Practice question

**Electrostatic shielding** inside hollow conducting shell field zero when no charges inside, regardless of external field, because free charges redistribute on outer surface to cancel external field inside conductor, E=0 inside material in equilibrium, consequence of Gauss's law and conductor property. The potential energy between two point charges is U = (1/4 π ε₀) (q₁ q₂/r) , where r is the distance between them. This expression depends only on the magnitude of the separation r , not on the direction or orientation of the line joining the charges in space, because the Coulomb force is isotropic (depends only on distance) and the potential is a