An alternating electric current has a frequency of $50 \, Hz$. How many times does it change its direction in one second? Give reason for your answer.

(100) The current changes its direction $100$ times in one second.
Reason: $A$ frequency of $50 \, Hz$ means that the alternating current completes $50$ cycles in one second.
In each cycle,the current changes its direction twice (once in the positive half-cycle and once in the negative half-cycle).
Therefore,the total number of direction changes in one second is $50 \times 2 = 100$ times.