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Force on an electron in a magnetic field

  1. Jul 21, 2017 #1
    1. The problem statement, all variables and given/known data
    What is the force on an electron with a velocity v = (2i – 3j) Mms-1 in a magnetic field B = (0.8i +
    0.6j – 0.4k) T

    2. Relevant equations
    F=qvBsinθ

    3. The attempt at a solution
    using cross product I got: (1.92i + 1.28j + 5.77k)10^-13 N which is the listed correct answer.

    My question is since this was an electron, why the value wasn't negative 1.92i, etc. Wouldn't the charge have contributed to the direction? Can someone please explain this to me?
    Thanks
     
  2. jcsd
  3. Jul 21, 2017 #2

    berkeman

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    Staff: Mentor

    The sign of q in the vector qvB contributes to the sign of the cross product answer...Can you show your work including the calculation of the cross product?
     
  4. Jul 21, 2017 #3
    sure solution.jpg
     
  5. Jul 21, 2017 #4

    berkeman

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    Staff: Mentor

    Yeah, your work and your answer with the "-" signs looks right to me. You are saying that the "+" answer is listed as the correct answer?
     
  6. Jul 21, 2017 #5
    Yes, but the professor has been known to make mistakes.
     
  7. Jul 21, 2017 #6

    berkeman

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    Staff: Mentor

    Does he/she have office hours before this is due? Show them your work and ask politely if you've missed anything...?
     
  8. Jul 21, 2017 #7
    I have done just that. Hopefully I can get a clarification. It's very difficult to learn magnetism while correcting typos!
    Thank you!
     
  9. Jul 21, 2017 #8

    berkeman

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    Staff: Mentor

    You're welcome. Just keep doing the math, and you should be fine. :smile:
     
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