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ELECTRICAL PRINCIPLES AND TECHNOLOGIES
FINAL EXAM PREPARATION
Name: ____________________________ Homeroom: ______
STUDY GUIDE
TYPES OF ENERGY AND ELECTRICAL ENERGY CONVERSION
(Textbook pages 288-331)
Energy Types
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Energy is the ability to do work or cause change.
The five main energy tasks are: light, heat, movement, growth and technology.
Energy comes in many different forms, including mechanical, chemical, thermal (heat),
light (radiant), nuclear and electrical.
Mechanical Energy Puts things in motion such as turbines or our bodies.
Chemical Energy Energy stored in chemical bonds, comes from food, wood, coal and
petroleum - can be burning, photosynthesis, cellular respiration, etc.
Electrical Energy The energy of moving electrons, static or current
Thermal (Heat) Energy Energy of moving or vibrating molecules - anything that gives
off heat has thermal energy
Radiant (Solar) Energy
Energy from the sunlight
Nuclear (Atomic) Energy Energy released from the atom nucleus – nuclear fission or
fusion
Converting Other Forms of Energy into Electricity

Mechanical energy transformed into electrical energy
 Generators
 In a hand-held generator, you spin the handle and this spins a coil of wire past
magnets. Electricity is induced into the wire and it can be used to power loads.
 In large scale power generating stations, the same principle is used. Massive coils of
wire are turned inside of huge magnets. The wire coil is turned by attaching it to
the shaft of a turbine (spinning shaft with blades attached). Electromagnetic
induction occurs when the electrical energy is induced into the wires.
Large Power Plant Generator.
Small Generator

A power grid moves electrical energy produced at a power plant to homes and
businesses. It uses large transmission towers to carry tremendous amounts of
energy. This energy is then “stepped down” to lower energy that is safe to use for
everyday tasks by using a transformer.
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Electrical energy to magnetic energy
 Electromagnet – a metal (usually iron) core with current carrying wire around it
becomes a magnet.
 Electromagnets are better than permanent magnets because they can be controlled
(shut on and off) and they can be made stronger or weaker (increase voltage or
number of wire coils).

Electrical energy is transferred into mechanical energy through a
motor.
Name of Part
Function of Part
Terminals
Carry current from source into motor
Brushes
Carry current to commutator
Commutator
Split ring reverses direction of current
flow to armature
North/South
Attract and repel the armature
magnets
Armature
Electromagnets on each end cause it to spin
as it is alternately attracted and repelled
by permanent magnets.
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Thermal energy to electric energy
 Thermocouple
 When different metals are subjected to heat on one end and
cold on the other, electrons become agitated and move. These
moving electrons generate a current in a circuit that is attached
to the metal. The greater the difference in temperature, the
more current a thermocouple generates. Metals must be
different or there is no potential difference (voltage) set up.
 The spinning armature is
attached to a shaft that
can turn wheels, fans,
etc.
 To make motor stronger,
use stronger source,
more coils on armature,
stronger permanent
magnets.
 To reverse motor
direction, change the
connections around on
the battery terminals or
change the direction of
the permanent magnets.
This is referred to as
changing the polarity
(direction of current
flow).
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Chemical energy to electrical energy
 Cells and batteries
 An acid (electrolyte) and base react to create voltage.
 A simple flashlight converts chemical to electrical energy and then electrical energy
to thermal, and then to light energy.
 Cells (wet or dry) have two electrodes which are metals of different reactivity (zinc and
copper, for example). The greater the difference in reactivity between electrodes, the
more voltage the cell creates.
 Cells have an electrolyte which is an ion solution that can conduct electricity. The
stronger the electrolyte, the more voltage the cell will produce. Saltwater or acid are
examples. The stronger the electrolyte, the more voltage the cell can produce.
 Basic cells like the ones you buy in the store are 1.5 V. More than one cell can be
combined to form a battery. Ex. Two 1.5 V cells make a 3 V battery.
 Wet cells and dry cells are similar but the electrolyte is liquid in a wet cell and paste in a
dry cell. Dry cells are used more for portable, continuous, longer lasting energy while wet
cells are more for a powerful initial electrical boost such as the one used to start an
automobile.
Direction of current flow
Wire
WET CELL
V
Negative terminal
Liquid
Electrolyte
DRY CELL
Positive terminal
Zn
Cu
Electrodes
Positive terminal
(copper)
Electrolyte
Paste
wire
V
Negative terminal
(zinc)
Direction of electron flow
CONTROLLING ELECTRICAL ENERGY (Textbook pages 275-302)
Dangers of Electricity
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A short circuit occurs whenever electricity bypasses the normal pathway in a circuit. When
you become that pathway, you are electrocuted. If wire is the pathway, it becomes very hot.
Amperage is the current that actually flows through your body so high amperage is very
dangerous. Voltage is the “pressure” that it is pushed with so although it is dangerous, it
doesn’t do the damage that current does.
A few hints – jump from a car with a downed power line, don’t step out. Don’t be the tallest
thing around or under the tallest thing around during a lightening storm. Groundwires (wires
leading electricity into the ground and away from where it could do harm) should never be
removed. Avoid frayed wire. Don’t overload a circuit. Unplug appliances before fixing them
Circuits are designed to carry only a certain amount of amperage. If more passes through
the wires, they become too hot. Fuses and circuit breakers are designed to keep this from
happening. A fuse may be 1 amp, 2 amps, etc. If it is 1 amp, it will melt and shut off the
circuit if devices requiring more than 1 amp are turned on. It then needs to be replaced with
a new fuse. Circuit breakers are similar but they have a switch that shuts off and can then
be turned back on so they don’t need to be replaced. For example, let’s say you have a 15
amp circuit breaker. You could add a 7 amp heater and a 3 amp drill. However, if you tried
to plug in a 6 amp fan, that would be more than 15 amps so the circuit breaker would flip and
your power would be shut off. You would unplug one of the devices before it would work.
Static and Current Electricity
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Static electricity is a stationary change that builds to a point where it suddenly discharges.
Positively charged particles (missing an electron) attract negatively charged particles (one
too many electrons). Lightening is an example, as is static cling. Materials with atoms that
are oppositely charged will attract one another while materials with atoms that are the
same charge will repel one another. Any charge atom is attracted to an opposite or a neutral
charge.
Current electricity is a steady flow of charged particles through a conductor (a circuit). It
flows until its source is cut off. All of our electrical devices use current electricity, for
example, flashlights and motors.
Conductors and Insulators
Examples
Conductor
Insulator
Semiconductor
Superconductor
Resistor
Characteristics
Uses
Metals (copper)
Ionic solution
Rubber, glass, air
(non-metals)
Carbon, silicon
Material that conducts electrical energy (allows current to
flow) because it loses electrons easily.
Material that does not allow the flow of electricity
through it because the atoms do not easily lose electrons.
Properties of both conductors and insulators.
Used in circuits
to conduct electricity
Protection from
electrical shock
Microchips
Extremely cold
metals
Almost perfect conductor (almost no resistance to flow)
M.R.I.s
Nichrome and
Tungsten wire
Conductor that resists the flow of electricity. It retains
the energy and heats up rather than letting it pass.
Light bulbs, heaters,
dimmer switches
Technology Using Resistors
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Lie detectors work on the principle of resistance and conductivity. When people lie they
sweat. Sweat is saltwater which is a good conductor so the machine registers decreased
resistance (increased conductivity) when someone is lying.
Light bulbs work by using a resistor as the filament (the thin wire inside the bulb). By
making a material like tungsten as long and thin as possible, it makes it very difficult to
electrons to pass so they heat up through friction. They heat so much that the metal
filament glows, and we use that as our light source.
Toaster or other heaters are similar. There are coils inside a toaster of high resistance
wire. When the toaster is turned on, the coils heat up because of their increased length
due to coiling and their high resistance. The heat is used to toast bread.
Switches
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Switch on – metal contacts wire so circuit is complete and electricity flows.
Switch off – metal does not contact wire so circuit
is incomplete - electricity does not flow.
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Simple circuit switch
When this switch is closed the light goes
on. When it is open as it is in this picture,
the light stays off.
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Rheostat, variable resistor or dimmer switch
Usually uses resistive wire such as nichrome or
semiconductor such as carbon. If current flows through
more of the resistor, the light dims because energy is going
to the resistor (it heats up). If it goes through less resistor,
the light brightens so you can control brightness. The more
the light dims, the greater the resistance in the circuit. You
can also test how resistant a material is by seeing how much
the light dims. Rheostats can be used to control brightness,
volume, speed (motor) and temperature (heater).
Rheostat Circuit Diagram
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2 or 3-Way Switch
This allows you to turn lights on and off at different locations,
for example the top and bottom of stairs.
On
Off
Switch
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A photocell is a device that acts like a switch when it is activated by light
energy. A common use is when a door seems to open by itself when we
approach it. This happens because our body blocks a beam of light and a
photoelectric cell makes the door open. It is also commonly used for
security alarms. The photoelectric cell is often referred to as an “electric
eye”.
CURRENT, VOLTAGE AND RESISTANCE
(Textbook pages 304-308)
Voltage
The pressure that pushes electrons in an electrical circuit is called
voltage.
Using the water analogy, if a tank of water were suspended one meter
above the ground with a one-centimeter pipe coming out of the bottom,
the water pressure would be similar to the force of a shower. If the
same water tank were suspended 10 meters above the ground, the
force of the water would be much greater, possibly enough to hurt you.
Voltage (V) is a measure of pressure, or electromotive force, applied to
electrons to make them move. They move with more force when you use
a 12 V battery than they do with a 1.5 V cell. Household voltage is 120.
Current
The flow of electrons can be compared to the flow of molecules of
water. The water current is the number of molecules flowing past a
fixed point; electrical current is the number of electrons flowing past a
fixed point. Current is measured in amperes or amps (A). With water,
as the diameter of the pipe increases, so does the amount of water
that can flow through it. With electricity, a conducting wire is the pipe.
As the cross-sectional area of the wire increases, so does the amount
of electric current (number of electrons) that can flow through it. The more loads
you put on a circuit, the more current will flow to supply the loads with energy.
Resistance
Resistance is a property that slows the flow of electrons––the
current. Using the water analogy, resistance is an impediment to
water flow. It could be a smaller pipe or fins on the inside of a pipe.
In electrical terms, the resistance of a conducting wire is
dependent on the metal used to make the wire, and the diameter of
the wire. The thinner the wire, the higher the resistance. Heat also
increases resistance, as does length of wire. Resistance is measured
in units called ohms Ω). There are electrical devices, called
resistors, designed with specific resistance that can be placed in
circuits to reduce or control the flow of the current (lights, for
example). These are called loads.
Ohm’s Law
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Ohm discovered that current flowing through a material is proportional to the
voltage. If you double voltage, current also doubles. Resistance, on the other
hand, remains the same. This is called Ohm’s Law. It states that R = V/I
Current (I) is
measured in
Amps (A)
Voltage is
measured in
Volts (V)
Resistance is
measured in
Ohms (Ω)
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Measures amount of electrical current.
Most household devices have low amperage.
Measure of how much electrical energy
each charged particle has. Household
voltage 120 V, Cells 1.5 V.
Measures how difficult it is for electricity to
flow. Nichrome wire has high resistance
while copper wire has low resistance.
Measure using an ammeter (measures
exact current) or a galvanometer
(measures very low currents).
Measure using a voltmeter.
Measure using an ohmmeter.
Multimeters can be used to measure all three properties with one instrument.
Ammeter for current
galvanometer
(scale 2 amps)
Voltmeter for voltage
(scale 1 volt)
Hand made
SERIES AND PARALLEL CIRCUITS
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(Textbook pages 311-315)
Series Circuits - each component has the same current. The battery voltage is divided
between the loads. Each load will have half the battery voltage if the loads are identical.
Parallel Circuits - each component has the same voltage. Both loads have the full
battery voltage across them. The battery current is divided between the two loads.
The terms series circuit and parallel circuit are sometimes used, but only the simplest
of circuits are entirely one type or the other. It is better to refer to specific
components and say they are connected in series or connected in parallel.
Series
Cells in Series
Parallel
Circuit Diagram
Symbols for Cells:
Series (3 V)
Cells in Parallel
Parallel (1.5 V)
SERIES
Example
Description
Flashlight
Current
passes
through
each load in
turn so
voltage is
shared
Separate
current for
each path
so each
load gets a
full share
of voltage
Switches in
homes
PARALLEL
Household
wiring
Most tree
lights
Adding
loads
Each added
load means
less
voltage for
others so
lights dim
Removing
loads
When one
load burns
out, others
all go out
since circuit
is broken
No
difference
since all
loads get
full amount
of voltage
Other loads
stay on since
they have a
separate
conductor
back to
source
Adding cells
Advantages
Disadvantages
Cells added in
series result
in added
voltage (i.e.
two 1.5 V
cells add up
to 3V battery
Cells added in
parallel do
not increase
voltage but
they do make
each cell last
longer
Simple to
construct
Circuit all
goes off if
one load burns
out
Uses less
energy
Flexibility in
operating
loads
together or
separately
More complex
to construct
Use more
energy
Decide which of these
circuit diagrams would
have the brightest bulbs.
Think about the type of
circuit, number of cells,
and number of loads when
deciding.
A, B, C and F would all be
about the same
brightness. Although A
has only one cell, it also
has only one bulb. B, C and
F all have two cells and
two bulbs in a series
circuit. In E, the bulbs
would be more dim since
there is an extra load but
no extra cell. D is a
parallel circuit and it
would be the brightest
since each bulb is getting full voltage from the two cells.
Microcircuits
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Resistors in microelectronic circuits do the same thing as in regular circuit – control how
much current is allowed to flow through a certain part of the circuit.
Transistors are used as switches in tiny microcircuits. They can stop or start current in
several different directions at once. They basically do the same thing as switches in
larger circuits.
Circuit Diagram Symbols
Component
Circuit Symbol
Lamp (lighting)
or
Motor
or
Cell
Function of Component
This symbol is used for a lamp providing
illumination, for example a lightbulb.
A device which converts electrical energy to
kinetic energy (motion).
Supplies electrical energy. Single cell (1.5 V)
Supplies electrical energy. A battery is more
than one cell. This one represents an
unknown number of cells.
Another symbol for a battery that defines
number of cells. This is a 4.5 V battery.
Battery
Battery
A photocell. Light will either turn a circuit
with this cell on or off.
Photocell
Wire
To pass current very easily from one part of
a circuit to another.
A voltmeter is used to measure voltage.
Voltmeter
Ammeter
An ammeter is used to measure current.
An ohmmeter is used to measure resistance.
Most multimeters have an ohmmeter setting.
Ohmmeter
Resistor
Another common symbol used for resistors
Variable Resistor
Used to adjusting lamp brightness, adjusting
motor speed, and adjusting the rate of flow.
An on-off switch allows current to flow only
when it is in the closed (on) position.
On-Off Switch
EFFICIENCY AND POWER

(Textbook pages 332-338)
Input energy is the amount of energy you start with and output energy is how much
energy actually goes toward the job you are trying to do.
Input energy
Mechanical
Output energy
Electrical
Device
Generator
Chemical
Electrical
Cell or battery
Electrical
Chemical
Thermal
Electrical
Chemical
Light
Mechanical
Electrical to thermal
Electrical
Thermal
Mechanical
Electrical
Motor
Light bulb
Thermocouple*
Oven
Digestion
Photocell
Efficiency Calculations
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Efficiency refers to how much energy you into doing a job, relative to how much work
actually gets done. No machine is 100% efficient since energy is lost through sound,
motion, and especially heat (due to friction). Incandescent bulbs are 5% efficient
meaning 95% of input energy is lost to heat and only 5% goes to light energy (output).
Fluorescent bulbs are a bit better at 20%.
Ef = Eo / Ei x 100
Efficiency = Energy output divided by Energy Input times 100
The unit for efficiency is %. The smaller the percent, the less efficient the device.
For example, you are using a gasoline powered trimmer on the grass. You will need to
add 2100 joules of energy from the gasoline in order to get 700 joules of useful work
from the trimmer. What is the efficiency of the gas trimmer?
Ef = Eo / Ei x 100
Ef = 700 / 2100 x 100
Ef = 33.3 x 100
Ef = 33%
Power Calculations
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Electrical power is the rate of doing work or the rate at which energy is
converted. Using the water analogy, electric power is the combination of the
water pressure (voltage) and the rate of flow (current) that results in the
ability to do work.
Electrical power is measured in watts (W). The formula for power is
P = I x V (Power = current times voltage).
For example, you are using a drill that draws 12 amps from a 6 volt battery. How much
power is consumed by this drill?
P=IxV
= 12 x 6
= 72 watts
A kilowatt hour is a measure of power. It is a unit for measuring large amount of
electrical power use per hour, such as at your house.
Energy Calculations
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Energy is the ability to do work. It is measured in joules (J).
Energy = Power times Time (E = P x t)
For example, you turn on a 100 watt bulb in your bedroom and leave it on for 1 minute.
How much energy was transformed?
E=Pxt
= 100 x 60 (remember to always convert time to seconds)
= 6000 joules (or 0.6 kJ or 0.0006 MJ) MJ = megajoule kJ = kilojoule
Saving Energy
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There are lots of things that people can do to reduce energy waste. For example,
use more efficient types of light bulbs, don’t over dry clothes, don’t use an entire
wash cycle for a pair of socks, reduce friction by lubricating machines, insulate
appliances like dryers and fridges to avoid heat loss, turn off the lights!
Energuide labels help us increase efficiency by showing us which devices are the
most efficient before purchasing them. The label tells the average number of kWh
it would use in a year and compare its efficiency on a scale with other models.
ALTERNATIVE WAYS TO PRODUCE ELECTRICITY
(Textbook pages 345-358)
Source
Fossil fuels (coal, oil, natural gas).
Most of Alberta’s energy is from
burning coal. The fire heats steam
that then turns a generator turbine.
Wind/Waves. The wind or water
turns blades on a turbine attached to
an electrical generator.
Hydro. Water falling over a dam
turns a turbine attached to
generator.
Biomass. Trees, agricultural waste,
manure, sewage, scrap wood from
construction, etc. When burned, this
heat water to steam that then turns
a generator turbine.
Battery-power. These would be
lead-acid batteries.
Advantages
Relatively cheap,
technology is already
in place.
Disadvantages
Non-renewable, pollution from
burning fossil fuels is dangerous for
the environment.
Renewable ,clean
Location - limited
Renewable, clean.
Location is limited. Destroys
habitat and affects natural course
of river.
The burning does produce some
sulfur dioxide and nitrogen oxide
(acid rain) but far less than fossil
fuels.
Solar. Solar panels convert radiant
(light) energy to electrical energy.
Nuclear. Nuclear generators create
to turn steam turbines.
Renewable, clean.
Renewable resource.
No burning, no
emissions
Clean, very efficient.
Nonrenewable, lead and acids from
batteries adds toxic waste to
landfills
Location is limited. Expensive.
Takes up lots of space.
Radioactive waste material to
dispose of.
We want to find a way to produce electricity that will be both clean and sustainable (able to
last well into the future). A tremendous amount of research is currently going into this.
Pollution from Fossil Fuels

Most electricity in Alberta is generated from burning coal. Byproducts include:
 Sulfur dioxide –causing acid rain.
 Nitrogen oxide –causing acid rain.
 Carbon dioxide – greenhouse gas causing global warming
 Fly ash (very fine dust) contains mercury and arsenic which are poisons.
Benefits of Electricity



Electricity is used for heat, light, movement and communication.
Binary system – electrical systems communicate using two numbers – 0 and 1. Basically,
0 is off and 1 is on. The microcircuits in the electrical system are told to turn on and
off in order to create a code that can be translated into usable information.
One of the most recent technologies has been in the field of communication. Computers,
and especially the internet have allowed us to become a single, global community.
Benefits – better understanding of the world, ability to do business without having to
travel great distances, saves time, opens up a world of information that was not
available before. Drawbacks – your personal information, including financial
information, is easily available to those who know how to get it, you are never sure who
you are “talking” to.
ELECTRICAL PRINCIPLES VOCABULARY REVIEW
1. Electricity that is stationary until it builds to a high enough energy level to
suddenly discharge is called static electricity.
2. When electricity flows as a steady stream of charged particles through a
conductor it is called current electricity.
3. Current electricity always wants to take the shortest pathway and when it
gets a chance to do this through a conductor other than its normal path
(including through you if you get in the way), it is called a short circuit.
4. Voltage is the energy of each charged particle (its strength) and it is
measured in volts using a voltmeter.
5. Amperage is the rate at which charged particles move (how many pass a
point in a given time) and it is measured in amps using an ammeter or a
galvanometer.
6. Groundwires are designed to give electricity a pathway away from people and
down into the ground in case there is a short circuit.
7. Fuses are designed to melt if too much current passes through them. This
keeps a circuit from heating up to the point where it could start a fire.
8. Circuit breakers in buildings have switches that flip off if a metal strip
bends too much through excess heat. This shuts the circuit off before it
can get too hot and cause a fire.
9. Cells are designed to convert chemical energy into small amounts of
electrical energy.
10. All cells have two different metals making up their electrodes and an ionic
conductor (acid or base) called the electrolyte which is in contact with the
metal strips.
11. Two or more cells connected together is called a battery.
12. Wet cells have an electrolyte in paste form and dry cells have an electrolyte
in liquid form.
13. Energy always flows from the negative terminal toward the positive terminal
in a cell.
14. Materials such as copper that easily allow the flow of charged particles are
called conductors.
15. Materials such as rubber that do no allow the flow of charged particles are
called insulators.
16. Materials such as silicon that have properties of both resistors and
conductors are called semiconductors.
17. Super conductors are almost perfect conductors at very cold temperatures,
offering little or no resistance to current flow.
18. A conductor that is more difficult to flow through and therefore uses up
more energy, such as nichrome or tungsten wire, is called a resistor.
19. The unit for measuring resistance is the ohm and it is measured using an
ohmmeter.
20. A rheostat or variable resistor allows a load in a circuit to have varying
amounts of electrical energy so lights will dim and brighten, speakers will get
louder and more quiet and motors will go faster and slower.
21. A schematic diagram of the components making up an electrical circuit is
called a circuit diagram.
22. Every circuit must have at least one energy source, a conductive pathway for
current, a load which converts electrical energy to another form of energy
and a switch to start and stop the current.
23. A circuit that has all loads in succession along one pathway is called series.
24. A circuit where each load has its own pathway back to a source is called
parallel.
25. Micro resistors (control amount of current flow) and transistors (act as
complex switches) are the primary parts of electronic circuits.
26. Some common sources of energy that can be converted from one form to
another are electrical (energy of charged particles), chemical (energy of
chemical reactions), mechanical (energy of moving objects) or thermal
(energy of heat).
27. A device that can convert thermal energy into electrical energy by heating
two different kinds of metal is a thermocouple.
28. A magnet that can have its power turned on and off or made stronger or
weaker by current is called an electromagnet.
29. Faraday discovered electromagnetic induction when he moved a magnet
through a coil of wire and voltage registered in the circuit.
30. An electric motor converts electrical to mechanical energy.
31. The parts of a motor are the brushes (carries current from source into
motor), the commutator (alternately switches polarity of current flow to the
electromagnets), the armature (spins and turns attached mechanisms) and
the permanent magnets (attracts the electromagnets on either side of the
armature).
32. You can change the direction a motor turns by changing the polarity. This is
done by reversing the terminals.
33. A generator converts mechanical energy into electrical energy through
electromagnetic induction.
34. In Alberta, coal is burned and used to create steam which turns a turbine
which then turns magnet or wire inside the generator. The electricity
generated is sent on to homes and businesses. This is all part of our power
grid.
35. The rate at which energy is converted is called power and it is measured in
watts, kilowatts (1000 watts) or megawatts (1 000 000 watts).
36. Energy is the ability to do work and it is measured in joules, kilojoules (1000
joules) or megajoules (1 million joules).
37. For convenience in determining the amount of energy used by households and
businesses, meters are set to read kilowatt hours rather than joules but
they are calculated the same way.
38. The efficiency of most light bulbs is not very good because a great deal of
the input energy goes to producing output heat energy rather than light.
39. Incandescent bulbs are only 5% efficient while fluorescent bulbs are better
at 25%.
40. Rather than burning fossil fuels to produce steam, some cleaner alternative
energy sources include geothermal (heat from earth’s core), nuclear (heat
from splitting atoms), biomass (heat from rotting garbage) or solar (light
from sun).
41. Sustainability refers to the choice to use resources in a responsible manner
so that they will be available to future generations.
42. A device that uses the fact that sweaty skin is more conductive than dry
skin in order to tell if a person is being truthful is called a lie detector.
43. Nichrome wire and tungsten wire (used in light bulbs) are both resistors
used in many electrical devices.
44. The mathematical formula V = I x R is called Ohm’s Law.
45. The energy required to make an electrical device operate is called the input
energy while the amount of useful work you get out of it is called output
energy.
46. All appliances must have an energuide label to let consumers know how
efficient it is.
47. Producing electrical energy can pollute the environment through chemicals
such as sulfur dioxide (produces acid rain) and carbon dioxide (greenhouse
gas).