Paper 3 Alternating Current Generators Answers

Q1 Generator Design

1. Output frequency increases by $50\%$ because it follows rotation frequency. [1]
2. ${\mathcal{E}}_0\propto N\omega$, so factor $=2\times 1.5=3.0$. [2]
3. Mechanical work turns the coil against electromagnetic opposition; energy is transferred to electrical energy in the circuit and then dissipated/usefully used in the load. [3]

Q2 Quarter-Turn Map

1. Flux linkage varies sinusoidally: maximum positive, zero, maximum negative, zero, then repeats. [3]
2. $\mathcal{E}=-d(N\Phi )/dt$, so the emf sign is opposite to the gradient sign by Lenz/Faraday convention. [3]
3. Larger current in the magnetic field produces a larger opposing torque, so more mechanical input power is required. [2]