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Homework Help: Determine inductance of a solenoid

  1. Mar 8, 2010 #1
    1. The problem statement, all variables and given/known data
    Determine the inductance of a solenoid with 650 turns in a length of 21 cm. The circular cross section of the solenoid has a radius of 4.2 cm.


    2. Relevant equations

    ???

    3. The attempt at a solution I've looked all over my textbook and cant come up with a possible equation(s). Help!!!
     
  2. jcsd
  3. Mar 8, 2010 #2

    rl.bhat

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    Re: Inductance

    L = μo*N^2*A/l.
    where N is number of turns,
    A area of cross section of the coil and
    l is the length of the coil.
     
  4. Mar 8, 2010 #3
    Re: Inductance

    Ok so I did L = (1.26e-6)(650)^2(.00882) / .21 = 2.24e-2 H = 22.4mH. I got it wrong however. Where did I go wrong?
     
  5. Mar 8, 2010 #4

    rl.bhat

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    Re: Inductance

    Check the area of the coil.
     
  6. Mar 8, 2010 #5
    Re: Inductance

    would area = .01764? (radius^2 (in meters) * .21)
     
  7. Mar 8, 2010 #6

    rl.bhat

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    Re: Inductance

    Area of cross section of the coil is π*r^2.
     
  8. Mar 9, 2010 #7
    Re: Inductance

    ok i'm an idiot. i got it wrong again. this was my equation: L = (1.26e-6)(650)^2(1.1466)/.21. i multiplied that answer by 1000 to get mH
     
  9. Mar 9, 2010 #8

    rl.bhat

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    Re: Inductance

    (1.1466)/
    How did you get this?
    Area = π*(4.2*10^-2)^2 m^2 = 55.42*10^-4 m^2
     
  10. Mar 9, 2010 #9
    Re: Inductance

    ok i got it! i used n = 650 (is that not what n is?). Anyways... thanks for all your help (and patience). I really appreciate it!
     
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