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Homework Help: Inductance Of A Solenoid Problem!

  1. Feb 22, 2012 #1
    1. The problem statement, all variables and given/known data

    A solenoid is wound with a single layer of insulated copper wire of diameter 2.100 mm and has a diameter of 3.000 cm and is 1.900 m long. Assume that adjacent wires touch and that insulation thickness is negligible.

    a) How many turns are on the solenoid?
    Solved: determined to be 904

    b)What is the inductance per meter (H/m) for the solenoid near its center?

    2. Relevant equations

    Inductance = (constant mu0)* (N^2)*A / l

    mu0 = 4*PI*10^-7
    N = 904 turns
    A = PI*R^2 (R = 2.100 mm/2)
    l = length of solenoid = 1.900 m

    3. The attempt at a solution

    Plugged all those variables above (converted R to meters) and got 0.00019 for the inductance.

    I don't understand what it means to find the Inductance per Meter at the center of the solenoid? Do I have to divide by 1.900 m again? Confused as to what I'm supposed to do.
  2. jcsd
  3. Feb 25, 2012 #2


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    Science Advisor
    Homework Helper

    hi pierretong! :smile:
    yes, your formula µN2A/l gives the inductance of the whole solenoid

    so divide by l again for the inductance per metre :wink:

    (if you cut the solenoid into x pieces, then for one piece N2 would be 1/x2, so N2/l would be 1/x)

    see also http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/indcur.html#c2 and http://hyperphysics.phy-astr.gsu.edu/hbase/electric/indsol.html
  4. Feb 25, 2012 #3


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    Staff: Mentor

    Check the area calculation. You want the cross sectional area of the solenoid, so which radius should you use?
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