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Electromagnetism
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The Motor Effect
06/05/2017
Aim:
• To use Flemming’s Left Hand Rule
• To explain how a motor works
• To construct a motor
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Fields Bar Magnets
Single Science Only
handout
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Opposite Poles
Single Science Only
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Same Poles
Single Science Only
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Fields due to Current
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Single Science Only
Single Coil of Wire
Solenoid
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Magnetic Field Lines

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There are magnetic field lines around every
 Magnet
 Electrical wire (with current flowing through it)
Anything magnetic in the field will experience a force
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Wire in a magnetic field
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The Catapult (Motor) Effect
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Motor Effect
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If a conductor carrying an electric current moves
through magnetic field lines at right angles it will
experience a force.
A charged particle will experience the same effect
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Fleming's left hand rule
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Increasing the Size of the Force
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The motor effect: true or false?
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Coil in a Magnetic Field
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How does an electric motor work?
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DC electric motor simulation
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How do we increase motor strength?
Would the same strength motor be used in both of these?
How can the strength of an electric motor be increased?
 increase the current flowing through the coil
 increase the strength of the magnet
 increase the number of turns on the coil
Worksheet
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The Motor Effect
recap
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Induction
06/05/2017
Aim:
•To observe and define induction
•To explain how electricity is generated
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Inducing current in a wire
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What is electromagnetic induction?
Current Carrying Wire + Magnetic field = Motion
Motion + Magnetic field = Current in Wire
Changing Magnetic field = Current in wire
If they are at right angles to each other
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Inducing current in a coil
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Induction
If a magnet is moved near a coil of wire a current is induced in the wire
•
Faster motion, bigger current
•
Stronger magnet, bigger current
•
More turns, bigger current
•
Change direction of motion, change direction of current
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Factors affecting induced current
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How can motion produce a current?
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What are Generators?
A generator is a device that converts mechanical energy into electrical
energy. It is the opposite of an electric motor.
Power stations use generators to produce
electricity on a large scale.
Mechanical energy is provided by rotating
turbines that can be powered by:
 high-pressure steam – in coal, oil, gas and nuclear power stations
 wind – in wind turbines
 falling water – in hydroelectric power stations
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How do AC generators work?
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AC generator simulation
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Induction: true or false?
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What is a transformer?
The voltage of an alternating current can be changed using a device
called a transformer.
A transformer contains two
coils that are wound around a
soft iron core.
iron core
The alternating current in
the primary (input) coil
produces an alternating
magnetic field.
This alternating magnetic field
induces an alternating current
in the secondary (output) coil.
primary
coil
secondary
coil
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How does a transformer change voltage?
The voltage induced in the secondary (output) coil depends on the
number of turns on the primary and secondary coils.
A step-up transformer has
more turns on the secondary
coil and so increases voltage.
A step-down transformer has
fewer turns on the secondary
coil and so decreases voltage.
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How are transformers used to supply electricity?
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Transformers

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Transformers are used to change the voltage from the Primary
(input) to the Secondary (output)
They only work with a.c. (alternating current)
Input (Primary) Voltage
=
Output (secondary) Voltage
Number of Primary Turns
Number of Secondary Turns
Example Question:

Input voltage = 230 V

Primary turns = 10000

Secondary turns = 500

What is the secondary voltage?
Worksheet
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USE ME IN THIS PRESENTATION
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http://intranet.stthomasmore.org.uk/resource/Absorb%2
0Physics/Absorb%20Physics%20for%20Alevel/Absorb%20Physics%20for%20Alevel/HTML/units/080300.html
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