Electric Motors

Document technical information

Format doc
Size 157.2 kB
First found May 22, 2018

Document content analysis

Category Also themed
not defined
no text concepts found


Thomas Johann Seebeck
Thomas Johann Seebeck

wikipedia, lookup




Unit 4 -Electrical Principles and Technologies
Lesson 1 – Electrical Charges
 Materials that attract and repel other materials are
said to be charged, or carry an electric charge.
 A neutral object has the same number of electrons as
protons. When a neutral object gains electrons, it
becomes negatively charged; when it loses electrons, it
becomes positively charged.
 Note: only electrons move. Protons do not because they
are inside the nucleus.
 Static electricity means electricity “at rest”.
 Law of Charges:
1. Unlike charges attract.
2. Like charges repel.
3. Charged objects attract neutral objects.
Conductors, Insulators, and In-Between
Materials that allow charges to move are called
conductors – metals are good conductors.
Materials, which do not conduct electricity well, are called
insulators – rubber, non-metals are good insulators.
 Semiconductors are materials with higher conductivity
than insulators but with lower conductivity than metals.
Ex. Silicon.
 Superconductors are materials that offer minimal
resistance to the flow of electrons. However, most of
these materials must be cooled to near absolute zero
(- 273.150C) to become superconductors.
Ex. Alloys and ceramics.
Neutralizing Unbalanced Charges
 One practical way to neutralize charged objects is by grounding.
Grounding allows the excess electrons to flow into the earth.
 We ground the electrical panel in the basement to the water
main, which is buried in the earth to maintain electrical
neutrality within the home.
Lesson 2 – Electricity within a Circuit
 An electric circuit provides a continuous path for
electrons (charges) to move.
 All circuits have four basic components:
1. Source: produces electricity. Ex. a battery
2. Conductor: wires.
3. Load: uses the electricity. Ex. light bulb
4. Control: switches.
A cell is a device for producing electricity from chemical or
solar energy. A battery is a combination of cells.
Common electrical symbols
Conductor (wire)
Variable Resistor
Current and Voltage
 Electric current refers to the flow of electrons
(charges). It is measured in amperes (A).
 An instrument used to measure very weak currents is
called a galvanometer. Larger currents are measured
with an ammeter.
 The energy for pushing electrons through a circuit
comes from a battery or generator. For the electrons to
move they must have more energy at one terminal than
the other. This difference in energy is called potential
difference or voltage.
 Voltage is measured in volts (V). A voltmeter is used to
measure voltage.
Lesson 3 – Resisting the Movement of Charge
- Resistance is a measure of how difficult it is for
electrons to flow through a conductor
- If the resistance is high the energy of the electrons
(voltage) gets converted to heat and light - like in a
filament of a light bulb.
- Current in a circuit can be either controlled by
adjusting the voltage or resistance
- The unit for resistance is the ohm.
- Symbol is Ω, omega.
Ex. 5 Ω means “resistance is 5 ohms”.
- We can measure resistance using an ohmmeter or a
- Variable resistors or rheostats are used to control
the amount of current in a circuit. Ex dimmer switches,
volume controls on stereos.
Calculating Resistance
- Electrical resistance is calculated using the formula:
V = voltage in V
I = current in A
R = resistance in Ω
- This relationship is known as Ohm’s Law.
- Rearranging the formula to:
 Find Voltage use:
V = IR
 Find Current use:
Examples of Problems
1. A current of 0.5 A flows through a lamp when it is
connected to a 120 V source. What is the resistance
of the lamp?
Given: I = 0.5 A
V = 120 V
Find: R = ?
R = V = 120
R = 240 Ω
2. A resistance of 30 Ω is placed across a 90 V battery.
What current flows in the circuit?
Given: R = 30 Ω
V = 90 V
I = V = 90
R 30
3. A motor with an operating resistance of 15 Ω is
connected to a power source. If the current in the
circuit is 4 A, what is the voltage of the source?
Given: R = 15 Ω
V = IR = (4)(15)
V = 60 V
Factors Affecting Resistance of Wire
1. Length – the longer the wire the higher the resistance.
Electrons have to travel longer, thus more chances for them to
bump into each other.
2. Cross-sectional Area – the greater the area the lower the
resistance – more room for electrons to move. This
“thickness” is commonly described by an American Wire
Gauge (AWG) number.
3. Temperature – the higher the temperature the higher the
resistance – temperature increases the kinetic energy of
4. Material – some materials allow electrons to move more
freely than others.
Assignment: pg 291 #1 - 8
Assignment 3 : Ohm’s Law - Show your work
1. What current flows between a potential difference of 120 V through
a resistance of 30 ?
2. A voltage of 75 V is placed across a 15  resistor. What current
flows through the resistor?
3. A current of 0.5 A flows through a lamp when it is connected
to a 120 V source. What is the resistance of the lamp?
4. A resistance of 60  allows 0.4 A of current to flow when it is connected
to the terminals of a battery. What is the voltage of the battery?
5. A radio uses 0.2 A of current when it is operated by a 3 V battery.
What is the resistance of the radio circuit?
6. A diagram shows a circuit that indicates a 90 V battery, an ammeter, and a resistance
of 12.5 . What does the ammeter read? (Find current).
7. A circuit diagram has a 16  resistor, a battery, with an ammeter
that reads 1.75 A. Find the voltage of the battery?
8. What voltage is applied to a 4  resistor if the current is 1.5 A?
9. A 20  resistor is connected to a 30 V battery. What current flows through the resistor?
10.A lamp having a resistance of 10  is connected across a 15 V battery. What current flows
through the lamp?
11.A bulb of 15  is in a circuit across a 4.5 V battery. What is the current in this circuit?
12.A heater draws 10 A from a 120 V source. What is the heater’s resistance?
p. 282 #1 – 4 (do on loose leaf)
Lesson 5 – Voltage, Current and Resistance Lab
p. 284
Lesson 4 – Electric
 There are two types of circuits: series and parallel.
 Series circuits have only one current path – the
current is the same at all points along the wire.
The electrons flow from the battery along a single
pathway and back to the battery. The more devices or
lights in a circuit the weaker each becomes as the
energy available from the electrons is being shared. If
one light bulb is removed none of the lights will work
because the circuit is broken and the electrons cannot
 Electrons flow from the negative to the positive
 Parallel circuits have several current paths – several
branches connected side by side. The electrons come
from the battery and travel along alternate pathways
and back to the battery. Only some of the electrons
will pass through each device in the circuit. If one
light bulb is removed the others continue to work.
The number of lights in the circuit does not affect the
brightness of the lights.
You can keep
adding resistors.
 House wiring uses parallel circuits – if one resistor
(light) burns out the current in the others is not
 To guard against electrical fires, which may occur if
wires become hot enough, household circuits have
fuses or circuit breakers.
Factors Affecting Resistance of Wire
1.Length – the longer the wire the higher the
resistance. Electrons have to travel longer, thus more
chances for them to bump into each other.
2.Cross-sectional Area – the greater the area the lower
the resistance – more room for electrons to move. An
American Wire Gauge (AWG) number commonly
describes this “thickness”.
3.Temperature – the higher the temperature the higher
the resistance – temperature increases the kinetic
energy of electrons.
4.Material – some materials allow electrons to move
more freely than others.
Lab - Lamps in a Series and Parallel Circuit
(reference p. 287)
QUESTION How does adding extra bulbs
the other bulbs in a series or parallel circuit
*** Fill in predicted values before doing the lab.
Predicted Observed Current
brightness brightness (A)
1 bulb
2 bulbs
3 bulbs
3 bulbs,
2 bulbs
3 bulbs
3 bulbs
Observed Current
brightness (A)
Seen by
Seen by
1. How does the brightness of the bulbs change as more bulbs are added to the
series circuit? How did the electric current as measured by the ammeter change?
2. How does the brightness of the bulbs change as more bulbs are added to the
parallel circuit? How did the electric current as measured by the ammeter
3. Using your results, explain why the brightness of the bulbs changes in the series
circuit. Use your knowledge of Ohm’s Law and resistance to answer the
4. Using your results from the parallel circuit explain any changes or lack of
changes in the brightness of the bulbs.
5. What happened to the series circuit when one of the bulbs was unscrewed?
Explain why.
What happened when one of the bulbs was unscrewed in the parallel circuit?
Explain why.
Lesson 5: Electricity and Heat
 Heat can be converted directly to electric energy
using a device called a thermocouple.
 A thermocouple is a loop of two wires made of
different types of metals. The wires are wrapped
together at both ends, called “junctions”.
(See p. 294)
When one junction is heated, a small electric
current is produced. If the temperature is
increased, the current increases. Thomas Seebeck
discovered this principle in 1821. This is called
the Seebeck Effect.
 A thermo-electric generator is a device based
on a thermocouple that converts heat directly
into electricity.
 Heat from a gas burner moves through several
thermocouples connected in series, called a
thermopile, creating a potential difference.
Electricity and Motion
 Some crystals such as quartz will produce a
sound when an electric current passes through
them. This phenomenon is called the
piezoelectric effect.
Ex. Sound produced by tiny electric watches or
greeting cards.
A barbecue “spark” lighter uses the piezoelectric
effect in reverse. When the crystal is being
compressed an electric current is produced.
Electricity and Light
 One of the most common uses of electricity is to
produce light - using light to produce electricity might
be the way of the future (no pollution).
 Photovoltaic (PV) cells, or solar cells, are used to
convert light energy to electrical energy.
Electrochemical Cells
 All chemical cells have two features in common. One
is the presence of two different metals called
electrodes. The other is the separation of the metals
by a substance called electrolyte.
 The electrolyte can be a liquid, a “wet cell”, or a solid
(most likely a paste), a “dry cell”.
 The chemical reactions in a cell determine the voltage
that the cell can create. Single cells usually produce a
maximum of 2 V. To get higher voltages several cells
connected in series are used (battery).
 If a cell cannot be recharged, a primary cell, the
amount of chemicals it contains determines the
energy the cell can produce.
 Rechargeable secondary cells use chemical reactions,
which can be reversed. In a re-charger, electricity is
forced through the “dead” cell, rebuilding the original
chemicals and allowing the cell to be reused.
Lesson 6 - Generators and Motors
 The principle behind generators and motors is the relationship
that exists between electricity and magnetism.
 Oersted and Ampere made the discovery of this relationship in
1820. Oersted observed that a magnetic (compass) needle turned
when it was near a current carrying wire.
 An electric generator is a device that converts mechanical
energy into electrical energy. A generator produces electricity
by rotating loops of wire, called armature, in a magnet.
 Most large generators use electromagnets instead of permanent
magnets. An electromagnet is a wire wrapped around a soft
core. When a current is passed through the wire a temporary
magnet is produced.
 As the wires rotate in a generator the electrons (electricity) begin
to move along the wire in one direction. As the coil moves
through the other pole of the magnet the electrons start moving
in the other direction. Thus, the direction of the current flowing
from the generator changes twice with each revolution.
 Electricity produced by this type of generator is called
alternating current (AC) because it changes direction, or
 In North America the cycle is set at 60 cycles/second
or 60 Hertz (Hz).
 Why AC current instead of DC? One reason is that it is easy to
increase or decrease the voltage of AC current. In order to travel
long distances efficiently through transmission lines, the voltage
is increased. For consumer use, it is then decreased.
DC Generators
 Direct current (DC), or current that flows in only one direction,
can also be produced by generators. A generator that produces
direct current is often called a dynamo.
 In a dynamo, the armature is connected to the outside circuit by
a split-ring commutator. (See Fig. 4.38A p. 314)
Electric Motors
 An electric motor converts electric energy to mechanical
energy. Same basic design as a generator.
 When the armature is connected to a source of energy it turns
into an electromagnet, which is rotated by magnetic forces from
the permanent magnet. The fundamental law of
magnets – opposite poles attract and like poles repel – is the
basis upon which electric motors function.
DC Motors
 DC motors use a split-ring commutator, which acts as a switch,
cutting off and then reversing the direction of current flow to
keep the armature turning. (See p. 315)
AC Motors
 AC motors have a rotating core, or rotor, made up of a ring of
non-magnetic conducting wires. Surrounding the rotor is a
stationary component called a stator. The stator is a two-pole
(north and south) electromagnet.
 When an AC motor is turned on, the attraction and repulsion
between the magnetic poles of the stator and the rotor causes the
rotor to spin. (Fig. 4.40 p. 317).
Lesson 7 -
Electricity in the Home
 Large electric generators in power stations produce
AC current for use in homes and industry.
 Transformers are used to “step up” the voltage for
efficient transmission over long distances. At the
destination, other transformers “step down” the
voltage to the 120/240 V used in homes and factories.
 In our homes the lines first go through a meter, then
through a circuit breaker (older homes might have a
fuse box instead). Fuses are common in cars and
electric stoves.
 Cables that contain three wires connect the breakers,
plugs, lights, and switches in each branch circuit.
There are two “live” wires – a white insulated wire
(usually called the neutral wire) and a black
insulated wire (usually called the hot wire). The third
wire, the ground wire, is either bare copper or
covered with green insulation.
 The black wire carries high-energy electricity through
the circuit. The white wire returns low-energy
electricity back to the breaker panel. The ground wire
reduces shock hazards.
 Home wiring follows strict regulations and must meet
a set of standards called the electrical code.
Measuring Electric Power
 Power is defined as energy per unit time.
Power (in watts) = Energy (in joules)
Time (in seconds)
 The units of power are joules per second. One joule
per second is equal to one watt (W) in honor of
James Watt (1736-1819).
 However, in electricity the formula for power is:
P = VI
V = Voltage in V
I = Current in A
P = Power in W
Rearranging we can find:
1. A current of 13.6 A passes through an electric baseboard
heater when it is connected to a 110 V wall outlet. What is
the power of the heater?
I = 13.6 A
V = 110 V
P = VI
P = (13.6)(110)
P = 1496 W
2. A 990 W oven requires 8.7 A of current to run. What is the
voltage of the circuit?
P = 990 W
I = 8.7 A
V = P = 990
I 8.7
V = 114 V
3. A 100 W light bulb requires 120 V to operate. What is
the current?
P = 100 W
V = 120 V
I = P = 100
V 120
I = 0.83 A
Measurement and Cost of Electrical Energy
- The unit of energy is the Joule (J)
- If a device uses energy at a rate of one Joule per
second that’s equal to one Watt.
1 J/s = 1 watt (W)
- The Joule is a very small unit for measuring energy, so
instead we use the kilowatt-hour (kW-h) to measure
large amounts of energy
1 kW-h = 3 600 000 J
- Power companies charge users by the kW-h
- Example: $ 0.09/kW-h or 9 cents per kW-h
Four steps to follow to solve problems
1. Always convert watts to kilowatts
(W to kW divide by 1000)
2. Convert time to hours (60 min =1 h)
3. Calculate kW-h (multiply the kW by the hours)
4. Calculate the total cost.
Total Cost = # of kW-h • cost/kW-h
1. A family uses 3000 kW-h of energy in a two-month period. If
the energy costs 11.0 cents per kilowatt-hour, what is the electric
bill for the period?
Total Cost = # of kW-h • cost/kW-h
= 3000 x 11 = 33,000 cents
= $ 330.00
2. A 60 W light bulb is left on for 5 hour and 40 minutes. If the
cost of electricity is 13 cents per kW-h what did leaving this
light on cost?
 First change the W to kW
60 W = 0.06 kW
 Next find the time in hours
5 h and 40 min. = 5.67 h
 Then find the # of kW-h
# of kW-h = 0.06 kW • 5.67 h
= 0.34 kW-h
Total Cost = 0.34 x 13 = 4.4 cents
3. A toaster is used an average of 5 h per month. The toaster
draws 8 A of current from a 110 V outlet. If electricity costs
8 cents per kW h how much will it cost to operate the toaster
for one year?
Step 1 – Find power (the watts)
P = IV
= 8 x 110
= 880 W = 0.88 kW
Step 2 – Find the energy in kW-h
= 0.88 kW x 60 h
= 52.8 kW-h
Step 3 – Find the cost.
Cost = kWh x $ 0.08/kWh
= 52.8 x 8
= 422 cents = $4.22
Lesson 8: Power Rating
 Many electric appliances have a power in watts
marked on them. This rating tells you how many
joules of energy the device uses every second of
operation (1 W = 1 J/s).
Ex. A 100 W light bulb uses 100 J of energy every second.
 If a light bulb were perfect, all of the electric energy it
took in (input energy) would be converted into light
(useful output energy).
 Since no device is perfect some energy is always wasted, that is
no device is perfect or 100% efficient.
To find efficiency we use the formula:
Efficiency = energy output
energy input
x 100%
Efficiency = output x 100%
If power and time are given to find energy use:
Energy = Pt
E = Pt
P = Power in W
t = time in s
 Incandescent bulbs are about 5% efficient, halogen
bulbs 15% and fluorescent 20%.
Note – Efficiency cannot ever be greater than 100%.
Ex. Problem
A 1000 W kettle takes 4 minutes to boil some water. If it
takes 1.96 x 105J of energy to heat the water, what is the
efficiency of the kettle?
P = 1000 W
t = 4 min = 240 s
Total Energy in = Pt = (1000 W)(240 s)
= 2.4 x 105 J
Energy out = 1.96 x 105 J
Efficiency = ?
Efficiency = output x 100%
Efficiency = 1.96 x 105 J x 100%
2.4 x 105 J
= 81.7%
Lesson 9: Electricity Production and the Environment
 Thermo-electric generating plants burn fossil fuels to
produce about 25% of our country’s electricity. These
fuels are considered non-renewable resources.
 However, biomass, solid material from living things,
can also be burned. Biomass is considered a renewable
energy source.
 Coal is the most common fossil fuel used in Alberta to
produce electricity. Production and use of coal has
environmental side effects.
 Open pit mining of surface deposits disturbs soil and
vegetation. Underground mines produce waste materials
called “tailings”, which accumulate near the mine.
 Burning coal produces gases such as sulfur dioxide and
carbon dioxide. SO2 is responsible for acid rain while CO2
for the greenhouse effect.
 Scrubbers spray a water solution through the waste gases,
which removes most of them but not all.
 Hydroelectric plants use water pressure to generate
electric energy. This is one of the cleanest ways to produce
 Thermonuclear plants use uranium in a process called
nuclear fission, splitting of the atom, to produce
tremendous amounts of energy (heat). However,
radioactive contamination of the environment is a real
concern with these plants.
 Another type of nuclear reaction is nuclear fusion,
joining of atoms. This occurs in the Sun and does not
produce radioactive waste. Scientists are still working on a
viable nuclear fusion reaction.
Heating the Environment
 All thermonuclear and thermo-electric-generating plants release
thermal energy (heat) into the environment.
 Thermal pollution occurs when this warm water is
retuned to the lake or river from which it is taken,
increasing the water temperature. Even a change of a few
degrees can affect the plant and animal life in the water.
Cogeneration systems produce electricity and also supply
thermal energy, such as steam and hot water, for industrial or
commercial heating. Ex. Poplar Creek plant in Ft. McMurray.
Alternative Energy Sources
 Windmills
 Solar panels
 Geothermal Energy

Report this document