for generating electricity include water, sunlight, wind, tides, and geothermal energy. (12.1)

• There are both costs and benefits from producing electricity from renewable and non-renewable sources. (12.2)

• Electrical savings can be achieved through the design of technological devices and practices in the home. (12.2)


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VOCABULARY KEY VISUALS

• charging by contact

(p. 407)

• conduction (p. 400)

• conductivity (p. 400)

• conductor (p. 400)

• coulomb (C) (p. 399)

• electric charge

(p. 394)

• electrical discharge

(p. 411)

• electron (p. 396)

• electron affinity

(p. 39 8 )

• electroscope (p. 404)

• electrostatics (p. 404)

• friction (p. 399)

• grounding (p. 40 8 )

• induction (p. 407)

• insulator (p. 400)

• law of attraction

(p. 399)

• law of repulsion

(p. 399)

• lightning rod (p. 41 8 )

• neutron (p. 396)

• nucleus (p. 396)

• proton (p. 396)

• static charge (p. 396)

• static electricity

(p. 396)

Lightning strike

• alternating current

(AC) (p. 439)

• ammeter (p. 439)

• ampere (A) (p. 439)

• battery (p. 435)

• circuit breaker (p. 463)

• circuit diagram (p. 450)

• current electricity

(p. 434)

• direct current (DC)

(p. 439)

• dry cell (p. 435)

• electrical circuit

(p. 434)

• electrical load (p. 434)

• electric current ( l )

(p. 439)

• electrochemical cell,

(p. 435)

• electrode (p. 435)

• electrolyte (p. 435)

• fuel cell (p. 4 8 6)

• fuse (p. 463)

• ground fault circuit interrupter (p. 464)

• ohm ( Ω ) (p. 441)

• ohmmeter (p. 441)

• Ohm’s law (p. 463)

• parallel circuit (p. 451)

• potential difference

(p. 437)

• potential energy

(p. 437)

• resistance ( R) (p. 441)

• resistor (p. 441)

• series circuit (p. 451)

• short circuit (p. 462)

• switch (p. 434)

• transistor (p. 449)

• volt (V) (p. 43 8 )

• voltage ( V ) (p. 437)

• voltmeter (p. 43 8 )

• wet cell (p. 435)

Microcircuits

• biomass (p. 47 8 )

• efficiency (p. 493)

• EnerGuide (p. 494)

• energy grid (p. 476)

• Energy Star (p. 494)

• fossil fuels (p. 47 8 )

• generators (p. 476)

• geothermal energy,

(p. 479)

• hydroelectricity

(p. 477)

• kilowatt-hour (kW•h)

(p. 492)

• non-renewable energy sources (p. 474)

• renewable energy sources (p. 474)

• thermoelectric generating plant

(p. 47 8 )

• thermonuclear (p. 470)

• turbine (p. 476)

Solar panels on rooftop

UNIT D Summary 503

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U N I T

D

Task

Bringing Electrical Energy to a Community

Quit

Solar cells can be used to generate electricity for individual buildings.

Getting Started

You are an electrical energy consultant working on a plan to add additional electrical energy generating sources in an area prone to blackouts. Suppose your electricity has a main supply source, such as a coal power plant or a nuclear power plant. However, a number of environmental factors have led to frequent blackouts. These factors include high winds and icing problems with transmission lines.

Your job includes developing new, smaller electricity generation sources. Each of these sources can connect to the regional electrical grid when the main source goes off-line or when main transmission lines to the grid fail.

These new, smaller-scale sources will help provide a consistent supply of electrical energy to the region, even if the main electrical supply becomes unavailable.

Your Goal

Your group will be in charge of planning a backup electrical generating station by researching existing examples of generating stations or technologies that can be used to generate electricity. Low-cost and environmentally friendly technologies are preferred. As a class, you will be required to propose a wide variety of technologies.

Criteria for Success

• Your plans for generating electricity must be environmentally responsible. For example, a plan to build a new dam across a river will need to consider the effect of creating a new lake, as well as the effect on migrating species of fish.

• Your plans for power generation must align with the other groups so that two groups are not competing to use the same natural resource, such as having two dams very close together.

• The types of generating methods your groups research must not all be the same. For example, if all groups plan a solar power generating station, this will be of little use if a blackout occurred at night.

• Your plans must be supported by references to existing examples of electrical generation sources. You will need to research your example enough to know what will be necessary to adapt it to your particular location. For example, if an oil-fired generating source is needed, will you be able to use a technology that captures and stores carbon dioxide emissions?

• Each group will submit a plan in order to create a class report that solves the problem of using backup generators to maintain consistent production of energy to the electrical grid.

Wind turbines can be used individually for small-scale electricity generation. They can also be grouped in wind farms for larger-scale generation.


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What You Need to Know

A century ago, energy was generated in the same location that it was used or only a few kilometres away.

Over the past 100 years, extensive electrical grids have been developed that are powered mainly by large generating stations. In many cases, smaller generating stations were discouraged or even prohibited from adding energy to the electrical grid.

This is beginning to change as many smaller, more efficient, and often more environmentally friendly ways of generating power are being encouraged.

For this task, you need to research one or more of these newer technologies for generating electricity by finding existing examples of where they are being used.

You will then determine ways to adapt them to your local region.

What You Need

• a large map of your region showing population centres, useful geographical features, and main lines of the power grid

• Internet access for researching examples of methods of electrical power generation

Procedure

1.

As a class, decide on the number of new generating stations that can be planned. Do this by dividing the size of the class by the size of each planning group.

2.

As a class, brainstorm the specific geographical features that may be of use for electrical power generation in your community. This may involve using only real features in your area, or you may agree to include features not actually present but which will be useful for the purpose of this activity.

Examples of features could include a fast-flowing river or waterfall, a high ridge that is usually windy, a large water supply useful for construction of cooling towers, or geothermal energy. You may wish to estimate the average annual hours of sunshine to determine whether to include solar energy.

3.

Form groups, and within your group brainstorm ideas for electrical generation methods. Agree on several options to bring back to the class for discussion.

4.

As a class, share the ideas of each group.

Remember that methods of electrical generation must be varied and must not conflict with each other or represent a threat to the environment.

Agree as a class on what type of power generating source each group will investigate and where on the regional map each generating station will be located.

5.

ScienceSource Research a plan for your generating station by examining existing stations or technologies already.

6.

Design your generating station. Use clearly labelled diagrams.

7.

Present your plan for the generating station.

Describe how it fits into the overall regional plan with all of the groups’ plans.

Assessing Your Work

8.

(a) Think about your role in the work your group accomplished. What do you think was the strongest contribution you made to your group’s work?

(b) How could you improve your contribution to group work in future activities?

9.

(a) What do you feel was the most effective aspect of your group’s plan?

(b) How could your group’s design have been improved?

10.

Write an evaluation of your approach to solving this problem. Did it work well? What would you have done differently and why?

UNIT D Task 505

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ACHIEVEMENT CHART CATEGORIES t

Thinking and investigation a

Application k

Knowledge and understanding c

Communication

Home

7.

Suppose you know that balloon A below is negatively charged but you do not know the charge on balloon B.

Key Terms Review

1.

Create a mind map using the following terms. You may add more terms if you wish.

c

• ammeter

• ampere

• battery

• current

• fuse

• kilowatt-hour

• load

• ohm

• potential difference

• resistance

• switch

• voltmeter

• volt

10

Static charges accumulate on surfaces and remain there until given a path to escape.

2.

(a) Suppose you walk across the carpet, touch a metal doorknob, and get a shock.

What charge do the particles causing the charge have: negative or positive? t

(b) Use the structure of the atom to explain why these particles have the charge you identified in part (a). k

3.

(a) State the law of attraction.

k

(b) State the law of repulsion.

k

4.

Explain the steps you would take to tell the difference between a positively charged object and a negatively charged object. k

5.

Use a series of diagrams to explain how a charged object attracts a neutral object.

c

6.

Suppose two different materials are rubbed together. Each one is brought near a charged electroscope with no effect on the electroscope. Explain what may be the reason that there is no effect.

k

+

–

–

–

–

+

–

?

A B

Question 7

(a) When you bring the two balloons together, they repel each other. What is the charge on balloon B?

k

(b) Suppose that when you bring the two balloons together they attract each other. Does this observation prove that balloon B is positive? Explain why or why not. k

8.

Object C is rubbed on object D. The leaves of a negatively charged electroscope temporarily move closer together when object D is brought near.

(a) What charge does object D have?

k

(b) What charge does object C have?

k

9.

Use a Venn diagram to compare and contrast charging by contact and charging by induction.

k

10.

Use labelled diagrams to explain how lightning occurs.

c

11.

(a) When clothes come out of a clothes dryer, they sometimes stick to each other. Explain why.

k

(b) Name three different ways to reduce this effect.

k

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12.

Explain the function of the metal rods in the photograph below.

k

Question 12

13.

How have static electricity controls helped in developing new technologies?

k

14.

(a) Name one device that would function better if static electricity were eliminated.

k

(b) Name one device that would not function as well if static electricity were eliminated.

k

11


15.

(a) What are the two main components of an electrochemical cell? k

(b) What is the function of each component? k

16.

Copy and complete the following chart in your notebook. k


Quantity Definition Abbreviation Unit Symbol

Potential difference

Current

Resistance

17.

(a) What are four factors affecting resistance in a wire? k

(b) Describe how each factor affects resistance. k

18.

Why does a light bulb light up immediately after you turn on a switch, even if the switch is a long way from the bulb?

k

19.

(a) Draw a circuit diagram that includes a battery, connecting wires, and a resistor.

a

(b) Add a voltmeter to the circuit diagram to measure the potential difference across the resistor. a

(c) Add an ammeter to the circuit diagram to measure current through the resistor.

a

20.

(a) Use circuit symbols to draw a series circuit with a battery, connecting wires, and two light bulbs.

a

(b) Draw a parallel circuit using the same components as (a). a

(c) Describe the difference in current flowing in the two circuits (a) and (b).

a

(d) What will happen to the brightness of the bulbs in circuit (a) if one of the bulbs is unscrewed?

a

(e) What will happen to the brightness of the bulbs in circuit (b) if one of the light bulbs is unscrewed?

a

21.

(a) What is the voltage at V

1 below? a in the circuit

(b) What is the current at A


(c) Is this circuit a series circuit or a parallel circuit? k

2.0 A

V

1

9.0 V

3.0 V

Question 21

A

1

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22.

(a) What is the voltage at V

1 below? a in the circuit 29.

How is steam used in the generation of electricity?

k

(b) What is the current at A


(c) Is this circuit a series circuit or a parallel circuit?

k

30.

What are three different electricity generating systems you could use on your property to provide electrical energy if you lived on a small farm? k

3.0 A

V

1

2.0 A A

1

3.0 V

Question 22

23.

Draw a circuit that keeps two lights on at all times and can switch two other light bulbs on and off independently. a

24.

What does Ohm’s law state?

k

25.

If the resistance of a load becomes larger, does current also become larger? Explain your answer.

k

26.

Most homes in Ontario are built to meet regulations that ensure safety and dependability of electrical systems. What are some ways in which the electrical system in your home has been made as safe as possible?

k

27.

Why is it a good idea to use fused safety power bars for televisions, computers, and other sensitive electrical equipment?

k

12


28.

(a) Describe the difference between renewable and non-renewable energy sources.

k

(b) Give two examples of each type of source.

k

31.

What effects do the following electricity generation methods have on surrounding ecosystems?

(a) wind farms k

(b) hydroelectric dams k

32.

What types of hazardous substances are used or created in the production of nuclear power?

k

33.

State some disadvantages of:

(a) solar power k

(b) tidal power k

34.

What is the price difference between electricity produced from solar power and by coal-burning plants?

k

35.

In what units is electrical energy consumption usually measured?

k

36.

The efficiency of a device is a ratio. What is it a ratio of?

k

37.

What information does an EnerGuide label provide? k

38.

What does an Energy Star label indicate?

k

39.

How could you use the EnerGuide and

Energy Star labels to help you decide when purchasing appliances or electronics?

k

40.

What causes the difference in energy consumption between a conventional and a front-loading washing machine?

k


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41.

List five appliances found in the home that consume electrical energy even when they are not in use?

k

42.

What are three benefits of lowering our energy demands?

k


43.

(a) When lightning hits a car, is it safer to be in the car or outside the car but touching it? Explain why. a

(b) You are standing close to a tall tree when you suddenly see lightning and hear thunder. Should you take shelter under the tree, run across the field to the nearest building, or do something else?

Explain why.

a

44.

How are a lightning bolt and a spark similar? t

45.

You have just combed your hair, and you bring the comb near some bits of paper. The paper is attracted to the comb, but as soon as the paper touches the comb, it is immediately deflected away. Explain what is happening in terms of charge motion, charging methods, and the triboelectric series.

t

46.

Some machines have a grounding screw connected to a wire or cable as shown in this photograph.

(a) Explain what grounding a charged object does.

k

Question 46

(b) Explain why some objects need to be grounded.

k

(c) Give two examples of machines or devices that need to be grounded. t

47.

How does the charge on a charged electroscope compare with the charge in a functioning circuit?

t

48.

Explain why a cow that touches an electric fence gets a mild shock. A bird sitting on the same wire does not receive a shock.

Why? a

49.

The voltmeter and the ammeter are electrical loads. Each has an internal resistance. Relative to the resistors in the circuit, would their internal resistances be large or small? Explain. t

50.

Why do lights dim in the house when certain appliances, such as an oven, hair dryer, or table saw, are used? t

51.

For the following situations, explain the safety concern. a

(a) A worker carries a large aluminum ladder near overhead hydro lines.

(b) Someone takes the third prong out of a plug in order to use it with a two-prong extension cord.

(c) The washing machine electrical cord is frayed.

(d) You run out of fuses and put a piece of aluminum in place of the fuse.

52.

A friend replaces a cord on a kettle with a new cord that is much thinner than the original. When the kettle is plugged in, the new cord gets much hotter than the old one did. Explain why. t

53.

Could a thermal generating plant be effective without a turbine? Explain. t

54.

(a) What is meant by a “non-thermal” method of generating electricity? t

(b) Describe an example of such a method. t


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55.

Suppose a more efficient appliance costs more than a regular appliance. Does it make sense to spend the extra money? Explain. t

61.

The graph below shows the relationship between voltage and current that emerged in tests for a particular resistor. Does this resistor work according to Ohm’s law?

Explain. t

56.

Create a sketch, paragraph, or skit using electrical terms in a humorous manner. You should get a “charge” from doing this

“potentially” fun exercise at “ohm” or at school. c

Current vs. Voltage

Skills Practice

57.

What is the value of a resistor that transforms 2.0 mA of current when it is connected to a 6.0-V battery? a

58.

(a) What voltage is applied to a 5.0Ω resistor if the current is 1.5 A? a

(b) A voltage of 80 V is applied across a

20-

Ω resistor. What is the current through the resistor? a

(c) The current running through a starter motor in a car is 240 A. If this motor is connected to a 12-V battery, what is the resistance of the motor? a

59.

Copy and complete the following chart in your notebook.

Use Ohm’s law to create a set of data given that there are three resistors in series and each one has a resistance of

40

Ω

. a

Voltage and Current

Voltage

(V)

Current

(A)

2.0

4.0

6.0

8 .0

10.0

60.

Copy and convert each of the following units in your notebook. a

(a) 1.6 MV = ____ V

(b) 1500

Ω

= ____ k

Ω

(c) 650 mA = ____ A c u rre n t v o lt ag e

Question 61

62.

Copy and complete the following chart in your notebook. a

Percent Efficiency

Device Input

Energy (kJ)

Gaspowered

SUV

675

Gas-electric hybrid car

675

Output

Energy (kJ)

8 1

195

Percent

Efficiency

Natural gas furnace

110 000

Electric baseboard heater

Alkaline dry cell

9.5

8 4.52

8 5 000

6.0

74.3

8


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Revisit the Big Ideas and Fundamental

Concepts

63.

Create a poster on your opinion of one of the following topics.

c

(a) Why we should use renewable sources to generate electricity

(b) Why we should conserve energy

64.

Nuclear energy is one of the most efficient ways to produce electrical energy. Why are not all power plants nuclear? a

65.

Choose a renewable source for generating electricity. Explain possible solutions to its disadvantages. t

66.

Create a timeline that begins with this year and extends 30 years into the future. On the timeline, detail the steps your community could take to become energy self-sufficient.

Include: c

• the new technologies for generating electricity that could be installed, including where you recommend installing them

• the energy-conserving methods that could be implemented

67.

Write a three-paragraph essay in answer to the following question: “How can we improve our lives by controlling, using, and conserving electricity in an environmentally friendly way?” c

STSE

Science, Technology, Society, and the Environment

68.

Create a graphic representation, such as a mind map or other chart, to answer the following questions. Include labelled diagrams if you wish.

c

(a) What are the costs and benefits associated with the production of electrical energy from renewable and non-renewable sources?

(b) How can electrical efficiencies and savings be achieved through the design of technological devices and practices in the home?

69.

Based on the activities you have done in this unit, answer the following questions.

Include your personal observations. You may wish to include labelled diagrams and/or refer to specific activities as part of your answer.

c

(a) What are the properties of static electricity and current electricity?

(b) What is the relationship between potential difference, current, and resistance in an electrical circuit?

Reflection

70.

(a) After completing this unit, how have you changed your attitude toward how you use electrical energy?

c

(b) What changes are you thinking of implementing?

c
