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Homework Help: Vector sum of magnetic and electronic forces

  1. Jun 8, 2009 #1
    1. The problem statement, all variables and given/known data

    A long, straight horizontal wire carries a current of 2.50 A directed toward the right. An electron is traveling in the vicinity of this wire.

    A)At the instant the electron is 4.50 cm above the wire and moving with a speed of 6.00×10^4 m/s directly toward it.
    What is the magnitude of the force?

    B)What would be the magnitude of the magnetic force if the electron were instead moving parallel to the wire in the same direction as the current?

    2. Relevant equations

    3. The attempt at a solution
    I tried to find the vector sum of two forces; the electron toward the wire and the magnetic force. But how can I determine the force of electron by only knowing its final velocity?
    Or am I on the wrong track?
  2. jcsd
  3. Jun 8, 2009 #2
    Hi there,

    You are quite on the wrong track. You are only asked to find the interaction created by the current in the wire on the electron moving next to it, and not its acceleration. There is no vector sum in this case.

  4. Jun 8, 2009 #3
    Some guiding questions that may help:

    1. What is the magnitude and direction of the magnetic field at a point 4.5 cm above the wire?

    2. What formula is used to calculate the force acting on a moving charge in a magnetic field?
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