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Homework Help: Distance of ions from photographic plate

  1. Feb 25, 2010 #1
    1. The problem statement, all variables and given/known data
    How far would the spot on the photographic plate be from the entry point for each ion, assuming that each ion completes half an orbit?
    I am given three ions, N+subscript2, O+subscript2, NO+
    They have atomic masses of N=14.0031amu and O=15.9949amu.
    I am given the magnetic field strength=8.5MN/C
    The magnetic field is uniform and perpendicular to the velocity.

    2. Relevant equations

    I tried to use R=mvc/ qB

    q is the charge, m=mass, v=speed, c=speed of light, B= magnetic field strength

    3. The attempt at a solution

    I tried simply substituting these in and using the standard 1.60*10^-19C for the charge. For the mass i just took the atomic mass, multiplied it by the subscript of two for the first two and then converted it to kg.
    I got it wrong.. and i can't tell why.
    If i could just figure out what i did i'm pretty sure it's the mass or the charge that is incorrect but i have not had chemistry in quite awhile and can't figure it out....

    Thanks for all your help in advance!
  2. jcsd
  3. Feb 25, 2010 #2


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    Homework Helper

    Think about it more. Do the ions really hit the plate 1 radius away from their starting position?
  4. Feb 26, 2010 #3
    No. I think it's 2R now. Thank you... I'm not sure how i overlooked that.
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