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Homework Help: Magnetic force and fields

  1. Jun 5, 2009 #1
    http://lh6.ggpht.com/_H4Iz7SmBrbk/SikOL1lh7BI/AAAAAAAABCY/_70wWSK_-Vw/s640/DEVAN.jp [Broken]

    given a square wire frame with a side of length L, placed in a constant extarnal magnetic field B, (B=B*[tex]\hat{k}[/tex]). a current of i flows through the frame anticlockwise(as shown by arrows in diagram)

    the frame can turn freely about the x axis (which passes through its centre)
    the frame has a linear mass density of λ

    a) what is the force applied on the frame?
    b) what is the momentum applied of the frame?
    c) what is the angular acceleration of the frame?


    a) since the force applied would be ILxB,
    the force on either side parallel to the field B has no contribution since ILB*sinθ=0 (θ=0/180)
    for either side perpendicular to the field ILxB=ILB

    therefore my total force on the frame would be 0+0+ILB-ILB=0


    b) for the momentum i say that N=RxF=(L/2)*F=(L/2)*ILB=0.5L2IB

    and since i have 2 contributors to the momentum and the are both on x-,

    c) for the angular acceleration α, i need to somehow find the moment of enetria for a frame like this, and then i can say that N=Iα

    can i use the moment of a pole 1/12(mL2) and multiply it by 2 to take into account each side??? this doesnt seem right to me, what aout the other 2 sides wgich arent revolving about their centre???
    Last edited by a moderator: May 4, 2017
  2. jcsd
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