Generators transfer mechanical energy into electrical energy through electromagnetic induction. An alternator uses a rotating coil and slip rings to produce ac; the output p.d. changes sign each half-turn. A dynamo uses a split-ring arrangement to produce a unidirectional, usually varying output. Faster rotation can increase output frequency and maximum p.d. Example: State a dynamo’s output direction. Unidirectional, though its size can vary. Use clear labels. State assumptions. Apply the model.