Question

Two concentric conducting shells of radius $a$ and $b$ $(>a)$ carry charges $Q$ and $-2Q$, respectively. The correct variation of electric intensity $E$ as a function of $r$ is given by

• A.
• B.
• C.
• D.

Answer 1

Answer: (B)

The inner face of the outer shell has the charge $-Q$
and its outer face also has the charge $-Q$.

The final charge distribution on each face of shells is shown in figure. The expression for electric field is
given by $E=\frac{kQ}{r^2}$ for $a<r<b$ (radially outwards)
And $E=-\frac{kQ}{r^2}$ for $r>b$ (radially inwards)
Note that the field in the outward direction is assumed to be positive.