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Homework Help: Magnetic fields

  1. Apr 4, 2005 #1
    an electron with velocity u = (3,12,-4) x 10^5 experiences no net force at a point in a magnetic field B = ((10,20,30)/ Find E at that point.

    I found the magnetic force by u cross B. Set Fe equal to Fm. Divided by q to get E = u cross B. but im not getting the same answer as the back of the book. just need a confirmation.
    im getting E = (4.4 x 10^7, -1.3 x 10^7, -6 x 10^6)
    the book has the same number for the x direction, its just 4400.
     
    Last edited: Apr 4, 2005
  2. jcsd
  3. Apr 4, 2005 #2

    dextercioby

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    [tex] m\vec{0}=q_{e}\left(\vec{E}+\vec{u}\times\vec{B}\right) [/tex]

    That's all u need.Use it propertly.

    Daniel.
     
  4. Apr 4, 2005 #3
    I came up with the same numbers. It's just a simple cross product, the answers in the book must be wrong.
     
  5. Apr 4, 2005 #4
    Signs should be reversed though, from bringing E to the other side of the Lorentz force equation.
     
  6. Apr 4, 2005 #5

    dextercioby

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    Are u sure that [itex] E_{x} [/itex] is not [itex]-4.4\cdot 10^{7} \frac{V}{m} [/itex]...?

    Daniel.
     
    Last edited: Apr 4, 2005
  7. Apr 4, 2005 #6
    what is that formula for?
     
  8. Apr 4, 2005 #7

    dextercioby

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    What formula?

    Daniel.
     
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