PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
Three identical point charges, each of magnitude +q, are fixed at the vertices of an equilateral triangle of side length L lying in the xy-plane. A fourth point charge of magnitude +q′ is placed at the centroid (geometric center) of the triangle.
(a) Show that when all three vertex charges remain in place, the net electrostatic force on the central charge is zero. Your answer should include a clear vector argument as well as any necessary symbolic work.
(b) The charge at the top vertex is removed, leaving only the two bottom charges. Derive symbolic expressions for the x- and y-components of the net electrostatic force on the central charge in terms of q, q′, and L. Hence obtain the magnitude of the net force and specify its direction relative to the horizontal base of the triangle.
(c) Using q=6.0μC, q′=1.0μC, and L=0.20m, calculate the numerical value of the net force magnitude found in part (b) and state its direction as an angle measured counter-clockwise from the positive x-axis.