Two point charges (at ) and (at ) are fixed on the x–axis in vacuum.
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
Two point charges +q (at x=−a) and +4q (at x=+a) are fixed on the x–axis in vacuum.
(a) Derive the coordinates of all points on the x–axis where the electric field is zero.
(b) A small positive test charge is now released from rest at each null point found in part (a). For every null point, analyse qualitatively the direction of the initial acceleration of the test charge if it is displaced slightly along the x–axis. Classify each null point as a point of stable, unstable or neutral equilibrium, giving reasons.
(c) Comment on whether any null point exists off the x–axis in the x–y plane for the given charge configuration.