The main difference between alternating current and direct current is that in the AC the direction of current reverses periodically, whereas in DC the direction of current is constant. AC varies in magnitude continuously whereas magnitude of DC remains same. AC can be transmitted over long distance without much loss of energy but when DC is transmitted over long distance there is much loss of energy.

In India, the frequency of AC is 50 Hz. In each cycle the current alters its direction twice. Thus AC changes direction 2 x 50 = 100 times in one second.