A solid copper ball of radius r_i and carrying charge -q is placed inside a hollowed silver sphere of radius r_o and charge +q. Insulators are used to hold the copper sphere in place inside the silver sphere. Derive an expression for the electric field magnitude between the two spheres. Express E(r) you derived using V_io, the potential of the copper ball relative to the silver shell.

A conducting solid sphere  (radius r_i) with charge -q is located at the center of a conducting hollowed sphere (radius r_o) with charge +q. Non-conducting supports are used to hold and maintain the solid sphere at the center of the hollowed sphere. Taking potential to be zero at r = ∞, determine the electric potential (V_r) at i) inside the solid sphere ii) between the two spheres iii) Outside the hollowed sphere. Hint: Potential at a point is the sum of potentials from each sphere.

Consider two metallic globes. The smaller globe has a negative charge of magnitude 4.0 µC, while the larger globe, which is thrice the diameter of the first, is initially electrically neutral. A long, thin metallic strip, is then used to connect the two globes. Determine the resulting charge on each globe.