A condenser has two conducting plates of radius  10 cm separated by a distance of  5mm. It is charged with a constant current of  0.15A. The magnetic field at a point 2cm from the axis in the gap is

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=μ0Iπr2πR2 ⇒B=μ0ID2πr×rR2    ⇒ B=μ0I2π×rR2 ⇒B=2×10−7×0.15×2×10−210−2                     ⇒ B=6×10−8T