A point charge is fixed at the origin

PHYSICS · Subjective · A Level · Physics · Fields and their consequences · Fields and their consequences

Problem

A point charge q1=4 μCq_1 = 4\,\mu\text{C} is fixed at the origin. A second charge q2=2 μCq_2 = 2\,\mu\text{C} is initially at point AA on the xx-axis, 10 cm10\,\text{cm} away from the origin. The second charge is slowly moved to point BB on the same axis, 20 cm20\,\text{cm} from the origin. (a) Calculate the change in potential energy of the two-charge system during this displacement. (b) Determine the work done by an external agent in moving q2q_2 from AA to BB. (c) State whether the work calculated in part (b) is positive or negative and give a brief reason. Take 1/4πϵ0=9×109 N m2 C−21/4\pi\epsilon_0 = 9 \times 10^9\,\text{N m}^2\text{ C}^{-2}.

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