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Homework Help: The field Model

  1. Jul 25, 2012 #1
    1. The problem statement, all variables and given/known data

    What are the strength and direction of an electric field that will balance the weight of a 1.0g plastic sphere that has been charged t0 -3nC ?

    2. Relevant equations
    E= F/q

    3. The attempt at a solution

    Newton's laws on the charged sphere

    ƩFnet(y) = F -mg=0
    E = mg/q
    =3x10^6 N/c
    how do i conclude on the direction?
  2. jcsd
  3. Jul 25, 2012 #2

    I like Serena

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    Homework Helper

    Hi Lydia22! :smile:

    You have already used what the direction must be.
    So you only have to make your conclusion explicit.

    In your first line you have ƩFnet(y) = F -mg=0, which is the condition for the sphere to be in balance.
    This implies that the electric force is equal and opposite to the force of gravity.
    Since q is positive, that also holds true for the electric field.
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