Uniformly charged solid sphere (total charge Q, radius R): Outside (r >= R): E = kQ/r^2 (same as point charge at center). Inside (r < R): E = kQr/R^3 = rhor/(3epsilon_0). Field increases linearly from center to surface, then falls as 1/r^2.

Conducting sphere (charge Q on surface): Outside (r >= R): E = kQ/r^2. Inside (r < R): E = 0 (charge resides only on surface). Surface: E = sigma/epsilon_0 just outside.

Concentric shells: Apply Gauss's law region by region. Enclosed charge changes at each shell boundary. In the conducting material of each shell, E = 0, which determines induced surface charges.