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Homework Help: Vector evaluation & Lorentz force 02

  1. Oct 10, 2012 #1
    1. The problem statement, all variables and given/known data
    An electron in electric & magnetic fields;
    E = 3.0x107 ex NC-1
    B = 3.0 ez T
    has velocity
    v = 1.0x10^7 (2ex-ey)

    Calculate em force on the electron.

    2. Relevant equations
    I'm using the Lorentz force law here.
    F = q(E + v X B)

    I have an example solution using vectors to evaluate direction

    | ex_______ey_______ez |
    | 2.0x107_ 1.0x107 __ 0 |
    | 0_______0________3.0 |

    3. The attempt at a solution
    I think this has been posted as the solution to vXB,but then why is the E value 3.0 T there???

    Could someone please ecplain why this is.
    Last edited: Oct 10, 2012
  2. jcsd
  3. Oct 10, 2012 #2


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    3.0 T is the B value, not the E value.
  4. Oct 10, 2012 #3
    Oops, a typo, yes, but why is it there, how does it relate to the Lorentz law & is the solution

    Final calculation 9.6x10-12 N

    I seem to not be able to attach workings in a picture file, sorry.
  5. Oct 10, 2012 #4


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    The determinant will give you the cross product of v and B. The result of the determinant will be a vector. You then need to add the vector E to v x B and finally multiply by q.
  6. Oct 10, 2012 #5
    vXB = ex (3.0x107 - 0) + ey (-6.0x107 - 0) + ez (0)

    q(vXB)= -e (3.0x107 ex + (-3.0x107 ex - 6.0x107 ey) + 6.0x107 * 1.6x10-19 ey) N

    F = 9.6x10-12 ey N
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