Two identical point charges +Q are fixed at points A and B that are 20 cm apart in…
PHYSICS · Subjective · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
Two identical point charges +Q are fixed at points A and B that are 20 cm apart in free space.
(i) Define the term "null point" with respect to the electric field of a system of charges.
(ii) Without performing detailed numerical calculations, argue qualitatively where the null point will be located for this system of charges and justify your answer using the principle of superposition.
(iii) A small positive test charge is placed at a point very close to the null point, first on the line AB but slightly nearer to A, and then slightly nearer to B. Explain the direction of the net electrostatic force in each case and comment on the stability of equilibrium at the null point.