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Homework Help: Calculating e/m ratio

  1. Jan 19, 2009 #1
    1. The problem statement, all variables and given/known data

    I'm trying to calculate the charge ratio of e/m, I've plotted the given data points to get a straight line graph with a gradient of 0.848.



    2. Relevant equations

    I know that I can calulcate the charge ratio of e/m by using
    e/m = (4.49*10^8 * gradient^2)/volts

    where volts = 3000.

    3. The attempt at a solution

    When I plug the numbers in I get a value of 107625 which is nowhere near the given book value of e/m 1.7*10^11 Ckg^-1

    I think that I'm doing something in the wrong units as I need to get the answer in C/kg^-1, but I can't see where I'm going wrong.

    Any pointers would be much appreciated
     
  2. jcsd
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