Q 12-07-128JEE MainJEE Main 2021 (25 Jul, Shift 2)Medium
A $10\ \Omega$ resistance is connected across $220$ V $-$ $50$ Hz AC supply. The time taken by the current to change from its maximum value to the rms value is:
Answer: (A) $2.5$ ms
$i = i_0\sin\omega t$. Maximum at $\omega t = \dfrac{\pi}{2}$; next equal to $\dfrac{i_0}{\sqrt{2}}$ at $\omega t = \dfrac{3\pi}{4}$.
$\Delta t = \dfrac{\pi/4}{\omega} = \dfrac{T}{8} = \dfrac{20\ \text{ms}}{8} = 2.5$ ms.
Solution by Sreeraj P, M.Sc Physics