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Unformatted text preview: HW-11 1.Consider a capacitor consisting two metal circular disks (radius R) separated by a distance d. Assuming d<<R and ignore the edge effect. The capacitor starts to be charged at t=0 with a constant current I, and the charges distribute uniformly over the metal plate. (a) Find the electric field and the magnetic field between the capacitor. (b) Find the energy density uemand the Poynting vector. (c) Determine the total energy in the capacitor, as a function of time. Calculate the total power flowing into the capacitor, by integrating the Poynting vector over the appropriate surface. Check that the input power is equal to the rate of the increased total energy.Solution:(a)The charge on the metal plate comes from the accumulation from the current. Thus IdtdQ. With I=const and that Q=0 at t=0, we have Q(t)=It.Then the surface charge density is 2RQ. The electric field is 22RItRQE. Inside the capacitor, there is no free current but the displacement current....
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- Fall '09