What are the Electric Generators?

An electric generator is a situation in which a loop of conducting wire rotates in an area with a magnetic field. During the first half of the cycle, a positive magnetic field drives a clockwise current in the loop, and during the second half of the cycle, a now negative magnetic field generates a counterclockwise current. (If you are having trouble picturing this, pretend that you are an observer belted to the conductor.) The name "alternating current" (AC) is given to the current generated this way.

In the first half of the cycle, the current builds and falls in the positive direction, and in the second half of the cycle, the current builds up and weakens in the negative direction. If the loop is rotated at a steady pace, the current provided looks like a sine curve. A generator turns the mechanical energy of the loop of wire rotating into AC electric current.
 
Batteries supply direct current (DC), a current which is roughly constant and in one direction only. A generator with a split ring can approximate a battery.