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Homework Help: Find the magnitude of the magnetic field 10 cm from the wire

  1. Nov 14, 2011 #1
    1. The problem statement, all variables and given/known data

    A) Find the magnitude of the magnetic field 10 cm away from the wire at point P as shown in the picture. The current is directed along the x-axis.

    B) Find its direction

    Info: I = 5 amps. Point P lies on the Y-axis. Current on the X-axis.

    Picture (I have drawn): http://twitpic.com/7e0l7e [Broken]

    2. Relevant equations

    I THINK: B=u*I/2*pi*r

    3. The attempt at a solution

    B = (4pi * 10^(-7)) * 5/2 *pi * .1m = 7.85 * 10^(-8) N

    ***I am not sure if this is correct. I have no means to check my work, so I am hoping someone can simply tell me whether or not I am correct, and if not, perhaps enlightening me as to which direction I should head to find the right answer. Much thanks.
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Nov 14, 2011 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Better to write it like this:
    [tex]B = \frac{\mu_0 I}{2 \pi r}[/tex]

    Redo your calculation.
  4. Nov 14, 2011 #3

    Thank you, Doc Al. I redid my calculation in that format and got 7.96E-7. Does that seem correct?

    Again, thank you.
  5. Nov 14, 2011 #4

    Doc Al

    User Avatar

    Staff: Mentor

    Not exactly. When you plug in the value of μ0 = 4*pi*10^(-7), that pi will cancel with the pi in the denominator. So you should be able to do the entire calculation without touching a calculator.

    Try it one more time. :smile:
  6. Nov 14, 2011 #5

    Aaah, got it. That should've been evident from the beginning. :redface: Thank you, Doc Al. You have alleviated me some frustration. :smile:
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