15 ELECTROMAGNETIC MACHINESMagnetic field patterns

• Investigate patterns of magnetic fields lines around magnets, wires and coils

Faraday’s law

• Investigate the laws of electromagnetic induction

Transformer design

• Review principles of transformer operation

• Explain optimisation of transformer design in the context of magnetic circuits

Eddy currents and Lenz’s law

• Observe and explain the effects of eddy currents in terms of Lenz’s law

Dynamos and generators

• Explain the operation of dynamos and generators in terms of laws of electromagnetic induction

• Learn how generator design is optimised for maximum output

The catapult effect

• Observe and explain the forces on a current-carrying wire in a magnetic field

• Explain how this effect is used in d.c. electric motors

Building electric motors

• Build and test a simple d.c. Motor

• Compare advantages and disadvantages of d.c. motors versus induction motors

Generators and motors compared

• Learn about similarities between them

• Explain operation under loads

• Derive the relationF = I l B

Starter: Electromagnetism revision

Generate questions from these answers:• The product of the flux multiplied by the number of turns.• Rate of change of flux linkage.• Because the direction of the EMF opposes the change producing it.• To minimise energy losses due to eddy currents.• Measure the gradient of the graph of flux against time.• As short and fat as possible.• As short and straight as possible.• In phase with the alternating current.• 90o out of phase with the flux.• Because eddy currents circulate in the rotor, generating their own

magnetic fields which interact with the rotating flux.• As small an air gap as possible.