Grade 9 Science
Unit 3: Electricity
Important Concepts and Key Terms Guideline
Concept
Chapter 7: Static Charge
Electricity is an integral
part of our lives
Description/Notes
Students complete a paired brainstorming activity looking at how
they use electricity in their daily lives
(Balloon Science Activities to show static electric charges)
Static Electricity
The buildup of charge on an object; Static means “to stay”. So
charges stay with the object
Current Electricity
The flow of electric charge; no longer staying in one place
Neutral
No charge. The positive and negative charges are equal
Positive Charge
There are more positive charges (protons) than negative charges
(electrons)
Negative Charge
There are more negative charges (electrons) than positive charges
(protons)
How are objects charged?
All solid materials are charged by the transfer of electrons.
Positive protons vibrate in the nucleus but cannot escape because
they are bigger! Negative electrons are smaller and float around
the nucleus and are free to be transferred to other objects if they
are close or in contact with one another!
How do charges on objects
change?
If an electron is removed from a neutral atom, a negative charge
has been taken away and the object is positively charged!
If an electron is added to a neutral atom, a negative charge has
been added, making the object negatively charged!
When the number of protons = number of electrons, the object is
neutral!
Positively charged atoms need to gain electrons to become neutral.
Negatively charged electrons need to lose electrons to become
neutral!
-Use students as nucleus, protons, electrons to show how the
charges transfer
-Do activity on page 231: Visualizing Charge Transfer
Electric Discharge
The removal of electric charge from an object. Lighting: Page
244: “Visualizing Lightning”
Laws of Electric Charges
Like charges repel.
Unlike charges attract
Charges objects attract neutral objects
Static electricity and the
development of
Technology
Lightning Rod: A metal rod or conductor attached to a building
and electrically connected to the ground. If lightning hits the
building, it will preferably hit the rod and the electricity will be
conducted into the ground instead of through the building
Photocopiers: A photocopier uses a static electricity image to
attract ink. The toner (ink) becomes negatively charged and the
paper is positively charged so they attract! Page 241 of text book
looks at the steps involved in making a photocopy!
Electrostatic precipitator (air cleaner): removes particles from air
using electrostatic charges. They work like a filter, attracting dust
and smoke particles in the air thus, cleaning the air!
Other examples: fabric softener, bounce sheets, electric eels!
Static vs Current Electricity
Although static electricity is built up and does not move around, it
cannot be harnessed as a useful energy source. It cannot be used
or collected to run electrical devices. Current electricity can
because it can flow from one point to another
Careers in Electricity
There are many jobs associated with the production and
maintenance of technologies using electricity. Students can
brainstorm and create mind maps of these careers – particularly
mention the photocopier technician and an electrician
Chapter 8:Ohm’s Law
Introduction Video (10
minutes)
http://www.youtube.com/watch?v=F1p3fgbDnkY&feature=related
Excellent video for showing: Potential energy, electric potential
difference, coulomb, electric circuit, cell, battery and volt!
Page 261 of student text book: Figure 8.9 – Swimmer going down
slide shows the same idea as the video!
Potential Energy
Stored energy in an object
Electric Potential Energy
The electrical energy stored in a battery; electrons have stored
energy and the ability to do work after they leave the battery
Coulomb
Symbol is C. It is a unit of electrical charge. 1 C = the addition or
removal of 6.25 x 1018 electrons or the number of electrons that
pass through a 100W light bulb in 1 second!
Electric Potential
Difference
Also known as “voltage”. The amount of electric potential energy
(stored energy) per on coulomb of charge
Page 252 in Text: Comparing Potential Energy and Potential
Difference
Look at Figure 8.4 to describe potential energy
Volt
The SI unit for measuring electric potential difference – symbol is
V (Named after Alessandro Volta, Italian physicist who invented
the battery)
Electrochemical cell
Converts chemical energy into electrical energy stored in charges
so that we are able to use the energy. Commonly just called a cell.
Battery
A collection of electrochemical cells. Dry cells are batteries used
in flashlights and portable DVD players. Wet cells are used in cars
and motorcycles.
Electrode
The 2 terminals on a battery (positive and negative sides).
Usually, made of 2 different metals but can also be made of a
metal and another type of material. The electrodes sit in an
electrolyte.
Electrolyte
A substance that conducts electricity. In a dry cell it is a moist
paste; in a wet cell, it is a fluid.
How does an
electrochemical cell
produce electric charge?
Page 253 of student textbook
Figure 8.6 shows an electrochemical cell with electrodes and
electrolytes. Read “Producing Voltage” and discuss the zinc and
copper electrode example.
Electric current
The flow of charged particles in an electric circuit
Ampere
The SI unit for electric current. Symbol = A. It is defined as 1
coulomb of charge passing a given point per second. Named after
French physicist Andre-Marie Ampere who looked at the
relationship between electricity and magnetism.
Electric circuit
A complete pathway that allows electrons to flow. Remember
drawing circuit diagrams… Also, remember the introduction
video!
Page 261 of Student Text: Figure 8.8
Parts of an electric circuit
1. Source of electrical energy – electrochemical cell or battery
2. Conductor – the wire through which energy flows
3. Electrical load – a device that changes electrical energy into
other forms of energy. Examples would be light bulbs, motors,
heaters
4. Controls/Switches – A device that turns the circuit on or off
Conductor
Allows electricity to flow through. In a circuit, the conductor is
the wire through which electricity flows
Circuit Diagrams
Diagrams that use symbols to represent the different components
of the circuit
Resistor
A resistor controls or limits the amount of current passing through
a circuit
Resistors are marked with colored bands. These stripes indicate
the resistance of the resistor.
Page 277: Figure 8.22 shows the bands (students do not need to
know the colors or their values, just that they indicate resistance)
Ammeter
An ammeter is a device used to measure the amount of current
passing through a circuit
Voltmeter
A voltmeter is a device that measures the amount of voltage (or
electric potential difference) that is in a circuit
Open switch
In a circuit, an open switch shows that there is a break in the path
of the electrons and the electrons cannot continue to flow. An
open switch exists when you turn OFF lights… you open the
switch and electrons can no longer get to the light bulb to give the
bulb energy!
Closed switch
In a circuit, a closed switch shows that there are NO breaks in the
path of electrons. They are able to continue to flow. A closed
switch exists when you turn ON lights… there is a continuous
flow of electrons from the switch to the light bulb, allowing the
light bulb to turn on.
Create Circuit Diagrams
using appropriate symbols
Hand out: “Circuit Diagram Symbols”
Page 263: Drawing Circuit Diagrams
Electrical resistance
Measured in Ohm and describes how a material can slow down the
flow of electrons and convert electrical energy into other types of
energy. It is the ratio of voltage to current.
Ohm
The SI unit for electrical resistance. The symbol is Omega -
Georg Ohm
Defined the relationship between voltage, current and resistance
and is why electrical resistance is measured in Ohm
Factors that affect
Resistance in a Wire
1. Length – longer = more resistance
2. Diameter – Smaller = more resistance
3. Type – Some wires offer more resistance than others. Copper is
an excellent wire for electricity because it offers very little
resistance and electrons can flow easily. Nichrome is a
combination of nickel and chromium and is a strong resistor!
4. Temperature – higher temperatures result in more resistance
because all of the electrons are erratic
Ohm’s Law
Ohm’s Law states that:
Resistance (R) = Voltage (V) or
Current (I)
R=V
I
Resistance will be measured in Ohm ( )
Voltage will be measured in Volts (V)
Current will be measured in Amperes (A)
Rearranging Formula
Show the Triangle using 3 Variables so they can rearrange the
formula to find R, V or I when given the other 2 variables.
Calculate V, I or R when
given 2 of the variables
Refer to page 273 in the Student Textbook. Complete the
provided example on the board with students.
Practice problems: Page 273 # 1,2,3
Chapter 9: Circuit
Control
CORE Lab must be
completed in this chapter
Series circuit
Resistors and Ohm’s Law
Lab 8-3D
Only one path for current to travel. The current is the same in
each part of a series circuit. Each load in a series circuit uses a
portion of the same source voltage.
Parallel circuit
There is more than 1 path for current to travel. The voltage across
each resistor in a parallel circuit is the same. Current entering a
parallel circuit must divide among the possible paths.
Excellent Chart!!
Page 294 of Student Text: Table 9.1: Series and Parallel
Circuits. Students can review this chart for answers to the
next 6 sections of these notes!
Describe current and
voltage at different places
throughout a series circuit
The current in each part of the series is equal because it travels in
one path only. When you add a resistor, you increase the total
resistance but you decrease the total current throughout the circuit.
Each load of a series circuit will lose a portion of the total voltage
supplied to the electrons by a battery. The sum of the voltages lost
will equal the total voltage supplied by the batter. The losses do
not have to be equal amounts.
See page 289 for diagrams of current and voltage in series.
How do resistors affect
series circuits?
When you add a resistor in a series circuit with other resistors, the
total resistance of the circuit increases! However, you then
decrease the total current throughout the circuit.
Describe current and
voltage at different places
throughout a parallel circuit
Loads that are parallel will have the same voltage.
Loads of different resistance in parallel will have different
currents. However, the sum of the currents in each parallel path
must equal the total amount of current given by the battery.
See page 292 for diagrams of current and voltage in parallel.
Describe how a resistor
affects parallel circuits.
When you connect resistors in parallel, the total resistance
decreases because there is now more than 1 path that the current
can follow. However, now the total current leaving the battery
must increase.
How are series circuits
affected by removing load?
If more than 1 load (light bulbs, say) are connected in series, then
if one light bulb is removed, the other light bulbs will go out. This
is because removing a light bulb now leaves the circuit open and
electrons cannot continue their path through the system.
Many Christmas light sets are connected in series. When one bulb
blows, the others do not work!
How are parallel circuits
affected by removing load?
If loads (bulbs) are connected in parallel, when one light goes out,
the others continue to function. This is because the electrons have
more than 1 path around the circuit.
Household lights are connected in parallel. If a light bulb blows in
your kitchen, your lights remain on throughout the rest of the
house!
Where could series and
parallel connections be
used in cells?
Flashlights could use series circuits and cells. The more cells or
batteries to add to the circuit, the brighter the light bulb should
get! This is because connecting them in series results in higher
voltage and therefore, a larger current. If the cell were connected
in parallel, the cell would last longer but the light would be much
dimmer.
Lighthouses and remote controls are connected in parallel when it
comes to cells. This results in longer battery life, reducing
maintenance and battery costs!
Technology, function and
impact on daily lives
Fuses – a fuse contains a metallic conductor that melts when
excess current heats it up. This opens the circuit until the fuse is
replaced. This is a safety feature to ensure excess current doesn’t
reach devices and cause fire.
Circuit Breaker – Circuit breakers act as switches and a safety
device that can cut off all power into your home if the current
exceeds the amount able to be handled by the circuit. The breaker
will “Trip” and then you can reset it!
Grounding Terminals – The round prong on a 3 way plug is a
grounding terminal. The excess current will flow into the ground
instead of giving you a shock!
CORE Laboratory
Activity
Resistors in Series and Parallel
CORE Lab 9-1F
Electrical Energy
Energy that we use in our daily lives to run electrical devices such
as our lights and televisions. All energy refers to an ability to do
work.
Voltage is provided in 120 V and 240 V for use in homes. It is
supplied at a constant voltage for consumer safety and the safety
of electrical appliances
Joule
The unit used to measure energy. It is equal to 1 Newton x 1
meter and is named for the British scientist James Prescott Joule.
The symbol for joule is J and tells us how much work has been
completed.
Watt
A watt is a measure of electrical power and is equal to one Joule of
energy transferred in one second. It is named for the Scottish
inventor James Watt. The symbol for watt is W.
Electrical Energy Costs
depend on 3 factors
1. Voltage Drop – electrical stoves, heaters and dryers tend to run
on 220V and cost more to run whereas other appliances may run
on 110V.
2. Electrical current - Operating an electric toaster will cost more
than operating a radio for equal amounts of time even though they
both use the same voltage (110 V). This is because the current to
the toaster is much higher than that to the radio.
3. Time – objects that use more voltage and current that run for
longer periods of time will cost more to run
Formula for power
Power = voltage x current
=VxI
Power = watts (W)
Voltage = Volts (V)
Current = Amperes (A)
If we want to know how much power something uses we multiply
the voltage by the current it uses.
Calculating Power
1. How much power is being used by a 1200 volt saw that uses 0.5
A of current?
P=VxI
= 1200V x 0.5A
= 600 W
Practice Questions
1. What power is used by a 400 V refrigerator running at 3A?
2. Your scooter runs off a 12V battery and uses 2A of current.
How must power is your scooter using?
3. Our ROV has a 15 A fuse and is permitted to work at 12V.
What is its maximum power?
kWh
kWh is the symbol for kilowatt hour. It is a more convenient way
to measure electrical energy consumption. Our light bill from
Newfoundland Power shows our usage in kWh.
Most labels on appliances show their usage in kWh per year.
To calculate kWh we must have our power in kilowatts instead of
Watts and our usage time must be in hours.
Changing Watt to kW
To calculate kWh we must change our power to kWh from W. To
do so, we divide our W by 1000.
Example: 1200 W = 1200 ÷ 1000 = 1.2 kW
Calculating Energy
Consumption
To calculate energy consumption we are going to calculate how
many kWh are used by a particular item.
Energy Consumption (kWh) = Power (kW) x Time (h)
E=Pxt
Example 1: How much electrical energy is consumed by a 1.2
kW hair dryer used for 2 hours?
E=Pxt
E = 1.2 kW x 2 h
E = 2.4 kWh
Example 2: How much electrical energy is consumed by a 100 W
light bulb left on for 3 hours?
First, we need to change 100 W to kW so we divide by 1000.
100 W ÷ 1000 = 0.1 kW
Second, we can now do our formula.
E=Pxt
E = 0.1 kW x 3 h
E = 0.3 kWh
Example 3: How much electrical energy is consumed by a 1.4 kW
dryer that runs for 40 minutes?
First, in this example the power is ok but our time is not in hours.
So, we must change 40 minutes to hours.
40 min ÷ 60 min/h = 0.667 h
Now, we can continue with our calculations
E=Pxt
E = 1.4 kW x 0.667 h
E = 0.93 kWh
Remember: Sometimes you may have to change both the power
and the time before you can do the calculations
Practice Questions
1. Calculate the electrical energy used by a 1.5 kW appliance used
for 6 hours.
2. How much electrical energy is used by the toaster that uses 800
W and is kept plugged in for 2 hours?
3. What is the electrical energy consumption for a 1500 W washer
that is used to do one load of laundry that takes 45
minutes?
Determining Customer
Cost
Calculate the actual dollar value of using electrical appliances.
Once you have calculated the number of kWh you use, you
can now determine how much money you spend on
electricity using the charge from your electrical company.
For each of the Example questions above go back and recalculate
the $ cost using a price of 9.512 cents/kWh which is what
was used by Newfoundland Power in August of 2010.
Get each student to calculate the cost for the practice questions
above using 9.512 cents/kWh
Bring in a couple of electric bills from home. On the right hand
side it shows usage for this month and the same month last
year. Get students to calculate what you paid last year and
what you paid this year. Use the bill to show students how
Newfoundland Power calculates your usage in kWh and
how it comes up with your bill amount.
Electrical Energy is
converted to many other
forms
Electrical energy can be converted to:
1. Light energy – element on a stove turning red
2. Heat energy – heat is given off when you boil water
3. Sound energy – cracking sound of a pot when heated
The initial energy may come from electrical sources but it is
transferred into other sources of heat when it is needed
Calculating efficiency of
electrical devices
Given the amount of energy taken in by an electrical device and
how much energy it gives out, you should be able to calculate the
efficiency of an electrical device.
Example: An incandescent light bulb left on for 10.0 h/week uses
7.0 kWh of energy to supply 0.4 kWh of light. A compact
fluorescent bulb uses 2.0 kWh in the same amount of time to
supply the same amount of light.
% efficiency = Energy output x 100%
Energy input
Incandescent: 0.4 kWh x 100% = 6% efficiency
7.0 kWh
Compact fluorescent: 0.4 kWh x 100% = 20% efficiency
2.0 kWh
The compact fluorescent bulb is more efficient!
Practice Questions
1. Two light bulbs are kept on for 26 hours/week. One uses 5.0
kWh of energy and supplies about 0.75 kWh of light. The other
uses 2.5 kWh of energy to provide 0.5 kWh of light. Which is
more efficient?
2. You want to test the efficiency of 2 different types of light
bulbs. One package says that the bulb only uses 2 kWh of energy
and will produce 0.9 kWh of light. The other says that it uses 4
kWh of energy but will produce 1.9 kWh of light. Which bulb
should you recommend to others who want to be efficient?
Energuide and comparison
of appliances today and in
the past
A guide that uses labels on appliances to tell you the number of
kWh used by appliances in a year. It allows customers purchasing
products to make informed decisions about their energy
consumption.
Now use Energy Star labels
Natural Resources Canada Guide for Major Appliances Shipped in
Canada
http://oee.nrcanrncan.gc.ca/publications/statistics/cama08/pdf/cama08.pdf
Page 20 – Table 1.4 shows distribution of refrigerators by Average
Annual Unit Energy Consumption per cubic foot from
1990 to 2006. Students should see a huge and obvious
trend in the use of energy in the 16 years in the table.
Page 49 – Table 4.2 shows the distribution of Electric ranges by
Average Annual Unit Energy Consumption from 1990 to
2006. Students should see a huge and obvious trend in the
use of energy in the 16 years of the table.
Page 73 – Table 7.2 shows the annual unit energy consumption for
the 6 major household appliances from 1990 - 2006
EnerGuide Label
Energuide labels must be stuck on appliances for customers to
read.
Energuide labels are mandatory on all major appliances and air
conditioners.
Energuide labels must follow all Natural Resources of Canada
guidelines
Browse this website to look at the rules and regulations regarding
the mandatory and non-mandatory labeling
http://oee.nrcan.gc.ca/residential/business/energuide-labellingguide/mandatory-labelling.cfm?attr=12
Prepare a course of action
regarding energy
consumption
All students must brainstorm ideas that could help reduce the
amount of energy consumed in their own homes.
Examples include:
i) for homes heated by electricity, improve insulating factors
(ii) turn off lights when not required
(iii) use energy-efficient light bulbs
(iv) air dry clothes when possible
* Possible cross-curricular activity with language arts outcomes.
Students could write a persuasive letter to a parent, friend or
school principal that tries to get them to reduce the amount of
energy consumption in their environments
CORE STSE – Electricity
Conservation: The New
Trend
Students should complete the units CORE STSE at this point. It is
found in appendix A.
* Complete activity associated with the STSE.
Transfer and conversion of
energy
Recognize that energy transfers from one place or type to another
to be used. For example, wind energy - windmill generator utility lines - porch light.
Electrical generators and
their components: Coil and
Magnets
A device that is able to produce and distribute electrical energy.
Generators are designed such that either the coil of wire or
magnets move in relation to the other. This motion is achieved
through a number of sources. For example, the motion of water
and steam or portable gasoline generators (use mechanical
energy).
Types of electrical
generating stations
1. Hydroelectric – uses water to create energy. Churchill Falls is a
major source of hydroelectric energy in Newfoundland and
Labrador.
2. Thermal – generated using non-renewable fuels such as coal.
This can have devastating effects on the ozone layer
3. Nuclear – controlled reactions of the nucleus of different atoms
to produce new products. Nuclear reactions can be very
dangerous and cause serious cancer side effects if the
nuclear reactors happen to melt down. Further, it can
cause much environmental damage and release many
chemicals into the atmosphere
Electrical energy is transferred over very large distances using
high voltage but very low current
Electrical Energy
Transmission
Energy and the
Environment
Research Opportunity: Where do you get your power?
Look at safety measure, the cost of production and the degree of
environmental impact
Transformer
Transformers generally do one of two functions. They either step
up (increase) the voltage or step down (decrease) the voltage.
Power adaptors for various electric devices such as electric games
are examples of mini transformers that control the voltage going to
your system. Using the wrong adapter can send a surge of power
to your device and cause it to blow.
Alternate sources of
electrical energy
Factors influencing the
development of alternate
sources of energy
1. wind generator – converts kinetic (moving) energy of the wind
in to mechanical energy
2. solar energy – uses radiation, light and heat from the sun to
create energy
3. fuel cell - an electrochemical cell that converts energy from a
fuel into electrical energy
1. cost – may be too expensive to use the source or companies
want to use cheaper energy sources to save money
2. availability of materials – often, the availability of specific
resources dictate the type of energy used in an area
3. properties of materials – the chemical or physical property of a
material may make it difficult to harvest or use