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Homework Help: At what point on the x-axis is the Electric Potential zero?

  1. Feb 19, 2012 #1
    1. The problem statement, all variables and given/known data
    A 13.0nC charge is at x = 0cm and a -1.1nC charge is at 6cm. At what point or points on the x-axis is the electric potential zero?

    Let X0 be a position on the x-axis
    Let V1 be the electrical potential at a point due to the 13nC charge
    Let V2 be the electrical potential at a point due to the -1.1nC charge
    2. Relevant equations

    V=k(q)*(1/r); k = Coulomb's constant, q = source charge for which at distance 'r' away, the electrical potential is V volts.

    3. The attempt at a solution
    There are three possible positions for which the electrical potential is 0:
    1) To the left of the 13nC charge
    2) Between 13nC charge and -1.1nC charge
    3) To the right of the -1.1nC charge

    For 1), I took the net voltage: V1 + V2 = 0 which is:
    K(13E-9)*(X0) + K(-1.1E-9)*(X0) = 0, respectively. Simplifying the sum of two fractional terms, I only needed to find the X0 that would make the numerator 0 and thus obtain the X0 for which net Voltage is 0.

    I applied similar calculation procedures for 2) and 3). My results were that X0 = -.0655m, .05532m, .07109m, 1) to 3) respectively.

    Attached is a diagram of the problem solving approach I took.

    Attached Files:

  2. jcsd
  3. Feb 20, 2012 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    Welcome to Physics Forums.
    I'm a little confused by what you did here. It's not clear what X0 is, and I don't see any fractional terms in your equation -- though I agree that there should be.

    Also, for the electric potential, it is not necessary to break the solution process up into three regions. Unlike the electric field, the potential does not "flip sign" when going from one side of a point charge to the other. So you can just set
    V1 + V2 = 0​
    and solve for all x everywhere at once.

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