Explanation

(b) An alternating current is one whose magnitude changes continuously with time between zero and a maximum value and whose direction reverses periodically. The relation between frequency ($f$) and time ($T$) is.
[image:7_image51.png]
$T = \frac{1}{f} = \frac{1}{50} = 0.02\ s$
As is clear from the figure time taken to reach the maximum value is
$\frac{T}{4} = \frac{0.02}{4} = 0.005\ s$