Download Motors and Generators

Physics:
Motors & Generators
1
Current Carrying Conductors
1.1
Discuss the effect on the magnitude of the force on a current carrying conductor of
variations in certain properties:
 Formula:
F = Force (N)
B = Magnetic field strength (T)
I = Current (A)
F = BILsinθ
L = Length of the conductor (m)
θ = Angle of the conductor to the magnetic field




Strength of the Magnetic Field:
o Force is proportional to the strength of the magnetic field
o Stronger magnetic field, greater force on conductor
Magnitude of Current in Conductor:
o Increasing current means increasing the velocity of the electrons
o Each moving charged particle experiences a force in proportion to its velocity
Length of Conductor:
o The longer the section of conductor in a magnetic field, the more moving electrons
simultaneously experience a force
o Force is proportional to the length within the magnetic field
o Shorter length, smaller force on conductor
Angle between direction of magnetic field and conductor:
o Force is strongest when particle is moving at right angles to the magnetic field (90°)
o Force is zero when particle is moving parallel to the magnetic field (0°)
o Movement of electrons is along a length of conductor, magnitude of force varies with
angle between conductor and magnetic field
o As angle increases, force increases
Page | 1
2
Parallel Conductors
2.1
Describe qualitatively the force between long parallel current carrying conductors:
 Force between parallel conductors exists because magnetic fields due to current flowing
through the conductors interact with each other.
Direction of Force (Attraction or Repulsion):
 Depends on relative directions of the two currents
 Currents flowing in the same direction, attractive force, towards each other
 Currents flowing in opposite direction, repulsive force, away from each other
Magnitude of Force:
 Depends on magnitude of current within wire
 Increases or decreases with the product of the two currents
 Also depends on distance of separation between the conductors
 Increasing as the conductors are moved closer together
Relation to Length:
 Force between conductors depends on length of parallel conductors
 Larger for longer conductors
 "Force per unit length" - varies only with magnitude of the two currents and the distance
between them.
Formula:
F = Force (N)
F
l
k
I1I2
d
l = Length of parallel conductors (m)
I1 & I2 = Currents in the conductors (A)
d = Distance between the conductors (m)
k = constant (2.0x10-7)
Page | 2
3
Current Carrying Coils
3.1



Define torque as the turning moment of a force:
Turning force or turning moment of a force
Increased by increasing the applied force or perpendicular distance
Formula:
τ = Torque (Nm)
F = Applied force perpendicular to axis of rotation (N)
τ = Fd
d = Perpendicular distance between ‘line of action’ and pivot (m)
3.2
Describe the forces experienced by a current-carrying loop in a magnetic field and describe
the net result of the forces:
Forces on the sides ab and cd:
 Experience maximum force since the current in them is perpendicular to the magnetic field
 Magnitude of the force does not change throughout its rotation
 Using the right hand palm rule, the direction of the force on sides ab and cd can be deduced
 The net result of these two forces is to produce a torque on the loop about the axis; in the
diagram above, the torque is acting in an anticlockwise direction
Forces on the sides bc and ad:
 The sides of the loop, ad and bc, experience no force because the current is parallel to the
magnetic field
 Magnitude of the force varies from zero to maximum
o Zero when the plane of the coil is parallel to the magnetic field (i.e. as above)
o Maximum when the plane of the coil is perpendicular to the magnetic field
Net torque:
 Maximum when the plane of the coil is parallel to the magnetic field (i.e. as above)
 Direction alternates through a complete rotation
 Current-carrying loop orientated in a plane at right angles to a magnetic field will experience
no net force
Formula:
τ = nBIAcosθ
τ = Torque (Nm)
n = number of turns/loops of the coil
B = Magnetic field strength (T)
I = Current flowing through the loop (A)
A = Area of the loop (m2)
θ = Angle between the plane of the loop and the field
Page | 3
3.3
Identify that the motor effect is due to the force acting on a current carrying conductor in
a magnetic field:
Force on a Current-Carrying Conductor – The Motor Effect:
 Force on a current carrying conductor in a magnetic field causes it to move relative to the
magnetic field
 This movement caused by the forces is referred to as the Motor Effect
4
Motor Effect Applications
4.1
Describe the application of the motor effect in the galvanometer and the loudspeaker:
The Galvanometer:
 Device used to measure magnitude and direction of small DC currents
The Motor Effect:
 When current flows through the coil, the coil experiences a
force due to the presence of the external magnetic field
 The iron core of coil increases the magnitude of this force
 Needle rotated until magnetic force on the coil is equalled by
a counter-balancing ‘restraining spring’
 Scale of galvanometer is linear, amount of deflection
proportional to current flowing through coil
The Loudspeaker:
 Device that transforms electrical energy into sound energy
The Motor Effect:
 A current-carrying coil interacting with a permanent magnet
experiences a force as a result of the motor effect
 This force causes the coil to vibrate rapidly back-and-forth, in turn
making the speaker cone vibrate and send sound waves into the air
 When the magnitude of the current increases, so too does the
force on the coil
 When the force on the coil increases, it moves more and the
produced sound is louder
Page | 4
5
DC Electric Motors
An electric motor is a device which converts electrical energy to useful mechanical energy (usually
rotation)
5.1
Describe the main features of a DC electric motor and the role of each feature & identify
that the required magnetic fields can be produced either by current-carrying coils or permanent
magnets:
External Magnets:
1. Permanent Magnets:
 Made of ferromagnetic metals – two permanent magnets curved around the armature on
opposite sides of the motor, opposite poles face each other
 Role: Supplies the magnetic field producing the motor effect
2. Electromagnetic coils:
 A coil of current-carrying wire wound around a soft iron core – coils are shaped to fit around
the armature
 Role: Provides a stronger magnetic field which can be switched on and off when required
Armature:
 Cylinder of laminated iron mounted on an axle which coils are wound onto and placed inside
the magnetic field
 Role: Maximises the torque that can act on the coils, thus making the motor run more
efficiently – laminations reduce eddy currents which might otherwise overheat the armature
Rotor Coils:
 Turns of wire wound onto the armature – the ends of the coils are connected to bars on the
commutator
 Role: Provides the torque as the current passing through the coils interacts with the
magnetic field. Any torque acting on the coils is transferred to the rotor (which the coils are
mounted on) and hence to the axle
Split-ring commutator:
 Cylindrical ring of metal mounted on the axle at one end of the armature – cut into an even
number of separate bars in which each opposite pair of bars is connected to one coil
 Role: Reverses the direction of current flow every half-revolution of the motor to ensure
that the torque on each coil is always in the same direction
Brushes:
 Compressed carbon blocks, connected to an external circuit, mounted on opposite sides of
the commutator – spring loaded to make close contact with the commutator bars
 Role: Provides the contact to conduct current into and out of the coils – they are also
responsible for maximising the torque on the axle
Axle:
 Cylindrical bar of hardened steel, through the centre of the armature and commutator
 Role: Provides a centre of rotation for the motor. Useful work extracted from the motor via
a pulley or cog mounted on the axle
Page | 5
6
Michael Faraday
6.1
Outline Michael Faraday's discovery of the generation of an electric current by a moving
magnet:
After discovering that an electric current produces a magnetic field, in 1820, Faraday’s ideas about
conservation of energy led him to believe that since an electric current could cause a magnetic field,
a moving magnetic field should be able to produce an electric current.
In 1831, Faraday attached two wires through a sliding contact to touch a rotating copper disk
located between the poles of a horseshoe magnet. This induced a direct current and was the basis
to an electric generator.
Faradays explanation was that the electric current was induced in the moving disk as it cut a
number of lines of magnetic force coming from the magnet (the magnetic field). The wires allowed
the current to flow in an external circuit where it could be detected.
7
Magnetic Flux
7.1 Define magnetic field strength (B) as magnetic flux density:
Representing Magnetic Fields:
 Magnetic flux lines 'flowing' out of the north pole and into the south pole
 Lines closer together near the poles where magnetic field is strongest
 Lines further apart at greater distances from the magnet
 Magnetic field of stronger magnet, larger number of magnetic flux lines
 Magnetic field of weaker magnet, smaller number of magnetic flux lines
Magnetic Flux Density:
 Measure of the number of magnetic flux lines passing through a unit area (1m2)
 Magnetic field strength at a point is the same as the magnetic flux density at that point
7.2
Describe the concept of magnetic flux in terms of magnetic flux density and area:
Magnetic Flux:
 Amount of magnetic field lines passing through a given area
 Product of strength of magnetic field (magnetic flux density) and area of coil perpendicular
to magnetic field
 Represented diagrammatically as number of flux lines passing through the area
 The relationship of the magnetic flux is given by (Note: This formula is not required):
Φ = BA
where Φ = the total magnetic flux (Wb)
B = magnetic field strength (T)
A = perpendicular area through which the flux passes (m2)
Page | 6
7.3
Describe generated potential difference as the rate of change of magnetic flux through a
circuit:
Faraday's Law of Electromagnetic Induction:
 The size of an induced EMF is directly proportional to the rate of change in magnetic flux
 In order to induce an EMF, a changing magnetic flux is essential
Factors that determine the size of the induced EMF:
 The size of the change in the magnetic field
 The speed of the relative motion between the magnetic field and the conductor
 The number of turns of coil or conductors
 The change in area that the magnetic field passes through
 Formula (Note: This formula is not required):
ɛ=n
ΔΦ
Δt
where ɛ = Potential difference (V)
n = Number of turns in the coil
Φ = Magnetic flux (Wb)
t = Time (seconds)
ΔΦ
Δt
8
= Rate of change in magnetic flux
Lenz’s Law
8.1
Account for Lenz's Law in terms of conservation of energy and relate it to the production
of back EMF in motors & explain that in electric motors, back EMF opposes the supply EMF:
Lenz’s Law:
 “The direction of any induced EMF will always be such that it opposes the change that
caused it”
 To find the direction of an induced emf (or induced current) we apply the RHPR to the given
situation and then reverse the direction of the current flow
Conservation of Energy:
 The law of conservation of energy states: Energy cannot be created or destroyed, it can only
be transformed or transferred
Consider a magnet moving into a coil:
 By Lenz's law, work must be done to move magnet into coil providing energy to induce EMF
 If Lenz's Law did not hold true, the magnet would be accelerated into the coil – i.e. creating
mechanical energy with no input energy
 Thus, to obey the law of conservation of energy, the induced current must flow to oppose
the cause
Back EMF:
 When an electric motor is first switched on, the applied voltage produces a large current in
the coils. When the coils begin to rotate, changing flux within coils induces an emf; by Lenz's
law, the induced emf is opposite to the emf applied to the motor and this is known as the
back emf
Page | 7
8.2



9
Explain the production of eddy currents in terms of Lenz's Law:
Eddy currents - current loops induced in a conductor by a changing magnetic field
By Lenz's Law, eddy currents oppose the changing magnetic field producing them
Eddy currents produce its own magnetic field which opposes the relative motion of the
magnetic field which created it
Applications of Induction
9.1





9.2



Identify how eddy currents have been utilised in electromagnetic braking:
Eddy current braking works when a rotating metal disc is placed within a magnetic field,
causing the motion to slow down
This occurs because eddy currents are induced in the metal disc as a result of the presence
of a magnetic field, thus changing magnetic flux
The eddy currents circulate to create a magnetic field which opposes the motion of the disc,
hence slowing it down
As the motion of the metal disc decreases, so does the effect of the braking due to weaker
eddy currents being induced, resulting in a smooth stopping motion
Eddy current braking has been used for train braking and also some roller-coasters where
the cart needs to stop at the end of the track
o Very strong magnets are lowered down next to the metal wheels, inducing eddy
currents. The eddy currents oppose the motion of the wheels, therefore the slowing
down the motion of the train
Explain how induction is used in cook tops in electric ranges:
In order for induction to occur there needs to be a change in magnetic flux, therefore
induction cook tops work on AC current, to create a fluctuating magnetic field
When an iron-rich (ferromagnetic) cookware item is placed on the induction cooktop's
cooking element, eddy currents are induced within the cookware at its base
With the high frequency, it causes the eddy currents to move around the cookware very
fast, and since iron is a relatively poor conductor of electricity, the resistance in the
cookware causes heat to be produced within the cookware, effectively heating/cooking its
contents.
Page | 8
10
Generators
An electric generator is one that converts mechanical energy to electrical energy using the principle
of electromagnetic induction.
10.1






Describe the main components of a generator:
Rotor: Usually consists of several coils wound on an armature which is made to rotate
within a magnetic field.
Armature: Cylinder of laminated iron mounted on an axle which is carried in bearings
mounted in the external structure. Torque applied to axle to make the rotor spin.
Coil: Each coil consists of many turns of copper wire wound on the armature. The two ends
of each coil are connected either to two slip rings (AC Generator) or two opposite bars of a
split-ring commutator (DC Generator).
Brushes: The brushes are carbon blocks that maintain contact with the ends of the coils via
the slip rings (AC) or the split-ring commutator (DC), and conduct electric current from the
coils to the external circuit.
Stator: Fixed part of the generator which supplies the magnetic field in which the coils
rotate.
Magnetic field: The magnetic field can be provided by permanent magnets or
electromagnets which are mounted and shaped in such a way that opposite poles face each
other and wrap around the rotor.
10.2 Compare the structure and function of a generator to an electric motor:
Structure:
Similarities:
 Both have a stator providing the magnetic field, both have a rotor which rotates in this field
 In both, the magnetic field is supplied by either permanent magnets or electromagnets
 In both, rotor consists of coils wound on armature connected to brushes
Differences:
 DC Generators and electric motors – use a split-ring commutator to connect external circuit
 AC Generators – use slip rings to connect external circuit
Function:
 The function of an electric motor is the reverse function of a generator
Electric motors:
 Converts electrical energy into mechanical energy
 Rotates when current is supplied
Generators:
 Converts mechanical energy into electrical energy
 Supplies current when rotor rotates
Page | 9
11
AC vs. DC Generators
11.1 Describe the differences between AC and DC generators & discuss advantages /
disadvantages of AC and DC generators related to their use:
AC Generators:
 Brushes run on slip rings, constant connection between
coil and external circuit
 Induced EMF changes polarity with every half-turn of
the coil
 Voltage in the external circuit varies like a sine wave
 Current alternates direction
EMF Output of an AC Generator
Advantages:
 Brushes in AC generator last longer because they don't wear as quickly
 Less maintenance and more reliable, better suited to high current demands
 Uses slip rings which cost less to manufacture and requires less maintenance
 AC voltage can be easily increased/decreased using transformers
 Can be used for power distribution
 AC output loses less energy during transmission than DC output
Disadvantages:
 Cannot be used to power some devices which rely solely on DC current to function
 AC output in different regions around the country must be synchronised for correct
integration of electricity – i.e. have the same frequency and are in-phase
 AC output is much more dangerous than the equivalent DC output
DC Generators:
 Brushes run on split-ring commutator, which work
by reversing the connection between the coil and
the external circuit each half-turn
 Induced emf does not change polarity
 Voltage in external circuit fluctuates between zero
and maximum
 Current flows in one constant direction
EMF Output of a DC Generator
Advantages:
 DC output can be used for devices which rely solely on DC current to function
 DC current is generally more powerful than AC (for a given voltage)
Disadvantages:
 Brushes in DC generator do not last as long because they wear quicker
 Chance of creating electrical short circuit between segments due to pieces of metal worn
from commutator bars
 Cannot supply power over long distance
Page | 10
12
Edison vs. Westinghouse
12.1 Analyse the competition between Westinghouse and Edison to supply electricity to cities:
Westinghouse was the overall winner, as the AC system was more efficient.
Thomas Edison:
 Direct Current System
 DC Generators use commutators, which were a problem – i.e. maintenance, cost, performs
poorly at high speed rotations
 Could only supply power to areas a few kilometres away
 Relied on thick copper cables to carry electric current
George Westinghouse:
 Alternating Current System
 Westinghouse saw the advantages of AC, and so he purchased the rights to Tesla's AC
motors and generators
 AC transmissions through the action of transformers were much more energy efficient
 Electricity could be transmitted over longer distances with only a small energy loss
13
Transmission Lines
13.1 Identify how transmission lines are insulated from supporting structures and protected
from lightning strikes:
Insulation from Supporting Structures:
 Large insulators that consist of stacks of disks made from porcelain are used to separate
transmission lines from metal support towers
 Prevents sparks jumping across the gap between the wires and tower
 The insulators (commonly porcelain) are strong and retains its high insulating properties
even under a very high voltage
Protection from Lightning Strikes:
 A non-current carrying wire runs over and parallel to the transmission wires.
 If lightning strikes it will hit the overhead wire first and the wire will conduct the huge
current of the lightning into the earth, leaving the transmission wires untouched
 The transmission lines do not suffer a sudden surge of voltage
Page | 11
14
Energy Losses
14.1 Discuss the energy losses that occur as energy is fed through transmission lines from the
generator to the consumer:
Energy loss due to resistance:
 As current flows through the transmission lines that has a resistance, heat will be dissipated
 The heat lost during transmission can be quantitatively described by using the formula:
 Formula:
P = I 2R
where P = heat lost during transmission (J)
I = the current flow through the wire (A)
R = the total resistance of the wire (Ω)
(This equation can be derived by combining the
power equation P = IV and Ohm’s law V = IR)
Minimisation:
 Transmission at highest possible voltage, lowest possible current
 Careful choice of materials – i.e. using good conductors (e.g. copper), thicker wires = less resistance
Energy loss due to induction of eddy currents:
 Induction of eddy currents in iron core of transformers
 Circulation of eddy currents generates heat representing energy loss to the system
Minimisation:
 Transformer core made of laminated iron - thin layers of iron, separated by thin insulating layers
 Limiting eddy currents and reducing corresponding heat loss by utilising cooling fins on the outside of
the transformer and cooling oil circulating on the inside
Page | 12
15
Impact of AC Generators
15.1 Assess the effects of the development of AC generators on society and the environment:
Effects on society:
Positive Effects:
 Development of a wide range of machines, processes and appliances – improving the
standard of living
 Many tasks once performed by hand now can be accomplished with electrical appliances
 Most domestic and industrial work requires less labour
 Influencing technology development - tasks such as electronic communication now achieved
Negative Effects:
 Reduction in demand for unskilled labour, thus increasing long-term unemployment
 Disruption to supply compromises safety, causes widespread inconvenience and loss of
production
 Injuries and deaths from electric shocks with the widespread use of AC power
 A major electricity failure could cause economic crisis
Effects on Environment:
Negative Effects:
 Transmission lines criss-cross the country, strip through environmentally sensitive areas
 Remote wilderness areas tapped for energy resources such as hydroelectricity
 Air pollution from burning fossil fuels, cause of acid rain
 Global increase of atmospheric C02, long-term global climate change
 Radioactive waste from nuclear power stations
16
Impact of Transformers
16.1

Discuss the impact of the development of transformers on society:
More efficient transmission of electricity – power loss during transmission is dramatically
reduced
Allows the development of devices which run at different voltages
Access to high-voltage electricity in remote areas, stepped-down by transformers in order
for use in devices
Raised living standards in rural communities (e.g. electrical lighting, refrigeration, air-con.)
Industry no longer clustered around power stations and can be developed away from
residential areas
Power stations in remote locations, relocated pollution away from homes





Page | 13
16.2 Discuss the need for transformers in the transfer of electrical energy from a power station
to its point of use & explain the role of transformers in electricity sub-stations:
 Without transformers electricity would be generated at voltage typically used, resulting in
very large energy losses and costly transmission losses
 In large cities, many power stations would be required every few kilometres and each
different voltages require separate power stations and distribution systems
Transformers:
 More efficient to use very high voltages for long distance transmission
 Transformers step-up voltage for transmission, progressively step-down voltage along
transmission lines until it reaches consumer
The voltage change during the transmission from the power plant to consumers:
Electricity is usually generated by a three-phase AC generator; generally the voltage generated is as big
as 23000V and current output from each set of the coil is almost 10000A
For long distance transmissions, the electricity is then fed into a step-up transformer that increases the
voltage to 330000V and correspondingly decreases the size of the current (P=VI)
After this electricity has been transmitted over a long distance, the voltage is stepped down at different
regional sub-stations, mainly for safety reasons. Correspondingly, the current increases.
Eventually, the voltage is stepped-down to 240V at the local telegraph pole transformers for domestic
uses; industries may use slightly higher voltages
17
Transformers
17.1

Describe the purpose of transformers in electric circuits:
Transformers are devices that increase or decrease the size of the AC voltage as it passes
through them via electromagnetic induction
Step-down transformers are used for appliances containing components requiring lower
voltages – e.g. clock radios, hair dryers, CD players, etc.
Step-up transformers are used for appliances which require higher voltages to function –
e.g. televisions, air conditioners, etc.
Many appliances contain both step-up and step-down transformers supplying different
voltages for different components



Page | 14
17.2 Compare step-up and step-down transformers:
Step-up transformers:
 Two inductively coupled coils on laminated iron core
 The secondary coil has more turns than the primary coil
 Voltage output from the secondary coil is larger than the voltage input into the primary coil
 Lower output current than input current
 Used for:
o Increasing voltage at power stations for transmission
o Devices: televisions, air conditioners, etc.
Step-down transformers:
 Two inductively coupled coils on laminated iron core
 The secondary coil has less turns than the primary coil
 Lower output voltage than input voltage
 Higher output current than input current
 Used for:
o Decreasing voltage at sub-stations for domestic and commercial use
o Devices: clock radios, hair dryers, CD players, etc.
18
Voltages and Coils
18.1 Identify the relationship between the ratio of the number of coils in the primary and
secondary coils and the ratio of primary to secondary voltage:
 Ratio of primary to secondary voltage = ratio of number of turns in the coils
 Step-up transformers - more turns and higher voltage in secondary coil
 Step-down transformers - less turns and lower voltage in secondary coil
Formula:
where Vp = voltage input into primary coil (V)
Vp
Vs
np
ns
Vs = voltage output from secondary coil (V)
np = number of turns of the primary coil
ns = number of turns of the secondary coil
18.2 Explain why voltage transformations are related to conservation of energy:
Conservation of Energy:
 Amount of electrical energy entering must equal total energy in all forms leaving
 Power in = power out
Ideal transformers:
 Pp = IpVp = IsVs = Ps
where subscript ‘p’ indicates primary coil and subscript ‘s’ indicates secondary coil
 No power loss – if voltage increases, current correspondingly decreases, and vice versa
Real transformers:
 Heat due to eddy currents acting in the resistance of iron core
 Energy is lost from the system in the form of heat – escaping into the air
 Power output cannot exceed power input, power output is less than power input;
Pinitial > Pfinal due to loss of heat energy
Page | 15
19
Electrical appliances in the home
19.1 Discuss why some electrical appliances in the home that are connected to the mains
domestic power supply use a transformer:
Many household appliances function at voltages other than the standard domestic voltage of 240V
Appliances that run on 240V AC:
 Electricity supplied to homes typically 240 V AC
 Many domestic appliances designed to run at this voltage
 Connected directly to the mains supply without a transformer
Running on Lower Voltages:
 Some appliances contain components operating at lower voltages than supplied
 For these appliances, a step-down transformer can be used to decrease the voltage to
required – e.g. phone chargers use a transformer to step-down the voltage from 240V to the
required voltage (commonly <10V)
Running on Higher Voltages:
 Appliances such as television receivers and computer monitors contain cathode ray tubes
requiring voltages above supply voltage
 These appliances have a built-in step-up transformer to provide the necessary voltage
20
Heat Reduction
20.1 Discuss how difficulties of heating caused by eddy currents in transformers may be
overcome:
Reducing Eddy Currents:
 To minimise the heat dissipation by the soft iron core, the core is laminated – stacks of thin
iron sheets, each coated with insulation materials
 Lamination effectively increases the resistance of the core to the flow of eddy currents,
therefore restricting the circulation of large eddy currents – thus, less heat dissipation
Keeping Transformers Cool:
 Ventilated cases to allow air to remove heat by convection
 Internal fan to assist air circulation to remove excess heat faster
 Transformer case filled with a non-conducting oil which circulates inside the case; transports
heat produced in core to outside where heat can be dissipated to environment
 Heat-sink fins added to metal transformer case, heat dissipation can occur more quickly over
larger surface area
 Large transformers such as at sub-stations located in well-ventilated areas to maximise air
flow around them for cooling
Page | 16
21
AC Electric Motors
21.1 Describe the main features of an AC electric motor:
Standard AC Electric Motors:
 Same features as DC electric motor, except slip rings used instead of split-ring commutator
 Slip rings – conducts electricity from the power source without interfering with the rotation
of the coil
 The motor spins at 50 revolutions per second, as it is the same frequency as the oscillation of
AC current (50Hz)
AC Induction Motors:
 Stator:
The stationary component of the motor, it contains the electromagnet coils which create the
magnetic field and it surrounds the rotor.
o Electromagnet coils: When current flows through the coils, it produces a magnetic
field. There are 3 pairs of coils in the stator, which when turned on one after the
other, creates a rotating magnetic field.
 Rotor:
The rotating component of the motor. Induced eddy currents flow in the rotor in such a way
that it will rotate in the same direction as the rotating magnetic field created by the stator.
o Squirrel cage: The squirrel cage is made up of parallel aluminium bars that have their
ends embedded in a metal ring at each terminal. It is covered by laminated soft iron
and embedded in the stator.
22
Energy Transformations
22.1 Gather, process and analyse information to identify some of the energy transfers and
transformations involving the conversion of electrical energy into more useful forms in the home
and industry
 In the home:
o Ovens and kettles create heat energy from electrical energy
o Stereo systems create sound energy from electrical energy
o Light globes and TVs create light energy from electrical energy
o Washing machines create kinetic energy from electrical energy
 In the industry:
o Mainly turning electrical energy into kinetic energy for drills and other machinery
o Light energy in large industrial lights from electrical energy
Page | 17
Practicals to cover:
(1.) Perform a first-hand investigation to demonstrate the motor effect
(2.) Perform an investigation to model the generation of an electric current by moving a magnet
in a coil or a coil near a magnet
(2.) Plan, choose equipment or resources for, and perform a first-hand investigation to predict
and verify the effect on a generated electric current when the distance between the coil and
magnet is varied, the strength of the magnet is varied, the relative motion between the coil and
the magnet is varied
(3.) Plan, choose equipment or resources for, and perform a first-hand investigation to
demonstrate the production of an alternating current
(4.) Perform an investigation to model the structure of a transformer to demonstrate how
secondary voltage is produced
(5.) Perform an investigation to demonstrate the principle of an AC induction motor
Page | 18