Question

Two concentric spherical shells of radii a and $1.2$ a have charges $+$Q and $-2$Q respectively. At what distance from centre potential will be same as that of centre?

• A. $2$a
• B. $1.5$a
• C. $2.5$a
• D. $3$a

Answer 1

The correct option is B $1.5$a

Potential at the centre= Potential at the centre

$\frac{kQ}{a}-\frac{2kQ}{1.2a}=\frac{k(Q-2Q)}{x}$

$\Rightarrow \frac{ka}{a}-\frac{2ka}{1.2a}=-\frac{ka}{x}$

$\frac{-0.8}{1.2a}=\frac{1.2-2}{1.2a}=-\frac{1}{x}$

$\Rightarrow x=\frac{1.2a}{0.8}=1.5a$.