# Induced magnetic fields

1. Dec 3, 2008

### StephenDoty

A parallel-plate capacitor, C=5 mircoF, has closely spaced circular plates of radius R = .1m.

How much displacement current is encircled in a loop of r=.05m that is centered on the axis between the plates when a uniform electric field between these plates changes with time at the rate of 9*10^12 V/ms during the charging process? What is the magnitude of the induced magnetic field at r=.05m?

Dissipative current = $$\epsilon$$_0 * d$$\phi$$_e/dt
or $$\epsilon$$_0 * A *dE/dt

And for the magnetic field B =($$\epsilon$$_0 * $$\mu$$_0 * A *dE/dt)/ 2*pi*r

Now is A equal to pi*r^2 where r is equal to .05m since this is the area that the flux is going through or does A equal the ratio of the areas, r^2/R^2, since there is flux through the whole .1m radius?

Thanks.
Stephen