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Homework Help: Electron in solenoid

  1. Mar 7, 2012 #1
    1. The problem statement, all variables and given/known data

    A long solenoid has 100 turns/cm and carries a current i. An electron moves within the solenoid in a circle of radius 0.022 cm perpendicular to the axis of the solenoid. The speed of the electron is 0.048c (c is the speed of light).

    2. Relevant equations

    f = m*v^2/r = q*v*B
    B of a solenoid = u*n*I
    where n = number of turns per meter
    u = 4*pi*10^7

    3. The attempt at a solution

    so B = mv/(r*q) = u*n*I
    I = mv/(r*q*u*n)
    I = 5436.9 is not correct
  2. jcsd
  3. Mar 8, 2012 #2


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    Homework Helper

    your working looks fine to me... But I got a different value for the current when I plugged the numbers in. Maybe that's where the problem is.
  4. Mar 8, 2012 #3
    I was using the mass of a proton instead of an electron. replugged the numbers, and it works now!
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