PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
Two point charges q1 and q2 are fixed at a separation r. Answer the following without carrying out detailed numerical calculations unless asked to do so.
(i) Explain how the direction of the electrostatic force on each charge depends on the algebraic signs of q1 and q2.
(ii) The charges are immersed in a medium of relative permittivity εr. Describe qualitatively how the magnitude of the force changes compared to its value in vacuum and give the physical reason for this change.
(iii) If εr=4, by what factor does the magnitude of the force change? Justify your answer.