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Homework Help: Inductance of a solenoid

  1. Apr 14, 2004 #1
    A solenoid has 140 turns uniformly wrapped around a soft iron core, which has a magnetic permeability =750 Uo (mue sub-knot) diameter of 10.0m and a length of 9.00cm.

    What is the inductance in milli-henry (mH)?

    Did I set this up right? Using L=(uN^2A)/length, you get:

    (750*140^2*pi.005m^2*.09m)/.09m = 1.15E3 Henry = 1.15E6 Milli-Henry

    I think I made a conversion error somewhere. If not, why would they ask for the inductance in milli-henry, and not kilo-henry? :confused:
  2. jcsd
  3. Apr 15, 2004 #2

    Doc Al

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    Staff: Mentor

    Your formula for L is correct. In your arithmetic I see two errors: an extra 0.09m on top, and--most importantly--a missing μ0. The permeability is μ = 750 μ0; μ0 = 4π10-7 N/A2.
  4. Apr 20, 2004 #3
    ohhhhhhhhhhh! Thanks!
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