A capacitor is made of two circular plates each of radius 1m. It is being charged by an external source. Find the magnetic field at a distance of 2m from the center of the plate in the plane midway between them, when the charging current is 2A.

detailed solution

Correct option is B

Consider a loop of radius 'r' between the two circular plates, placed axially with them. The area of the loop, A'=πr2 By symmetry magnetic field induction B→ is equal in magnitude and is tangential to the circle at every point In this case, only displacement current  ID, will cross the loop. Therefore, using Ampere’s Maxwell law, we have ∮B→.dl→=μ0ID⇒2πrB=μ0×(current passing through the area A') ⇒ 2πrB=μ0ID  [Since r>R, ID=I] ⇒B=μ0ID2πr   ⇒B=2×10−7×2×12                     ⇒ B=2×10−7T