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Homework Help: Find current when linear mass density and current is given.

  1. Jul 1, 2012 #1
    1. The problem statement, all variables and given/known data
    A long straight wire is fixed horizontally and carries a current of 50 A. A second wire having linear mass density 1.0 * 10^{-4} is placed parallel to and directly above this wire at a separation of 5mm. What current should this second wire carry such that the magnetic repulsion can balance its weight?
    Equations relevant
    (B = μ0i)/2∏r
    F = B * I * L * sina
    My attempt
    I have first got the magnetic field of Wire1 by the formula (B = μ0i)/2∏r.
    Then i took out the Mg Field of Wire2 with the same formula taking current as I.Then i took the weight of Wire2 as Total Force and calculated---
    Ftotal=B * I * L + B1 * I1 * L1 (taking L as 1m and where B1,L1,I1 as values of Wire2
    But i dont get the right answer that is 0.49A.
    Last edited: Jul 1, 2012
  2. jcsd
  3. Jul 1, 2012 #2
    Hi arunashish. Welcome to PF.

    How have you attempted the problem? What do you think would be the equations relevant here?

    Please follow the homework-help template while posting questions in this section :smile:
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