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Homework Help: Electron Through a Magnetic Field

  1. Dec 15, 2012 #1
    1. The problem statement, all variables and given/known data
    An electron travelling North with a speed of 8.9x10^6 m/s enters a magnetic field of strength 0.069 T pointing East.

    In what plane (upward and North-South, upward and East-West, or horizontal) does the electron's orbit lie?

    2. Relevant equations

    3. The attempt at a solution

    Since it's an electron, I would normally use the left hand rule to determine the direction of the force acting on the electron which would be upwards. I just don't understand my options. Since it's already travelling along the North-South, would the magnetic force cause the electron to orbit vertically along the North-South since the force is always centripetal? That's what I would guess, but I'm not very confident with that answer.
  2. jcsd
  3. Dec 15, 2012 #2


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    Staff: Mentor

    Your analysis looks okay. As you say, the Lorentz force on the electron will (initially) point vertically upwards. Since centripetal force points towards the center of the orbit, the center lies in a vertical plane containing (or at least parallel to) the N/S axis.
  4. Dec 15, 2012 #3
    Thank you for confirming gneill!
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