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Homework Help: Magnetic Field Due to Two Parallel Wires

  1. Apr 11, 2010 #1
    1. The problem statement, all variables and given/known data

    A long, straight wire carries a current of 1.7 A in the +z direction and lies along the line x = –3.0 cm, y = 0. A second such wire carries a current of 1.7 A in the +z direction and lies along the line x = +3.0 cm, y = 0, as shown in Figure. Find the magnetic field at a point P on the y axis at y = 6.0 cm.

    2. Relevant equations

    3. The attempt at a solution

    I understood why BL = BR
    In my textbook, the solution says that vector B is the vector sum of vector BL and vector BR.

    I don't understand this:

    It says vector B = -2BL cos (theta) i ( in the -x direction)

    i is the unit vector here

    I have no idea where does the -2BL cos (theta) come from!

    Attached Files:

  2. jcsd
  3. Apr 28, 2010 #2
    Reply people!!
  4. Apr 29, 2010 #3
    What is the magnetic field a distance d from a current carrying wire? Can you exploit the symmetry of the situation?
  5. Apr 29, 2010 #4


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    Staff Emeritus
    Science Advisor
    Gold Member

    Are there no relevant equations?

    This is not an attempt at a solution. This is merely trying to read and understand the given solution. You will do better if you try to solve it by yourself, starting by drawing a figure showing the BL and BR vectors.
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