Two point charges of +6 ,µC and ,-2 ,µC are fixed a distance apart in air
PHYSICS · Subjective · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
Two point charges of +6\,µC and \,-2\,µC are fixed a distance d=0.25m apart in air.
(a) Derive an expression for the distance d′ at which the same pair of charges would experience the same magnitude of force when the entire region is filled with an oil of relative permittivity εr=5.
(b) Calculate the value of d′.
(c) Suppose now that the oil occupies exactly half of the straight-line region between the charges while the remaining half is still air. Assuming the effective permittivity along the line may be taken as the simple average of the two media, estimate the force acting between the charges when they are kept at the original separation d. State whether this force is attractive or repulsive.