Question

Figure shows two conducting thin concentric shells of radii $r$ and $3 r .$ The outer shell carries charge $q .$ Inner shell is neutral. Find the charge that will flow from inner shell to earth after the switch $S$ is closed.

• A. $-\frac{q}{3}$
• B. $+\frac{q}{2}$
• C. $-\frac{q}{2}$
• D. $+\frac{q}{3}$

Answer 1

Answer: (D)

Let $q_{1}$ be the final charge on inner shell.
So, potential of inner shell must be zero
$\frac{ Kq }{3 r }+ \frac{ Kq _{1}}{ r }=0$
$\Rightarrow q _{1}=\frac{- q }{3}$
so $\frac{q}{3}$ charge from shell must flow towards earth.