In which of the following cases e.m.f. is induced?

(i) A current is started in a wire held near a loop of wire.

(ii) The current is switched off in a wire held near a loop of wire.

(iii) A magnet is moved through a loop of wire.

(iv) A loop of wire is held near a magnet.

What determines the frequency of a.c. produced in a generator?

What energy conversion does take place in a generator when it is in use?

State one advantage of using an a.c. over the d.c.