Question

A hollow metal ball $8cm$ in diameter is given a charge $-4\times 10^{-8}C.$ The potential on the surface of the ball is

• A. zero
• B. -90 V
• C. -9000 V
• D. -900 V

Answer 1

Answer: (C)

The potential on the surface of a ball of radius $R$, is given by
$V=\frac{1}{4\pi {\epsilon }_0}\cdot \frac{Q}{R}$
Given, $R=\frac{8}{2}cm=\frac{8}{2}\times 10^{-2}m$,
$=4\times 10^{-2}m$
$Q=-4\times 10^{-8}C$
$V=9\times 10^9\times \frac{-4\times 10^{-8}}{4\times 10^{-2}}$
$=-9000$ volt