Observe the following diagram and answer the questions given below :[Figure: a coil ABCD placed between the poles N and S of a magnet, its ends connected to two conducting rings R1 and R2 on an axle; carbon brushes B1 and B2 press against the rings a…

Answer: (a) A.C. electric generator (dynamo); (b) electromagnetic induction; (d) to generate electricity.

(a) The figure shows a coil rotating between the poles of a magnet with its ends joined to two slip rings and carbon brushes — an A.C. generator.

(b) It works on the principle of electromagnetic induction: when the magnetic flux linked with a coil changes, an e.m.f. is induced in the coil (Faraday’s law).

(c) When the coil ABCD is rotated in the magnetic field, the magnetic flux linked with it keeps changing continuously, so an induced e.m.f. and current are set up in it. In one half rotation the current flows in one direction (A→B→C→D) and in the next half rotation it reverses, because the sides AB and CD exchange their positions in the field. The current taken out through the slip rings and brushes is therefore alternating, changing direction after every half rotation.

(d) It converts mechanical energy into electrical energy and is used to generate electricity in power stations (hydroelectric, thermal and nuclear plants all use generators).