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Homework Help: Net Magnetic Field at the Center of a Loop and X Distance Away From a Wire

  1. Mar 21, 2012 #1
    1. The problem statement, all variables and given/known data
    https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-prn1/553004_1959186995753_1725123128_934768_456680196_n.jpg [Broken]
    In case the words are too small:
    I2= 6.61I1
    The net magnetic field at center of loop is 0.
    I'm looking for the radius of the loop

    2. Relevant equations
    for straight wire: B=(u0*I)/(2[itex]\pi[/itex]*r)
    for loop: B= (u0*I)/(2*r)

    3. The attempt at a solution
    So, since the two magnetic fields are perpendicular to each other: √(B12+B22)=0
    I tried to find H in terms of R by using the right hand rule. I2/I1=(B2*H*[itex]\pi[/itex])/(B1*R) so H= -(6.61R/[itex]\pi[/itex])
    But now I'm stuck, and I don't know if my work so far is even right.
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Mar 22, 2012 #2


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    Science Advisor
    Homework Helper

    Hi BornSurvivor! :smile:

    (pleeeeeease don't post such wide images! :redface:)
    No, a loop current's magnetic field goes along the axis of the loop,

    and a straight line current's magnetic field goes in loops around the line. :wink:
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