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REVISION NOTES: PHYSICS 3
ELECTROMAGNETISM



The Motor Effect

When a current is passed along a wire in a magnetic field, a force may be exerted on the wire. This
is the motor effect.






There is always force acting on the wire unless the wire is parallel to the magnetic fields.…

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REVISION NOTES: PHYSICS 3
ELECTROMAGNETISM





Electromagnetic Induction

Hospitals have emergency electricity generators in case the mains fail. A generator contains coils of
wire which spin in a magnetic field. A potential difference (or voltage) is created (or induced) in
the wire when it cuts across field lines. If the wire…

Page 3

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REVISION NOTES: PHYSICS 3
ELECTROMAGNETISM





The coil is connected to an ammeter via the metal brushes attached to the commutator rings. When
the coil turns steadily in one direction, the meter pointer deflects one way first, then the opposite
way, and then back again. This carries on as long as…

Page 4

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REVISION NOTES: PHYSICS 3
ELECTROMAGNETISM






Transformers

Electricity reaches our homes from a power station via a network of cables called the National
Grid. A transformer is used at each stage to change the alternating voltage. A transformer consists
of two coils of insulated wire, both wound round the same iron…

Page 5

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REVISION NOTES: PHYSICS 3
ELECTROMAGNETISM





The National Grid

Electricity is supplied to our homes via the National Grid. The higher the potential difference, the
greater the efficiency of transferring the electrical power through the grid. This is why we use:

stepup transformers to take the p.d. from a power station…

Page 6

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REVISION NOTES: PHYSICS 3
ELECTROMAGNETISM





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