What happens to the force between two charges if the distance between them is (a) halved (b) doubled?

Explanation

From Coulombs law, `F prop 1/d^(2)`. So
(a) When distance is reduced to half, force increases by four times. `[ :' F_(2)=(F_(1)d_(1)^(2))/((d_(1))/2)^(2)=4 F_(1)]`
(b) When distance is doubled, then force is reduced by four times. `[ :' F_(2)=(F_(1)d^(2))/(|2d_(1)|^(2))=1/4 F_(1)]`