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Homework Help: Magnitude of the net force that acts on the charge

  1. Jul 27, 2005 #1
    A magnetic field has a magnitude of 1.2 10-3 T, and an electric field has a magnitude of 6.0 103 N/C. Both fields point in the same direction. A positive 1.8 µC charge moves at a speed of 2.6 106 m/s in a direction that is perpendicular to both fields. Determine the magnitude of the net force that acts on the charge.

    Okay, i know that Fnet=the square root of Fe^2+Fb^2, and after drawing a diagram, i think that they are 2 perpendicular forces, but I don't know what to plug in to the equation, or where to begin. :confused:
  2. jcsd
  3. Jul 27, 2005 #2
    you want to start with the Lorentz force law. It states that the vector forces an electric charge will feel from a magnetic and electric field are

    F = q(E + v x B) where E, v, and B are vectors and the x denotes the cross product. Pick any direction for the velocity (say the z direction) and then calculate the vector force. I think the other equaiton you have will just give you a magnitude.
  4. Jul 27, 2005 #3
    thank u so much... that definitely helped...i solved the problem by doing:F=qE F=qvB then (qE)squared +(qvB)squared than i took the square root of that total :)
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