Name and state the principle of a simple a.c. generator. What is it's use?

In an a.c generator the speed at which the coil rotates is doubled. How would this affect (a) the frequency of output voltage (b) the maximum output voltage.

State (i) two dis-similarities, and (ii) two similarities between a d.c. motor and an a.c. generator.

For what purpose are the transformers used? On which type of current do transformers work?