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Homework Help: Force of an electron with magnetic and electric fields and velocity

  1. Mar 22, 2009 #1
    1. The problem statement, all variables and given/known data
    An electron travels with v= 5.90(10)^{6} i through a point in space where E=<2.30 (10)^{5} i, -2.30(10)^{5} j> and B = <-0.200 k>

    2. Relevant equations
    F=q(E+(v x B)

    3. The attempt at a solution
    I did q of the electron equals 1.6(10)^-19 the with v x B = -.2k (5.9)10^6 i= -1.18(10)^6 j getting 1.6(10)^-19<2.3(10)^5 i, -2.3(10)^5 j + -1.18(10)^6 j> = <3.68(10)^-13 i , -1.41(10)^-13>
  2. jcsd
  3. Mar 22, 2009 #2


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    Homework Helper

    Looks like it's OK.

    I would prefer for clarity and of course the opportunity to minimize future problems to have expressed your X product a little more rigorously.

    More like <5.9*106 i> X <-.2 k> = <-1.18*106 j> just to keep track of where things came from.
  4. Mar 22, 2009 #3
    Alright i will take that into account on future questions...and i guess i should have clarified that masteringphysics.com said i was incorrect and that the correct answer was <-3.68E-14, -1.52E-13> so i'm wondering what they did to get there.
  5. Mar 23, 2009 #4


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    Sorry, I scanned it and didn't calculate it out. I thought the X product was OK. But I had the axes reversed when I did the right hand rule.
    I think on closer inspection it's <i> X <-k> = <+j>, not <-j>.

    So try ...
    -1.6*10-19*(2.3*105 i, (11.8 - 2.3)*105 j)
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