A parallel-plate capacitor with circular plates 21.6 cm in diameter is being charged. The displacement current density throughout the region is uniform, into the paper in the diagram, and has a value of . We have to calculate (a) the magnetic field B at a distance from the axis of symmetry of the region. (b) We have to calculate in this region.

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(a)

Ampere’s law as extended by Maxwell is

Where

There will not be conduction current between the plates of a capacitor; therefore, in this region magnetic field will be due to the displacement current only. We consider an Amperian loop of radius . Applying the Maxwell modified Ampere’s law, we get

(b)

We calculate next in this region.