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Current passing through a loop

  1. Dec 11, 2013 #1
    1. The problem statement, all variables and given/known data

    A current of 5 A is passed through a single wire loop, producing a magnetic field of 3.4 x 10^-3 T at the center. What is the radius of the loop?

    2. Relevant equations

    B = μNi / 2r

    3. The attempt at a solution

    B = 3.4 x 10^-3
    N = 1
    i = 5

    B = μNi / 2r
    3.4 x 10^-3 = (__)(1loop)(5 A) / 2r

    what is this u variable ? what does it represent
     
  2. jcsd
  3. Dec 11, 2013 #2

    Pythagorean

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    it's the greek letter, mu, and it's the permeability of the substance with respect to the magnetic field. Often, your substance is air, which can be (very accurately) approximated by the vacuum permeability.

    Try googling "magnetic constant" ;)
     
  4. Dec 11, 2013 #3
    i found a value for it.. 4∏ x10^-7
    but the rest of the question goes like this then
    = (3.14x10^-6)/2r
    = 1.57 x 10^-6/r

    3.4 x 10^-3 = 1.57 x 10^-6/r

    1.57 x 10^-6 = 3.4 x 10^-3 r
    4.62x10^-4 = r

    0.0004617647059 m

    this doesnt seem right
     
  5. Dec 11, 2013 #4

    Pythagorean

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    Your first line (with =) looks wrong 3.14x10^-6?
     
  6. Dec 11, 2013 #5
    redid the first line got the new answer of 6.28x10^-6 not sure of my miscaculation. this resulted in the new answer of .924m seems more plausible.
     
  7. Dec 11, 2013 #6

    Pythagorean

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  8. Dec 11, 2013 #7
    i actually tried using that but not to sure on all of its function, as soon as i enter 5 A it calculates everything
     
  9. Dec 11, 2013 #8

    Pythagorean

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    you have to enter I and R and it will give you B. Don't need to worry about z, since you're doing center of loop.
     
  10. Dec 11, 2013 #9
    i entered my .9m and 5 A to get a B of 0.000003399992 what does this tell me ?
     
  11. Dec 11, 2013 #10

    Pythagorean

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    let's assume hyperphysics is right, first. What does that tell you?
     
  12. Dec 11, 2013 #11
    well that somewhere in my calculations i am wrong. redid it to get 9.2x10^-4 which when plugged into the site is correct
     
  13. Dec 11, 2013 #12

    Pythagorean

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    congrats :)
     
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