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Homework Help: Flux density

  1. Aug 13, 2009 #1
    1. The problem statement, all variables and given/known data
    A current flows in a circular loop consisting of a single turn.If the same wire is bent into a circular loop of 2 turns and the same current is passed through the loop,the magnetic flux density at the centre will change by a factor of ...?
    (ans: 4 )

    Relevant equations

    B = (mu0 * N*I)/2r

    The attempt at a solution

    For the 1st loop,
    B = (mu0 *I)/2r

    To find B' after bending,
    the length of the wire remains unchanged = 2*pi*r
    so to form 2 circular loops the radius has to be halved for each loop?
    which makes
    B' = (mu0 * N*I)/(2r/2)
    B' = (mu0 * 2*I)/(r) ?

    so change in flux = B-B'/B
    = 3

    Thanks in advance.
  2. jcsd
  3. Aug 13, 2009 #2


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    Homework Helper

    flux density at the centre will change by a factor of ...?
    Chang by factor means you have to take the ratio, not the difference.
    In the problem n will be doubled and r reduces to half.
  4. Aug 13, 2009 #3
    Oh I get it now.
    Thank you very much!
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