A parallel-plate capacitor has closely spaced circular plates of radius R = 3.00 cm.Charge is flowing onto the positive plate at the rate I = dQ/dt = 3.65 A.The magnetic field at a distance r = 1.50 cm from the axis of the plates is approximately
A)135 mT
B)256 $\mu$T
C)1.35 $\mu$T
D)457 mT
E)88.3 $\mu$T

Question

Quizplus · Accepted Answer

The magnetic field at a distance r from a current-carrying wire is given by B = μ0I/2πr, where μ0 is the permeability constant and I is the current.
In this case, we can consider the circular plate as a current-carrying wire with a current of I = dQ/dt = 3.65 A flowing onto it. The magnetic field at a distance r from the axis of the plates is then given by B = μ0I/2πr = (4π×10-7 T·m/A)×(3.65 A)/(2π×0.015 m) ≈ 1.35 μT ≈ 1.35×10-3 T.
Therefore, the best choice is C.

A Parallel-Plate Capacitor Has Closely Spaced Circular Plates of Radius μ\muμ

A Parallel-Plate Capacitor Has Closely Spaced Circular Plates of Radius $\mu$