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Electric potential and electric field

  1. Feb 7, 2008 #1
    [SOLVED] Electric potential and electric field

    1. The problem statement, all variables and given/known data

    A - 10.0 nC point charge and a + 20.0nC point charge are 15 cm apart on the x-axis.
    What is the magnitude of the electric field at the point on the x-axis, between the charges, where the electric potential is zero?

    2. Relevant equations
    sumE = E(of -10) + E (of 20)
    E = kq/r^2
    SumV = V(-10) +V(20)
    V = kq/r


    3. The attempt at a solution

    let the distance at which V = 0 between the charge be x

    SumV = V(-10) +V(20) = 0
    k { (-10 *10^-9/0.15 - x) + (20 *10^-9/ x)} = 0
    solve for x
    x = 0.1
    0.15 - x = 0.05

    SumE = E(-10) +E(20)
    k { (-10 *10^-9/(0.15 - x)^2) + (20 *10^-9/ (x)^2)} = SumE
    substitute x = 0.1
    Sum E= 18000 V

    i don't think this is the right answer
    i think i am doing something wrong
     
  2. jcsd
  3. Feb 8, 2008 #2

    rl.bhat

    User Avatar
    Homework Helper

    The directions of the electric field due to two charges is the same. So the net field is the sum of the absolute values of the two fields.
     
  4. Feb 8, 2008 #3
    thank you
     
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