Electric field energy density
= Electric field energy density
{title2=$u_E=\epsilon_0|E|^2/2$}
The local energy per unit volume associated with an <electric field> in vacuum is $u_E=\epsilon_0|E|^2/2$. Its volume <integral> gives the electric contribution to the <electromagnetic energy>. For a static field outside an isolated charged <conducting sphere>, integrating this density from its radius to infinity gives the <electrostatic energy> $Q^2/(8\pi\epsilon_0R)$.