Question

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

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

Answer 1

The correct option is B 0.6 J

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