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Electromagnetic Induction
A magnetic field can be used to produce
When the wire is moved across the
magnetic field a small EMF(voltage) is
created. This is called electromagnetic
“EMF is induced”
Induced EMF increased by:
-Moving wire faster
-Using stronger magnet
-Increasing length of wire.
Induced Currents
Fleming’s right hand rule:
The current and EMF
direction can be reversed
• moving the wire in the
opposite direction
• turning the magnet
round so that the field
direction reversed.
Difference between the left hand and the right hand
-When current causes motion the left hand rule
How is Current Induced in
a Coil of Wire?
When a magnet is moved towards (or inside)
a coil of wire, a current is induced inside
the wire. This can be shown by connecting
the coil to a very sensitive ammeter called
a galvanometer.
The size of the induced current can be made bigger by:
1. Using a stronger magnet.
2. Moving the magnet at a faster speed.
3. Using more turns of wire on the coil.
These all result in the pointer on the galvanometer
moving further to the right.
The direction of the current can be reversed by:
1. Moving the magnet in the opposite direction.
2. Using a magnet facing the opposite way round
(with North becoming South).
These both result in the pointer on the galvanometer
moving to the left.
If the magnet stops moving, even though it may still be
inside the coil of wire, no current is induced in the wire.
The coil rotates
Magnetic fields are cut
EMF is generated
Causes current to flow
Coil rotates– upwards,
downwards, upwards Increasing EMF:
causing the current to - Increasing the number of
turns on coil
flow backwards,
forwards, backwards. - Increasing area of coil
- Use stronger magnet
- Rotate coil faster
Coils and Transformers
Moving magnet induces EMF
Magnetic field SAME effect.
Mutual induction: when coils are magnetically
linked so that changing current in one coil
causes an induced EMF in the other.
Simple Transformer
output voltage
Input voltage
Turns in output coil
Turns on input coil
Alternating current
flows through primary
This sets up an altering
magnetic field in the
Coils of the secondary
coil ‘cut’ the altering
magnetic field thus
inducing an alternating
voltage in the output
Step-up and Step-down
Step-up: this is when the
number of output coils is
greater than the number
of input coils which
means that there will be
a greater output voltage
as opposed to input
Step-down: this is when the
number of output coils is less
than the number of input coils
which means that there will be
less output voltage as opposed
to input voltage.
Power Through a Transformer
Input x Input = Output x Output
voltage current voltage current
Magnetic Effects of Current
When an electric current is passed through a
wire an magnetic field is produced. The
features of this magnetic field are:
 They
are circles
 Field is strongest close to the wire
 Increasing current  increases strength of field.
Right-hand grip rule
These are types of magnets that can be
switched on and off.
Iron core
The strength of the magnetic field can be increased by:
- Increasing the current.
- Increasing the number of turns in the coil
Magnetic Relay
When electricity is passed through the coil end
wires, it induced a magnetic field in the iron
ROD. This attracts the iron STRIP causing both
metal contacts to touch.
Circuit Breaker
Circuit breaker- it is an
automatic switch cutting
off the current within a
circuit if it rises above a
specified value.
In the case on the left, the
pull of the electromagnet
has become so strong that
it has attracted the soft iron
armature. This causes the
contacts to open and stop
the current.
- If u press the reset button,
the contacts close once
Magnetic force on the current
Copper is a non-magnet
 feels no force of the
 If it has a current
passing through it, there
will obviously be a force
on the wire.
The wire moves ACROSS
the field. It is not
attracted to it.
Force is increased if:
-Current is increased
-Stronger magnet is used
-Length of wire in field is
Flemings Left Hand Rule
An electric motor transfers electrical energy to
kinetic energy.
A motor is made up from a coil
of wire which is positioned
between the two poles of the
When the current flows through
the coil, it creates a magnetic
field. This magnetic field that is
produced interacts with the
magnetic field produced by the
2 permanent magnets.
The combination of these two
magnetic fields exert a force,
pushing the wire at right angles
Improve turning
Increasing Turning Effect
Increase the current
Use a stronger magnet
Increase the number of turns on the coil
Increase the area of the coil.
Reversing the rotation
can be done by:
• reversing the battery
• reversing poles