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Current electricity is the continuous flow
of electrons in a closed circuit.
The Characteristics of Electricity
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Skills You Will Use
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.
In this chapter, you will:
• 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
Concepts You Will Learn
In this chapter, you will:
• 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
Why It Is Important
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
Here is a summary of what you
will learn in this section:
• 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.
Electric Fish, Eels, and Rays
Figure 11.2 The electric eel uses
electricity to defend itself and to stun
its prey.
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UNIT D
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.
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.
Purpose
To discover how to make flashlight bulbs light up
using a standard battery
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.
Materials & Equipment
• 1 D dry cell
• 5 insulated copper wires with both ends bare
5. Explain how to use wire and a dry cell to make
two bulbs light up. Include a labelled sketch in
your answer.
• two 2.0 V-flashlight bulbs
CAUTION: Disconnect the wires if they get hot. Do not
use dry cells if they show any sign of corrosion.
Current electricity is the continuous flow of electrons in a closed circuit.
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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.
W O R D S M AT T E R
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.
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
is called an electrical c i rc u i t. The continuous flow of electrons in
a circuit is called c u r re n t e l e c t r i c i t y.
Electric Circuits
A circuit includes an energy source, a conductor, and a load. An
electrical l o a d is a device that converts electrical energy to
another form of energy. For example, in Figure 11.4, the light bulb
is the load. It converts electrical energy to light and heat.
Many electric circuits also include a switch. A s w i t c h is a
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.
energy source
+
electrical load
conducting wires
switch
Figure 11.4 An electric circuit
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The Characteristics of Electricity
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Electrochemical Cells
One simple and convenient energy source is a battery. A b a t t e r y
is a combination of electrochemical cells. Each e l e c t ro c h e m i c a l
c e l l 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
D
B
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.
C
A
E
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.
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
Current electricity is the continuous flow of electrons in a closed circuit.
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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.
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
Figure 11.7 During recycling, the chemicals in a dry cell are
separated and can be reused.
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.
Learning Checkpoint
1. How is current electricity different from static electricity?
2. What is an electric circuit?
Figure 11.8 A fuel cell converts
chemical energy into electrical
energy. This fuel cell is slightly
smaller than this textbook.
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UNIT D
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.
W O R D S M AT T E R
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.
Current electricity is the continuous flow of electrons in a closed circuit.
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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).
How Electrons Transfer Energy in a Circuit
Figure 11.11 The orange device is a
voltmeter. It is showing a reading of
1.50 V. The yellow device is a
battery.
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.
Learning Checkpoint
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
W O R D S M AT T E R
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.
Current electricity is the continuous flow of electrons in a closed circuit.
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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).
(c)
–
(d)
(b)
+
(a)
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.
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.
W O R D S M AT T E R
Figure 11.17 When electrons pass through a resistor, such as the element on this electric
The symbol for ohm, ⍀, is the Greek
letter omega.
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
Figure 11.18 The filament in a
light bulb is an example of a
resistor.
Current electricity is the continuous flow of electrons in a closed circuit.
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Resistors and Potential Difference
high potential energy
potential energy converted
to another form of energy
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.
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.
Learning Checkpoint
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
Suggested Activities •
D13 Quick Lab on page 444
D14 Quick Lab on page 445
D15 Design a Lab on page 446
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The Characteristics of Electricity
Abbreviation
Unit
Symbol
Potential difference
ampere
⍀
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Resistance in a Wire
Take It Further
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.
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
How Factor Affects Resistance
Material
Silver has the least resistance but is very expensive to use
in wires. Most conducting wires are made from copper.
Temperature
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.
Current electricity is the continuous flow of electrons in a closed circuit.
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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
Materials & Equipment
• 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?
(b)
(a)
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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UNIT D
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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
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.
Materials & Equipment
• 50-cm or longer length
of rubber tubing
• 1000-mL beaker or
bucket
• water tap and sink or
bucket
• stopwatch
10. Follow your teacher’s instructions for cleaning
up.
Procedure
Questions
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.
Time to Exit Empty
Tube (s)
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.
Time to Exit
Pinched Tube (s)
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 Fill Beaker
or Bucket with
Pinched Tube (s)
Time to Fill Beaker
or Bucket with
Open Tube (s)
Time to Fill Beaker
or Bucket with
Water on Full (s)
Current electricity is the continuous flow of electrons in a closed circuit.
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D15 Design a Lab
Skills Reference 2
Investigating Conductivity
Question
How does the conductivity of different solutions
compare?
Materials & Equipment
• 100-mL graduated
cylinder
• 250-mL beaker
• distilled water
• conductivity tester
• tap water
• vinegar
• copper(II)
sulphate solution
• other solutions
provided by your
teacher
• salt water
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.
Analyzing and Interpreting
Figure 11.23 Conductivity tester
9. Rank the substances in order of high
conductivity to low conductivity.
Procedure
Part 1
10. How did your results compare with your predictions?
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.
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8. How did you determine whether there were
differences in conductivity between the solutions
you tested?
The Characteristics of Electricity
Skill Practice
11. Make an hypothesis about why there were
differences in conductivity between the
solutions.
Forming Conclusions
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 CHECK and REFLECT
13. Make a list of similarities between the flow
of water and an electric circuit.
Key Concept Review
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?
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
(b) What are the units for measuring
potential difference?
(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?
4. (a) What device measures current?
(b) What are the units for measuring
current?
5. What is the difference between potential
difference and current?
zinc can
(negative
electrode)
insulated
casing
insulator
positive
terminal
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?
electrolyte
paste
negative
terminal
carbon
electrode
insulator
Question 15
Reflection
Connect Your Understanding
11. Why must a circuit be closed in order for a
current to flow?
16. What do you now understand about current
electricity that you did not know before
reading this chapter?
12. Use a three-circle Venn diagram to compare
and contrast alternating current, direct
current, and static electricity.
For more questions, go to ScienceSource.
Current electricity is the continuous flow of electrons in a closed circuit.
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Series Circuits and Parallel Circuits
Here is a summary of what you
will learn in this section:
• 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
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?
Materials & Equipment
• 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.
(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.
Current electricity is the continuous flow of electrons in a closed circuit.
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Circuit Diagrams
load
switch
conducting wire
electrical source
Figure 11.26 The four basic parts of
a circuit
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
it. A drawing made with these symbols is called a c i rc ui t d i agra 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
Function
wire
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
measures current through a device, connected
in series
voltmeter
measures voltage across a device, connected in
parallel
Learning Checkpoint
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
A s e r i e s c i rc u i t is an electric circuit in which the components
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
A p a ra l l e l c i rc u i t is an electric circuit in which the parts are
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.
Current electricity is the continuous flow of electrons in a closed circuit.
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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.
The current is the same throughout
a series circuit.
The current decreases
when more resistors are
added.
Parallel circuit
Each load uses all the potential
difference supplied by the battery.
The current divides into different
paths. A pathway with less
resistance will have a greater
current.
Adding resistors in parallel
decreases the total
resistance of the circuit.
Two Types of Circuits
Suggested Activities •
D17 Quick Lab on page 453
D19 Inquiry Activity on page 455
D20 Inquiry Activity on page 456
Figure 11.30 A combination circuit.
The switch in this circuit can turn all
the bulbs on or off.
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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Learning Checkpoint
Take It Further
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?
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.
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?
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
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.
Materials & Equipment
Questions
• 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.
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.
Current electricity is the continuous flow of electrons in a closed circuit.
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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. Clean up your work area.
Figure 11.32 A voltmeter connected across a resistor
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D19 Inquiry Activity
Skills Reference 2
Series Circuit Analysis
Question
3. Record the voltage across each resistor and the
power supply.
What are the properties of a series circuit?
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.
Materials & Equipment
• 6.0-V battery
• multimeter (or
voltmeter and
ammeter)
• three 100-⍀ resistors
• switch
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.
• connecting wires
CAUTION: Open the circuit if the wires and resistors
get hot.
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
Planning for safe practices in
investigations
Gathering, organizing, and
recording relevent data
from inquiries
Resistor
2
Resistor
3
Part 1:
Current
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.
Analyzing and Interpreting
9. State what you noticed in Part 1 about the:
Voltage
(a) current across the resistors in all cases
Part 2:
Current
(b) sum of all voltages across the resistors
10. State what happened in Part 2 to:
Voltage
(a) the current
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
(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.
6.0 V
V
resistor 1
(b) the voltages across each resistor
resistor 2
resistor 3
Figure 11.33 Construct this circuit in step 2.
Forming Conclusions
13. In a paragraph, summarize the properties of a
series circuit.
Current electricity is the continuous flow of electrons in a closed circuit.
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D20 Inquiry Activity
Skills Reference 2
Parallel Circuit Analysis
Question
3. Record the voltage across each resistor and the
power supply.
What are the properties of a parallel circuit?
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.
Materials & Equipment
• multimeter (or
voltmeter and
ammeter)
• 6.0-V dry cell
• three 100-⍀ resistors
• connecting wires
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.
• switch
CAUTION: Open the circuit if the wires and resistors
get hot.
Procedure
Part 1 — Potential Difference and
Current Measurements
Resistor
1
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.
1. Create a data table similar to the one below. Give
your table a title.
Power
Supply
Selecting instruments and
materials
Observing, and recording
observations
Resistor
3
Part 1:
Current
8. Measure and record the voltage across the power
supply and across each of the two resistors.
Analyzing and Interpreting
9. State what you noticed in Part 1 about the:
(a) current across the resistors in all cases
Voltage
(b) sum of all voltages across the resistors
Part 2:
Current
10. State what happened in Part 2 to:
(a) the 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.
(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
resistor 3
V
resistor 2
6.0 V
resistor 1
A
12. Did the voltages across any resistors equal the
total voltage provided by the source? Explain why
they did or did not.
Forming Conclusions
Figure 11.34 Construct this circuit in step 2.
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13. In a paragraph, summarize the properties of a
parallel circuit.
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11.2 CHECK and REFLECT
4. (a) Draw a circuit diagram that shows three
resistors in series.
Key Concept Review
1. Copy and complete the following chart in
your notebook.
Voltage and Current in Circuits
In a Series
Circuit
In a Parallel
Circuit
Voltage
2. (a) Draw a circuit diagram of the circuit
shown here.
Connect Your Understanding
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.
(b)
(c)
–
(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.
Current
+
(a) Will the order in which you hook up the
light bulbs in series affect the intensity
of light each emits? Explain.
(a)
(d)
(b) Draw a circuit diagram that shows three
resistors in parallel.
(b) What happens when you hook up the
bulbs in parallel?
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?
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
(a)
(b) potential difference, current, and
resistance in a parallel circuit
2.0 V
4.0 V
6.0 V
Reflection
(b)
12 V
12 V
12 V
8. What images or memory aids help you
remember the differences between series
and parallel circuits?
For more questions, go to ScienceSource.
Current electricity is the continuous flow of electrons in a closed circuit.
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Ohm’s Law
Here is a summary of what you
will learn in this section:
• 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.
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.
A Fascination with Electricity
Figure 11.36 Georg Ohm (1789–1854)
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UNIT D
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.
W O R D S M AT T E R
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
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.
Materials & Equipment
5. Measure and record the current through the
resistor.
• 1.5 V dry cell
• resistors, any values from 15 ⍀ to 50 ⍀
• connecting wires
6. Record the resistance of the resistor you used.
• switch
7. Repeat steps 2 to 6.
• multimeter or voltmeter and ammeter
Trial
1.
Resistance
(⍀)
Current
(A)
Potential
Difference
(V)
8. Clean up your work area.
Resistance
ⴛ Current
Question
9. Multiply the resistance by the current for each of
the trials you completed. What can you infer from
your answers?
2.
Current electricity is the continuous flow of electrons in a closed circuit.
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Potential Difference, Current, and Resistance
I
V V
R
V = IR
Figure 11.37 Ohm’s law states that
potential difference (V) equals
current (I) times resistance (R).
Suggested Activities •
D23 Inquiry Activity on page 465
D24 Inquiry Activity on page 466
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?
460
UNIT D
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
Symbol
Unknown
Quantity
Symbol
Unit
Equation
Current,
resistance
IR
potential
difference
V
V
V = IR
Potential
difference,
resistance
VR
current
I
A
I=V
R
Potential
difference,
current
VI
resistance
R
⍀
R=V
I
Example Problem 11.1
A current of 4.0 A flows through a 40-⍀ 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.
The Characteristics of Electricity
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Example Problem 11.2
Practice Problems
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 = ?
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?
Analysis and Solution
The correct equation is I = V .
R
Substitute the values and their units, and then solve the
problem.
I=V
R
3. What would the current
be in question 2 if you
changed to a 45-⍀ bulb?
= 30 V = 2 A
15 ⍀
Paraphrase
A current of 2 A is generated.
Example Problem 11.3
Practice Problems
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
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?
Required
Resistance R = ?
Analysis and Solution
V
The correct equation is R = .
I
Substitute the values and their units, and then solve the
problem.
R=V
I
= 240 V = 12 ⍀
20 A
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?
Paraphrase
The resistance of the heating element is 12 ⍀.
Current electricity is the continuous flow of electrons in a closed circuit.
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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.
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 Circuits
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.
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.
Current electricity is the continuous flow of electrons in a closed circuit.
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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
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.
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.
D22
Figure 11.44 Ground fault circuit
interrupters are part of some electric
sockets.
STSE Science, Technology, Society, and the Environment
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.
464
UNIT D
The Characteristics of Electricity
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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SKILLS YOU WILL USE
D23 Inquiry Activity
Skills References 2, 10
Interpreting data/information to
identify patterns or relationships
Drawing conclusions
Investigating Ohm’s Law
Question
How are potential difference, current, and resistance
related?
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.
Materials & Equipment
• four 1.5-V dry cells
• switch
• connecting wires
• 2 different resistors
between 100 ⍀ and
300 ⍀
• voltmeter, ammeter
CAUTION: Disconnect the circuit if the wires or resistors
get hot.
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
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.
Resistor
(⍀)
1.5 V
3.0 V
4.5 V
6.0 V
Voltage
(V)
Current
(A)
Calculated
Resistance
Analyzing and Interpreting
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?
1. 100
2. 200
1. 100
11. Compare your data for all resistor 2 trials. When
voltage is increased across the resistor, what
happens to the current?
2. 200
1. 100
2. 200
Skill Practice
1. 100
12. What would happen to the current values if you
used a resistor with double the value of resistor 2?
2. 200
2. Construct the following circuit using resistor 1
and one 1.5 V dry cell (Figure 11.45).
Forming Conclusions
13. Describe the relationship between potential
difference, current, and resistance.
A
V
Figure 11.45 Construct this
circuit in step 5.
Current electricity is the continuous flow of electrons in a closed circuit.
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DI Key Activity
SKILLS YOU WILL USE
D24 Inquiry Activity
Skills Reference 2
Justifying conclusions
Identifying sources of error
Resisting the Flow
Question
Do different materials have different values of
electrical resistance?
Materials & Equipment
• connecting wires
• 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.
6. Repeat steps 4 and 5 for the copper wire,
Nichrome™ wire, rubber tubing, and the other
materials.
7. Clean up your work area.
Analyzing and Interpreting
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.
V
to calculate the
I
resistance for each current recorded in your table.
8. Use Ohm’s law R =
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
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.
11. (a) How precise were your measurements?
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.
Forming Conclusions
5. Move the clips on the graphite so that they are
1.0 cm apart. Record any change in the reading.
466
Figure 11.46 Determining resistance
UNIT D
The Characteristics of Electricity
(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 CHECK and REFLECT
Key Concept Review
Connect Your Understanding
1. (a) How is current related to potential
difference in a circuit?
8. What is the resistance in the circuit shown
here?
(b) How is current related to resistance in a
circuit?
3.0 A
2. What does Ohm’s law state?
6.0 V
3. Copy this table into your notebook, and
complete the values for potential difference,
current, and resistance in an electric circuit.
Question 8
Potential Difference, Current, and Resistance
V
I
50 ⍀
0.5 V
20 A
6.0 V
9. A 12-⍀ light bulb is in a series circuit
powered by a 6.0-V battery.
R
(a) What is the current in the circuit?
100 ⍀
(b) If you changed the 12-⍀ bulb to a 24-⍀
bulb, what current would be drawn
from the battery?
4.0 A
4. What is each of these meters called?
10. (a) If a 36-⍀ bulb is added in series in the
circuit in question 9(a), what is the
current in the circuit?
(a)
(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:
(b)
(a) doubled
(b) quadrupled
12. (a) Why is a ground fault circuit interrupter
necessary for electrical devices that are
used around water?
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) List three devices that should include a
ground fault circuit interrupter.
Reflection
(b) parallel circuit
13. What questions about electricity would you
like to have answered?
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?
For more questions, go to ScienceSource.
Current electricity is the continuous flow of electrons in a closed circuit.
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CAREERS
in Science
Great CANADIANS in Science
Max Donelan
Investigating
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!
468
UNIT D
The Characteristics of Electricity
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.
Current electricity is the continuous flow of electrons in a closed circuit.
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11 CHAPTER REVIEW
ACHIEVEMENT CHART CATEGORIES
t Thinking and investigation
k Knowledge and understanding
c Communication
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 Application
Key Concept Review
(a) The voltage is the same across every
resistor.
3.0 A
(b) The voltage varies across each resistor.
4.0 V
(c) The current varies through each resistor.
(d) The current remains constant
throughout the whole circuit.
V1
9.0 V
A1
8. A current of 1.5 A flows through a 30-⍀
resistor that is connected across a battery.
Find the voltage of the battery. a
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.
9. A 120-V outlet has an appliance that draws
10 A connected to it. What is the resistance
of the appliance? a
k
(c) What is the voltage at V1 in the circuit
above? k
(d) What is the current at A1 in the circuit
above? k
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
(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
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
Connect Your Understanding
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
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UNIT D
The Characteristics of Electricity
(a) 1.6 MV = ____ V
(b) 1500 W = ____ kW
3. How is a parallel circuit different from a
series circuit? k
6. What is the difference between an open
circuit, a closed circuit, and a short circuit?
10. Copy and convert each of the following
units in your notebook: a
12. The word “circuit” means a complete path.
Draw and label a real-life, non-electric
example of: c
(a) a series circuit
k
(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.
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?
(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.
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
(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.
(b) How might you put your understanding
of this information to practical use? c
(g) Never use a frayed electrical cord.
After Reading
14. (a) What is dangerous about the situation
shown in the picture below? a
(b) What should the worker do to be safer?
Reflect and Evaluate
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
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.
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.
Question 14
Current electricity is the continuous flow of electrons in a closed circuit.
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