Magnetic Field and Circuits

Discussion in 'Homework Help' started by f74bat, Dec 1, 2008.

  1. f74bat

    Thread Starter Member

    Nov 26, 2008
    13
    0
    Two long, straight parallel wires are separated by a distance d. The bottom wire carries a current 14.0 A.


    [​IMG]

    Point C is at the midpoint between the wires and point O is a distance 0.600d below the bottom wire as shown. The total magnetic field at point O is zero. What is the current, I, in the top wire?

    I did a similar problem in class but we were given more values. I used the B=(mu*I)/(2*pi*r) and then made B1 and B2 equal to one another..but i don't have enough information to solve it.
     
  2. f74bat

    Thread Starter Member

    Nov 26, 2008
    13
    0
    The second part is:

    If the separation distance is d = 0.295 m, what is the magnitude of the magnetic field at point C?
     
  3. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Calculate B at point O due to the current of the bottom wire. Then calculate the current through the top wire as to create an equal magnitude B at point O. The distance of the top wire form point O is (d+0.6d).

    Bottom wire B:

    B1=(μ*I1)/(2π*0.6*d)

    Top wire B:

    B2=(μ*I2)/(2π*(d+0.6*d))=(μ*I1)/(2π*1.6*d)

    Then

    B2=-B1

    thus

    (μ*I1)/(2π*1.6*d)=-(μ*I1)/(2π*0.6*d)

    thus,

    I2=1.6*I1/0.6

    For the second part of the question, calculate B at point C each wire creates and then add them to get the total B (note that one B will come out negative because it is in the opposite direction of the other conductor's B).
     
  4. f74bat

    Thread Starter Member

    Nov 26, 2008
    13
    0
    I had no problem with the first part but what I do I use for part 2?
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    For the second part of the question, you know the current through each wire, calculate B at point C each wire creates and then add them to get the total B (note that one B will come out negative because it is in the opposite direction of the other conductor's B).
     
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