1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Lorentz force - e- in EM field

  1. Apr 9, 2013 #1
    1. The problem statement, all variables and given/known data
    An electron in an electric field E = 3.0x107 ex NC-1 and a magnetic field B = 3.0 ez T has velocity v = 1.0x107 (2ex - ey) ms-1.

    Calculate electromagnetic force on the electron.

    2. Relevant equations
    F = q (E + v X B)
    where q = e- = -1.6x10-19 C

    3. The attempt at a solution
    I have attached a working out, but have difficulty with just one aspect.

    Whilst working out the matrix vXB I have a negative sign where I think a positive sign should be.
    I have attached the working as a pic.
    Could someone show me why I am correct or incorrect.
    Thank you.

    Attached Files:

  2. jcsd
  3. Apr 9, 2013 #2
    Ah! Is this to do with ex X ey = -ey?
    They're orthogonal?
  4. Apr 9, 2013 #3
    The negative sign comes from the definition of the cross product.
    v x B = ex(...) - ey(...) + ez(...)
  5. Apr 9, 2013 #4
    Again, I have to go "Doh!"
    Thank you.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted