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. $0.62J$
• C. $1.2J$
• D. $2.4J$

Answer 1

Answer: (B)

$0.62J$

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