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Homework Help: Current carrying wire and Earth’s magnetic field directions

  1. Oct 11, 2011 #1
    1. The problem statement, all variables and given/known data
    A telephone cable at a place has 4 long straight horizontal wires carrying a current of 1 ampere in the same direction east to west. The earth's magnetic field at the place is .39G, the angle of dip is 35°, and the magnetic declination is nearly zero. What are the resultant magnetic fields (magnitude and direction) at points 4cm below the cable?

    2. Relevant equations

    3. The attempt at a solution
    Magnitude of the field due to the current carrying wires is 2x10-5T
    Components of the earth’s magnetic fields –
    Along the horizontal is BHcos35° = 3.19x10-5T
    Along the vertical is BVsin35° = 2.24x10-5T

    According to the right hand rule the magnetic field above the wires should be going into the plane and below should be coming out. I can’t ‘visualise’ the directions of the Earth's magnetic field so I can’t go any further.

    I have numerous questions like this one but I can never see the direction of the earth’s field when it has different angles of dip.

    Attached Files:

    • 2.bmp
      File size:
      186.4 KB
    Last edited: Oct 11, 2011
  2. jcsd
  3. Oct 11, 2011 #2
    This diagram may help you.

    Attached Files:

  4. Oct 12, 2011 #3
    Definitely helped. If only I could 'see' it for myself everytime I get one of these questions. Thanks.
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