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Homework Help: Calculating E/M for Helmholtz Coils -- help please

  1. Oct 23, 2014 #1

    edit: wait... I think the discrepancy is that I calculated Coulombs per kg? and the accepted value I was looking at was in abcoulombs per kg. If that is indeed the case, then my answer is indeed close to the accepted value of 1.76 * 10^11 Coulomb/kg.

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

    I am trying to calculate e/m for data I got from a laboratory experiment with a helmholtz coils. I am not sure if I have bad data, or if I have a mistaken unit somewheres. I am getting 1.96 * 1011 after I average all my e/m together. I should be getting 1.76 * 107

    Am I doing something wrong, or is it my data? I am not going to put all my data up. I will just put some 1 measurement and please tell me if I am using wrong units somewheres.

    2. Relevant equations

    e/m = [PLAIN]http://badger.physics.wisc.edu/lab/manual2/img129.gif2.47 [Broken] x 1012[PLAIN]http://badger.physics.wisc.edu/lab/manual2/img130.gif[PLAIN]http://badger.physics.wisc.edu/lab/manual2/img131.gif[PLAIN]http://badger.physics.wisc.edu/lab/manual2/img132.gif [Broken] coulombs/kg

    3. The attempt at a solution

    my measurement is:

    accelerated voltage = 40 volts
    current for helmholtz coils = 2.46 Amps
    Radius of coil = .33 meters
    there are 72 turns on each coil
    radius of the electron beam = .039 meters

    I get 2.25 * 10^11
    is this what my data gives me, or am I using the formula incorrectly? I should get 10^7
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Oct 28, 2014 #2
    Thanks for the post! Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
  4. Oct 29, 2014 #3
    no worries. I went ahead and went with what I had. It must have been correct, my professor accepted it.
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