1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Magnitude of a magnetic field a a point

  1. Oct 15, 2014 #1
    A point charge Q moves on the x-axis in the positive direction with a speed of 450 m/s. A point P is on the y-axis at y = +70 mm. The magnetic field produced at point P, as the charge moves through the origin, is equal to -0.8 μT k^. When the charge is at x = +40 mm, what is the magnitude of the magnetic field at point P? (μ0 = 4π × 10-7 T · m/A)

    Hey guys so I am having trouble understanding this problem. Well I actually understand the problem, but I am having trouble applying the formulas.

    I understand that to do that problem I need to use the formula for the magnetic field created by a moving point charge. B=(μ_0 q r x v)/(4π r^2) to solve for the charge.
    I did this for position one where the degree between the angle will be sin(90)=1 and got -.00124C.
    I then applied the equation again to solve for the magnetic field at the new position. My trouble I am having is the cross product between r and v at this locations. I put r into unit vector form and crossed it with v in the positive x direction, but I do not get the right answer.
     
  2. jcsd
  3. Oct 16, 2014 #2

    ehild

    User Avatar
    Homework Helper
    Gold Member

    The formula for B is not correct. It should be [tex]\vec B = \frac {\mu_0}{4\pi} Q \frac{\vec v\times\hat r}{r^2}[/tex]
    so you have to cross the velocity with the unit vector pointing from the charge to P.
    ehild
     
  4. Oct 16, 2014 #3
    Okay, so then I am crossing (450i) x (.O4i-.07j)1/.08. Correct?
     
  5. Oct 16, 2014 #4

    ehild

    User Avatar
    Homework Helper
    Gold Member

    If 0.08 in the denominator stands for ##\sqrt{65}## then it is approximately correct.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted