Two identical negative point charges are fixed at the vertices and of an equilateral…
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
Two identical negative point charges q=−5.0μC are fixed at the vertices A and B of an equilateral triangle of side length 0.25m. A third point charge Q=+7.0μC is initially held at the third vertex C of the triangle. The charge Q is then slowly moved to a point D that is on the perpendicular bisector of segment AB, a distance 0.40m from the midpoint of AB. Throughout the process the charges at A and B remain fixed.
(a) Calculate the initial total electric potential energy of the three–charge system when Q is at vertex C.
(b) Calculate the final total electric potential energy of the system when Q is at point D.
(c) Determine the work done by the external agent in moving Q from C to D. Include the proper sign in your answer.
(d) Explain the physical meaning of the sign of the work you obtained in part (c) in terms of whether energy was supplied to or extracted from the system.