Electromagnetic Induction

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CognitoElectromagnetic induction and generators

Key facts & equations

Electromagnetic induction

Moving a conductor through a magnetic field induces an EMF (electromotive force).
If circuit is complete, an induced current flows.
Faraday's law: magnitude of induced EMF proportional to rate of change of magnetic flux linkage.
Ways to induce EMF: move conductor in field, move field past conductor, rotate conductor in field.
Induced EMF is greater if: magnetic field stronger, conductor moves faster, more turns of wire.

Generators and alternators — fill in the table

Term	Detail
Generator
Alternator
Dynamo
Rotation rate

Factors affecting induced EMF — fill in the table

Factor	Effect on EMF
Stronger magnet
More turns of wire in coil
Faster rotation
Soft iron core in the coil
Coil perpendicular to field
Coil parallel to field

Lenz's law

The direction of the induced current opposes the change causing it (conservation of energy).
Moving N pole into coil: induced current creates N pole at near end → repels magnet.
This is why work must be done to move the magnet — the generator converts work to electrical energy.
Fleming's right-hand rule: used to find direction of induced current in a straight conductor.

Exam questions — 4 questions · 10 marks · AQA 8463 style

1 markHow to increase induced EMFAQA 8463 style

Which change would NOT increase the induced EMF in a generator?

A Using a stronger magnet

B Rotating the coil faster

C Using a coil with more turns

D Increasing the resistance of the external circuit

3 marksGenerator vs alternatorAQA 8463 style

Explain the difference between an alternator and a dynamo, including the type of current each produces and how this is achieved. (3 marks)

Hint: Two devices, two outputs. Key difference: how the rotating coil connects to the external circuit (slip rings vs split-ring commutator).

+30 XP

1 markZero EMF positionAQA 8463 style

When is the induced EMF in a generator coil at zero?

A When the coil is perpendicular to the magnetic field

B When the coil is parallel to the magnetic field (coil plane contains field lines)

C When the coil rotates at its maximum speed

D When more turns are added to the coil

3 marksLenz's law explanationAQA 8463 Higher style

A student pushes a bar magnet into a coil. The coil opposes the motion. Explain this observation in terms of Lenz's law and conservation of energy. (3 marks)

Hint: What Lenz's law says (oppose the change). Why the coil repels. Link to conservation of energy — otherwise energy would be created.