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Homework Help: Maximum speed of an electron in an ideal solenoid

  1. Apr 1, 2012 #1
    1. The problem statement, all variables and given/known data

    A particular ideal solenoid has 1200 turns/m, a radius of 10 cm, and a current of 4.0 A. An electron is fired from the axis of the solenoid in a direction perpendicular to the axis. What is the maximum speed the electron can have if it is not run into the side of the solenoid?

    I know the answer is 5.3 ×10^7 m/s but I have no idea how to arrive there... Any help would be great. Thanks.

    2. Relevant equations

    u=4pi*10^-7 T m/A



    3. The attempt at a solution

    I just plugged in the values to get B which ended up being .006032T and than used r=(mv)/(qB) to get v.... but that didn't seem to work.
  2. jcsd
  3. Apr 1, 2012 #2


    User Avatar

    Staff: Mentor

    Don't confuse the radius of the solenoid with the radius of curvature of the electron's trajectory. The electron's trajectory will describe a circle. What's its maximum diameter?
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