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Self-inductance of an inductor - theoretical vs measurment

  1. Dec 8, 2008 #1
    Hi,

    I did an experiment where one of the 'questions' was to determine the self-inductance of an inductor. I am going to leave out the experimental method, but if you need to know just say so and I'll try to explain.

    The value I got was [tex]L = (3.910 \pm 0.009) \text{ mH}[/tex].

    I am fairly confident that this is correct, because 4 people who did the experiment before me got the same value, and my teachers also confirmed that was the result we are looking for.

    Now, I need to compare this value to the value obtained from the theoretical formulas.

    I used the following:
    [tex]L = \frac{N \Phi}{i}[/tex]
    [tex]\Phi = BA[/tex]
    [tex]B = \frac{\mu_0 N i }{\ell}[/tex]

    So
    [tex]L = \frac{\mu_0 N^2 A}{\ell}[/tex]
    (N is the number of turns, A is the cross-sectional area, [tex]\ell[/tex] is the length of the inductor and i is the current.

    Plugging in the values for A, l, N etc, I get a value of L = 1.79 mH.

    I am about a factor 2 off..? How did this happen?

    I was wondering if this could be because of the many assumptions (that may not be true here) and approximations for example for the magnetic field of an inductor (which assumes a very long inductor if i remember correctly...)?

    Could that really cause such a large error? I doubt it... But if they are correct that would mean 4 people + my teacher measured the inductance wrongly?
     
  2. jcsd
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