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EMF homework help

  1. Jan 11, 2010 #1
    A charge Q at a vertex of a square and another Q on the opposite corner of the square and other two charges q each of the other vertices. If the force eletrogmanetica on Q is null which the value of Q in terms of q? There is a q such that the resultant force on 4 charges is zero?

    My attemp

    F = (K.Q.Q)/r^2 + (K.Q.q)/r^2
    F = 0
    KQ^2 + KQq = 0
    Q(KQ + kq) = 0
    Q = - q

    If q = 0 the resultant force is 0

    I correct ?
     
  2. jcsd
  3. Jan 11, 2010 #2

    rl.bhat

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    Re: Emf

    If the side of the square is r, the length of the diagonal is .......?
    At Q three forces are acting. How are they related to get net zero force?
     
  4. Jan 12, 2010 #3
    Re: Emf

    This is my doubt
     
  5. Jan 12, 2010 #4

    rl.bhat

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    Re: Emf

    To get net zero force on Q, Q and q must have opposite sign.
    On charge Q, one repulsive force between Q and Q, and two attractive forces between Q and q are acting. What is the distance between Q and Q?
    Equate the resultant force of two attractive with the repulsive force to find the relation between Q and q.
     
  6. Jan 12, 2010 #5
    Re: Emf

    Yes I find Q = -q is correct ?
     
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