Faraday Physics Problem?

roy

The current in a 4.70 mH inductor decays over time according to the following function, where t is in seconds.

I(t)=(.943 A)e^-396t

How long does it take the emf to drop below 1.25 mV?

The derivative of the equation is -373. 43e^-396t I believe.

physicsdude

emf = -LdI/dt

= -(4.7x10^-3) (-373. 43e^-396t) = 1.25x10^-3

Now solve for t:

e^-396t = 7.12x10^-4

-396t = ln(7.12x10^-4)

t = 1.83 x 10^-2 sec