Figure Q18.11 shows points on several equipotential surfaces, with (a) A positive test...

Figure Q18.11 shows points on several equipotential surfaces, with (a) A positive test charge starts at point A and moves to point C. If the test charge starts and ends at rest, which of the following statements applies? (i) A positive amount of work must be done on the test charge by an external force. (ii) The work done on the test charge by an external force must be negative. (iii) No work is done on the test charge. Repeat this question for moving the test charge (b) from C to E, (c) from B to E, and (d) from D to F.