Two fixed point charges (at ) and (at ) are kept on the -axis in vacuum.
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
Two fixed point charges q1 (at x=0) and q2 (at x=d) are kept on the x-axis in vacuum.
(i) Derive a general expression for the coordinate(s) x (measured from the origin) at which a third test charge q placed on the x-axis experiences zero net electrostatic force.
(ii) Using your expression, obtain the condition on the signs and relative magnitudes of q1 and q2 for the null point to lie between the two fixed charges.
(iii) Prove that if the null point lies outside the segment joining the charges, it is always located closer to the charge having the smaller magnitude of charge.