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Inductance formulas

  • Thread starter r_swayze
  • Start date
  • #1
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Homework Statement



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

I(t) = (.943A) e-(396 s-1) t)

(a) What is the induced emf across the inductor at t= 5.00 ms? (b) How long does it take the emf to drop below 1.25 mV?


The Attempt at a Solution




Since emf = -L(dI/dt) , I can take the derivative of the function above and plug in t=.005, right?

I' = (.943A) e-(396 s-1) t) (-1/396s)

Plug in t=.005 and I get I' = -.00238

emf = -L(dI/dt)

emf = -(.0047)(-.00238) = 1.119x10-5

I tried this answer but it was incorrect. What am I doing wrong?
 

Answers and Replies

  • #2
rl.bhat
Homework Helper
4,433
5
You have not taken into account the term e^-396*t.
 

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