The figure shows two plates A and B. Plate A has a potential of 0 V and plate B a potential of 100 V. The dotted lines represent equipotential lines of 25, 50, and 75 V. A positive test charge of 1.6 × 10^-¹⁹ C at point x is transferred to point z. The energy gained or expended by the test charge is

Question

Quizplus · Accepted Answer

The test charge moves from point x to point z along an equipotential line of 50 V. Therefore, no work is done by the electric field. However, since the test charge moves from a point of lower potential (x) to a point of higher potential (z), the work done by the test charge is negative (i.e. expended). The energy expended by the test charge is given by: W = qΔV = (1.6 × 10^-¹⁹ C)(100 V - 0 V) = 160 J However, we must remember that the test charge actually moves along an arc between x and z, rather than a straight line. This means that the actual work done may be slightly different from the above calculation, but we can assume that B is the closest answer choice.

The Figure Shows Two Plates a and B