Motors and generators · Year 12
An electric motor uses the motor effect: forces on the sides of a current-carrying coil in a magnetic field make it spin. A generator does the reverse: spinning a coil in a field induces an alternating voltage. The same physics runs electric cars, washing machines, wind turbines and power stations.
Key facts
- Motor: electrical → kinetic energy. Generator: kinetic → electrical energy.
- A d.c. motor’s split-ring commutator reverses the coil current every half turn, keeping it spinning one way.
- A motor spins faster with more current, more turns, or a stronger field; reverse the current to reverse it.
- An alternator uses slip rings and gives a.c.; a dynamo uses a commutator and gives d.c.
- Spinning a generator faster raises both the peak e.m.f. and the frequency.
- Peak e.m.f. ε₀ = NBAω, with ω = 2πf. Frequency (Hz) = revolutions per minute ÷ 60.