Q 12-01-122JEE MainJEE Main 2021 (26 Aug, Shift 1)Medium
A solid metal sphere of radius $R$ having charge $q$ is enclosed inside the concentric spherical shell of inner radius $a$ and outer radius $b$ as shown in the figure. The approximate variation of electric field $\vec{E}$, as a function of distance $r$, from centre $O$, is given by:
Answer: (C) see figure
- $r < R$: inside the conducting sphere, $E = 0$.
- $R < r < a$: $E = \dfrac{kq}{r^2}$, decreasing.
- $a < r < b$: inside the conducting shell, $E = 0$ (charge $-q$ is induced on its inner surface).
- $r > b$: $+q$ appears on the outer surface, so $E = \dfrac{kq}{r^2}$ again.
The graph is zero up to $R$, falls as $1/r^2$ from $R$ to $a$, is zero from $a$ to $b$, and falls as $1/r^2$ beyond $b$.
Solution by Sreeraj P, M.Sc Physics