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Homework Help: What is the magnitude of the electric field where the electric potential is zero?

  1. Jul 14, 2011 #1
    1. The problem statement, all variables and given/known data

    A -14.3 nC point charge and a +24.9 nC point charge are 17.4 cm apart on the x-axis. What is the magnitude of the electric field at the two points on the x-axis where the electric potential is zero?

    2. Relevant equations

    V = kq/r
    E = kq/r^2

    3. The attempt at a solution

    Since the potential = 0,

    q1 = -14.3 nC, q2 = 24.9 nC

    kq1/(r+0.174) = kq2/r

    But this gives me one negative value for r, whereas I need two values.
  2. jcsd
  3. Jul 14, 2011 #2
    Electric potential is a scalar.
  4. Jul 14, 2011 #3
    since net potential is zero then

    Potential due to q1 + potential due to q2=0

    means equation is

    kq1/(r+0.174) + kq2/r = 0 ; {not kq1/(r+0.174) = kq2/r}

    this will give two values of r one negative and one positive
  5. Jul 16, 2011 #4
    I figured it out, thank you!
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