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Perpendicular wires carrying current, torque

  1. Oct 30, 2014 #1
    1. The problem statement, all variables and given/known data

    Two thin wires of length [tex] L_1, L_2 [/tex] were placed perpendicular to each other in half of their lengths. Wires are carrying current [tex] I_1[/tex] and [tex] I_2. [/tex] Find the torque on each of those wires.
    2. Relevant equations

    [tex] \tau = \mu \times B = r \times F [/tex]
    3. The attempt at a solution
    To calculate the force I need the magnetic field, which I don't really know how to calculate in this problem. Calculating the magnetic dipole moment would require surface area, which I guess is zero(wires are infinitely thin) so it's a dead end. In parallel lines problem I could calculate magnetic field and force easily in any point in space, but I guess I can't really do that here because there is no distance between the wires. Where should I start?
  2. jcsd
  3. Oct 30, 2014 #2


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    Hello zzz and welcome to PF.

    Re distance:
    The thing to do is not to let that lack of info stop you: call this distance d, or use 1 m to begin with, whatever. Perhaps it cancels later on...

    Re μ: doesn't appear , so I don't know what it stands for here ;)

    Re: magnetic field: you should be able to find something on the magnetic field due to a current carrying wire...(If you can for parallel wires, you can also do it for perpendicular ones: B fields simply add up -- and wire 2 only "feels" the field from 1 anyway)

    (By the same token as the distance: B field of infinitley long wire to begin with: what changes (strength, direction) if length is finite...)
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