Question

A metallic sphere of radius $18cm$ has been given a charge of $5\times 10^{-6}C$ The energy of the charged conductor is

• A. $0.2J$
• B. $0.6J$
• C. $1.2J$
• D. $2.4J$

Answer 1

Answer: (B)

Here $r=18cm=18\times 10^{-2}m$,
$q=5\times 10^{-6}C$
As $C=4\pi {\epsilon }_{0}r=\frac{18\times 10^{-2}}{9\times 10^9}=2\times 10^{-11}F$
Energy of charged conductor is
$U=\frac{q^2}{2C}=\frac{{\left(5\times 10^{-6}\right)}^{2}C}{2\times 2\times 10^{-11}F}$
$=0.625J$