1. Two equipotential surfaces surround a +1.60 x 10^-8-C point charge. How far is the 280-V surface from the 74.0-V surface?

2. A positive point charge (q = +8.79 10^-8 C) is surrounded by an equipotential surface A, which has a radius of r_A = 1.69 m. A positive test charge (q₀ = +4.30 10^-11 C) moves from surface A to another equipotential surface B, which has a radius r_B. The work done by the electric force as the test charge moves from surface A to surface B is W_AB = -6.94 10^-9 J. Find r_B.

3. The drawing shows a set of equipotential surfaces seen in cross-sections. Each is labeled according to its electric potential. A 2.2 x 10^-7 C point charge is placed at position A. Find the work done on the point charge by the electric force when it is moved (a) from A to B, and (b) A to C.