Question

A resistance of $20\Omega$ is connected to a source of alternating current rated $110V,50Hz$. Then the time taken by the current to changes from its maximum value to the r.m.s. value is

• A. $2.5\times {10}^{-3}sec$
• B. $2.5\times {10}^{-5}sec$
• C. $5\times {10}^{-3}sec$
• D. $2.5\times {10}^{-4}sec$

Answer 1

The correct option is A $2.5\times {10}^{-3}sec$

We know that

$i=i_{0}cos2\pi ft$

$i=i_o/\sqrt{2}$

on comparing, time taken to move maximum value to r.m.s value

$t=\frac{1}{8f}$

$t=\frac{1}{8\times 50}$

$t=2.5\times {10}^{-3}sec$