A point charge +Q is placed at the centre of an isolated conducting shell of radius R. Find the electrostatic potential energy stored outside the spherical shell if the shell also contains a charge +Q distributed uniformly over it.
dU/dV=(1/2)εoE2, where V is volume, U is potential energy.
The Attempt at a Solution
The charge +Q inside the conductor will induce -Q charge on the inside surface, which further leads to +2Q charge on the outer surface of the shell. Therefore E=2kQ/r2.
My question is, why have we used the formula dU/dV=(1/2)εoE2. How did we derive it? Isn't it equal to the energy of a charged capacitor.
Sorry if this a bad question, I just want to know how did we derive this formula.