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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.
     
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