What is the difference between a direct current and an alternating current?

What is the difference between a direct current and an alternating current? How many times does AC used in India change direction in one second?

Answer:
Direct current always flows in one direction but the alternating current reverses its direction periodically. Also the magnitude of current in case of DC is same throughout whereas in case of AC, it changes continuously. The frequency of AC in India is 50 Hz and in each cycle it alters direction twice. Therefore, AC changes direction 2 X 50 =100 times in one second.