Frequency refers to how many times the current or voltage alternates (or cycles) in a second. It is measured in Hertz (Hz), where 1 Hz equals one cycle per second.

In an Alternating current (AC) system, the current flows back and forth, constantly changing direction. The frequency tells us how many times this change happens each second.

The frequency of a.c. in our country is 50 Hz means that the current reverses its direction 50 times per second. So, for every second, the AC voltage completes 50 cycles of moving in one direction and then reversing back in the other.