$(a)$ Write three differences between $AC$ and $DC$.
$(b)$ State the frequency of $AC$ supply in India and mention the potential difference between the neutral and live wire in a domestic circuit.
How many times does $AC$ change its direction in one second?

(N/A) Differences between $AC$ and $DC$:
| Feature | $AC$ | $DC$ |
| :--- | :--- | :--- |
| $(i)$ Transmission | Can be transmitted over long distances effectively. | Cannot be transmitted over long distances effectively. |
| $(ii)$ Direction | Changes its direction at regular intervals of time. | Does not change its direction. |
| $(iii)$ Representation | Represented by a sinusoidal wave. | Represented by a straight line parallel to the time axis. |
$(b)$
- The frequency of $AC$ supply in India is $50 \, Hz$.
- The potential difference between the neutral and live wire in a domestic circuit is $220 \, V$ to $240 \, V$ (standard is $220 \, V$).
- Since the frequency is $50 \, Hz$,the current completes $50$ cycles per second. In each cycle,the current changes direction twice. Therefore,the $AC$ changes its direction $50 \times 2 = 100$ times in one second.