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Magnetic Field of Two Wires

  1. May 16, 2015 #1
    1. The problem statement, all variables and given/known data


    Two long thin parallel wires a distance d = 14.6 cm apart carry 25-A currents (I) in the same direction. The magnetic field is measured at point P, a distance d1 = 12.1 cm from the lower wire and a distance d2 = 5.8 cm from the upper wire.

    a. Find the x and y components of the magnetic field at P due to the current in the lower wire only.

    b. Find the x and y components of the magnetic field at P due to the current in the upper wire only.

    c. Determine the magnitude |B| of the total magnetic field at P.
    2. Relevant equations

    B = mu0/2 pi * I/d

    3. The attempt at a solution

    to find B1x :

    = -Bcos 30

    -mu0/2*pi *25/.121 *sqrt3/2

    this isn't the right answer, since the rest of the problems are the same way, I need to make sure I understand what I'm doing wrong before moving on. Someone please help!
  2. jcsd
  3. May 16, 2015 #2
    Did you draw the picture? From the given information there are two points that satisfy the given info.

    Suggestion, draw the diagram above with the magnetic field vectors at point p from both wires. The magnitudes of the vectors is easy, and you should know the general directions of both vectors, the rest is trig.?
  4. May 16, 2015 #3
    Wouldn't the field be going the same way from both wires? Then what would the x and y look like if the field is just one on top of the other going the same way?
  5. May 16, 2015 #4
    The two vectors will be approximately perpendicular at point p, right? Draw the magnetic field lines that go around each wire and also go through point p from each current, they are circles, right?
  6. May 16, 2015 #5
    The field lines are going to the left on both wires. so I'm confused what direction they would be at point P
  7. May 16, 2015 #6
    The magnetic field from the top wire will be pointing roughly in the 1o'clock direction and the field other wire will point in roughly the 10 o'clock direction?
  8. May 16, 2015 #7

    rude man

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    Homework Helper
    Gold Member

    Where did you get the 30 degrees? Careful, this is not a right-angled triangle.
    Suggestion: determine the three inner angles first.
  9. May 16, 2015 #8

    Like this but reverse the red arrow.
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