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Q.
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
Electrostatic Potential and Capacitance
Solution:
Here $r = 18 \,cm=18\times10^{-2}\, m$,
$q=5\times10^{-6}\, C $
As $C=4\pi\varepsilon_{0} r=\frac{18\times10^{-2}}{9\times10^{9}}=2\times10^{-11}\, F$
Energy of charged conductor is
$U=\frac{q^{2}}{2C}=\frac{\left(5\times10^{-6}\right)^{2}C}{2\times2\times10^{-11}\,F}$
$=0.625\, J$