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Homework Help: Biot-Savart Law for a Point Charge

  1. Jan 10, 2010 #1
    1. The problem statement, all variables and given/known data

    Show that B for a point charge is equal to


    2. Relevant equations

    I'm not all that sure. I read that maxwell's equations can be used to derive this, so I'd imagine that it's


    3. The attempt at a solution

    If it were that, then, if i have a point charge moving at some constant speed along the x axis and I wanted to find B some distance R from it, at that point, I would create a circular path a distance x from the charge with radius R. I can find the electric flux due to the point charge throughout the entire circular disk. Because its moving with constant speed, i can find x(t) which is equal to vt setting my initial location for the charge at x = 0. Also because of the symmetry, B must be the same along the entire path since the charge is the same distance from every point on the path.

    So, the flux as a function of the distance from the point charge is as shown in the picture below

    http://img707.imageshack.us/img707/6956/itsazoo.png [Broken]

    Now that equation really does NOT look like it's going to go anywhere productive so I want to ask if my concepts/setup are right before going any further.
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Jan 12, 2010 #2


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    Homework Helper

    Keep going. Don't give up. Eventually, you will get the Biot-Savart Law.

    (However, remember that you have to get rid of the cross product somehow. v cross r-unit is equal to vsin(theta) in magnitude, so substitute that to get rid of the vectors.)
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