Question
A point charge Q is placed at the origin. Find the electrostatic energy stored outside the sphere of radius R centred at the origin.
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Answer
Charge = QRadius of sphere = R
$\therefore$ Capacitance of the sphere $=\text{C}=4\pi\in_0\text{R}$
Energy $=\frac{1}{2}\frac{\text{Q}^2}{\text{C}}=\frac{1}{2}\frac{\text{Q}^2}{4\pi\in_0\text{R}}=\frac{\text{Q}^2}{8\pi\in_0\text{R}}$
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