Question

A positive point charge (q = +5.4 10-8 C) is surrounded by an equipotential surface A, which has a radius of rA = 1.5 m. A positive test charge (q0 = +4.8 10-11 C) moves from surface A to another equipotential surface B, which has a radius rB. The work done by the electric force as the test charge moves from surface A to surface B is WAB = -7.7 10-9 J. Find rB.

Answer 1

Work=INT force*dr
= INT kqqdr/r^2= -kqq /r evaluated at ra, rb

solve for rb.