Question

The electric field intensity inside a capacitor is E. Calculate the work done in displacing a charge q over a closed rectangular contour (Fig.).

Answer 1

Answer: A = 0.

Explanation:

The work done in displacing the charge along sides 2,3 and 1,4 is zero, since the force F = qE is perpendicular to the direction of motion (Fig. ). The work done by the force F, on sides 1,2 and 3,4 is the same in magnitude, but opposite in sign. Consequently, the work done over the entire closed contour is zero. This result is valid for all electric fields and closed contours of any shape.