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Homework Help: Electric Field question?

  1. Jan 26, 2010 #1
    What is the strength of an electric field that will balance the weight of a 2.5g plastic sphere that has been charged to -2.9nC ?

    I know that F= ma and that E= Kq/r^2 and also that F= Kq1q2/(r^2). I just don't know how to relate an electric field equation using only mass and a charge?
     
  2. jcsd
  3. Jan 26, 2010 #2

    Doc Al

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    Staff: Mentor

    OK. What would 'a' be in this case?
    Those are expressions for the field from a point charge and the force between two point charges. You won't need them here. Hint: If the field is E, and the change is q, what's the electric force on the charge?

    What forces act on the plastic sphere? What's the net force?
     
  4. Jan 26, 2010 #3
    a= acceleration

    and i will need the F=qE equation

    if the sphere is being balanced then the net force will be zero?
     
  5. Jan 27, 2010 #4

    Doc Al

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    Staff: Mentor

    I meant, what would be the value of the acceleration in this case.

    Right. That's the one you need.

    Exactly. What two forces act on the sphere?
     
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