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Homework Help: Having trouble with Helmholtz Coil Experiment Calculations

  1. Mar 26, 2013 #1
    1. The problem statement, all variables and given/known data
    Number of wraps of coil on magnetic moment in field: 100 - N_c
    Number of wraps of coil on Helmholtz coil: 140 - N_h
    Current through magnetic moment: .796A - I_c
    Area of magnetic moment: .37m - A_c
    Radius of Helmholtz coil: .1635m - R_h
    Current through Helmholtz coil to attain equilibrium on balance: 1.32, 2.61,3.91 corresponding to gravitational torques caused by counterweights that are .255m away, .0001g,.0002g,.0003g

    2. Relevant equations
    Bh=(8u_0*N_h*I_h)/(5^(3/2) * R_h)
    as well as T_m = B_h * N_c*I*A_c

    3. The attempt at a solution
    I calculated the three torques both gravitational as well as magnetic based on the formulas provided above. Each time I recieved an answer that was a magnitude of 100 apart. Based on my thinking the T_g and T_m should be equal as the magnetic torque should balance out the gravitational torque. I have checked to make sure all of my units are in SI and I still cannot determine why im not getting the calculations that I should. I also cannot make heads or tails of how the Area of the magnetic moment within the field should have a vector and if it does, how to describe its orientation in space.
  2. jcsd
  3. Mar 27, 2013 #2


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    Staff: Mentor

    Do you get "exactly" 100 as factor between the answers? This would hint to some conversion errors, or a missing factor of N_c somewhere.
    If the factor is 125, the factor of 5^(3/2) is in the wrong part of the fraction.
    Can you show your calculations? I don't see an obvious error here. I think the prefactor 8/(5^(3/2)) is given somewhere?

    A notation like "100 - N_c" is confusing, this looks like a subtraction. Why don't you write 100 = N_c, or (better) N_c = 100?
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