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A coil of 25 turns of wire is suspended by a thread

  1. Jul 8, 2015 #1
    1. The problem statement, all variables and given/known data

    A coil of 25 turns of wire is suspended by a thread. When a current flows through the coil, the tension in the thread is reduced by 4.0 ´10-2N.
    http://members.shaw.ca/barry-barclay/Self-Tests/test11/Magnet20.gif

    2. Relevant equations
    F=IBL
    B=nμI



    3. The attempt at a solution
    I have been driving myself nuts with this question haha but here is my attempt.

    The force against gravity has to come from the current so I tried

    0.04 = I (0.065)(0.15)
    I = 4.1a
    , which is incorrect

    then I tried combining the two

    to get
    I=√F/Nμ

    but that left me with 35.68

    So I am at a loss as to how to go about this , any help would be great! or any formulas I am missing. I have not done calc yet this is all supposed to be simple algebra however this process for this particular question eludes me and it is the last of the set of 190 , I want it done! haha

    Correct answer is .16 amps I know it has to go counterclockwise for the force to be pushing up


     
  2. jcsd
  3. Jul 8, 2015 #2

    TSny

    User Avatar
    Homework Helper
    Gold Member

    Did you take into account that there are 25 wraps of wire?
     
  4. Jul 8, 2015 #3
    Haha I did however I did 0.04 = I 0.065x25x0.15, not 0.04 = I 0.065x(25x0.15)

    Thank you so much lol, i knew it was simple but it was killing my soul with frustration
     
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