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Homework Help: Inductance of a coil for a given emf and current change

  1. Oct 21, 2005 #1

    My Question:

    What is the inductance of a coil if the coil produces an emf of 2.50V when the current in it changes form -28.0 mA to 31.0 mA in 12.0 ms?

    For this I know I will need to use this equation:

    E=-M(delta I)/(delta t)

    My problem is that I was wondering if coming up with a negative inductance is alright.

    Thank You :smile:
  2. jcsd
  3. Oct 21, 2005 #2


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    No. The inductance is positive. The induced EMF opposes the increasing current (Lenz's Law) which means that E must be negative (-2.50 V) in your example.
  4. Oct 22, 2005 #3
    So this work is fine then

    E=-M(delta I)/(delta t)
    2.50 V=(-M((31*10^-3 A) - (-28*10^-3 A)))/(12*10^-3 s)
    2.50 V= -M(4.92 A/s)
    -M=.51 H
    M=-.51 H

    Thank You:smile:
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