Practice question

**System of charges** potential energy is sum over pairs U = Σ k q_i q_j/r_ij, work required to assemble charges from infinity. For 28 μC and -14 μC, 0.28 m apart, U=9×10⁹×28×(-14)×10⁻¹²/0.28= -12.6 J, negative indicates bound system. When a charged conductor (charge Q ) is placed inside a larger uncharged hollow conductor, the electric field from the inner charge induces -Q on the inner surface of the hollow conductor to ensure the field inside the conductor's material is zero. Since the hollow conductor is initially uncharged, its total charge must remain zero, so +Q appears on its outer surface to balance the induced -Q