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Lorentz Force Law, am i messing up vector algebra?

  1. Nov 6, 2005 #1
    Okay here is my work:
    http://show.imagehosting.us/show/891312/0/nouser_891/T0_-1_891312.jpg
    and here is my calculations part:
    http://img136.imageshack.us/img136/5539/lastscan7qc.jpg
    Problem says:
    14. [HRW7 28.P.008.] An electron has an initial velocity of (14.0 j + 21.0 k) km/s and a constant acceleration of (3.50 10^12 m/s2) i in a region in which uniform electric and magnetic fields are present. If B = (400 µT) i, find the electric field E.
    V/m i + V/m j + V/m k

    I know i'm getting the wrong answer because i tried to submit the i component and it was wrong i got:
    19.88i

    any ideas where i screwed up?
     
  2. jcsd
  3. Nov 6, 2005 #2
    I haven't really done the question here, but from the looks of it you have rounded your values incorrectly. Are you using the full calculator value in your calculation though? If so then it doesn't matter, but if you're using rounded values then your answer might just be out by a little. You're using SI units throughout so you definitely have V/m as your final unit.
     
  4. Nov 6, 2005 #3

    lightgrav

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    last time I checked, electrons had charge negative (-) e !
     
  5. Nov 7, 2005 #4
    so u don't use the magntiude of the charge in that equation?
     
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