An eddy current is a residual current which flows after time-varying electric E and magnetic fields B are removed. In cgs,
for slowly varying fields, where c is the speed of light, J is the current density, and
is the conductivity. Combining (2) and (3) gives
which is a diffusion equation with diffusion coefficient
The diffusion time for decay of the eddy current is therefore
where L is the length scale.
(1)
(2)
(3)
for slowly varying fields, where c is the speed of light, J is the current density, and
is the conductivity. Combining (2) and (3) gives(4)
(5)
which is a diffusion equation with diffusion coefficient
(6)
The diffusion time for decay of the eddy current is therefore
(7)
where L is the length scale.
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