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Electric force acting on an electron

  1. Feb 26, 2012 #1
    An elctron moving through an electric field experiences an acceleration of 5.4 x 10^3 m/s^2. Find the electric force acting on the electron.

    I think the equation F=ma may be used and maybe E=F/qsubo Do I need to use the fundamental charge to find an answer? using the fundamental charge of 1.60x10^-19.

    My attempt at a solution is:
    F=86.4x10^-16 N/C

    is that correct? The fundamental charge was not given in the question. Is this even the correct way to find the solution?
  2. jcsd
  3. Feb 26, 2012 #2


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    You have multiplied an acceleration by a charge and claimed the answer has unit N/C - and I think your answer should not be 86.4 x 10-16 perhaps just 8.64 x 10-16 - not that that is correct.

    For a start, you were trying to find a force - so the units if the answer would be Newtons alone.

    I don't think you need the fundamental charge, but I do think you need the electron mass.
  4. Feb 26, 2012 #3
    Well, I'm finding the Electric Force which could also be E=F/q. Although, without any mass, I can't solve for F and put it into the equation. You were correct with the 8.64 x 10^-16, I simply calculated it incorrectly.

    So, is the way I went about solving this equation correct?
  5. Feb 26, 2012 #4


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    Not really. E is the Electric Field Strength. Did you know the size of the Electric Field Strength?

    F = ma seems a much better idea.
  6. Feb 26, 2012 #5
    I do not know the size of the Electric Field strength. :/ that's why I resorted to the fundamental charge of 1.60 x 10^-19.
  7. Feb 26, 2012 #6


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    I was suggesting that trying to use any formula that involves the Electric Field Strength (E) is not a good idea for the exact reason that you don't know its value.

    Perhaps you were distracted by the word Electric in the original question.

    An electron may accelerate because is is near the Earth [we could expect 9.8 at best] due the effects of a Gravitational Field.
    It may accelerate because it is placed in an electric field.
    It may accelerate because it is moving through a magnetic field.

    The reason it accelerates in this case is presumably because of an appropriately sized Electric field; but form there F = ma is all you need.
  8. Feb 26, 2012 #7
    OH!!! That makes so much more sense! Thank you so much for explaining that! That was so helpful! I really appreciate it! :)
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