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Homework Help: Electric Potential between two charges of equal magnitude

  1. Apr 6, 2014 #1
    1. The problem statement, all variables and given/known data
    Two charges of equal magnitude Q are held a distance d apart. Consider only points on the line passing through both charges.

    If the two charges have the same sign, find the location of all points (if there are any) at which the potential (relative to infinity) is zero.

    a) Midway between the charges
    b) At the points, where the charges are
    c) There are no such points

    2. Relevant equations
    V = k(Q/r)

    3. The attempt at a solution
    I know the answer is not a. But because of the "relative to infinity" statement, I'm not sure about b or c.

    For b, the equation would look like: V = k(Q/0) + k(Q/d). I don't know what to do with the division by 0.

    I'm inclined to go with c, but I would like some support please.
  2. jcsd
  3. Apr 6, 2014 #2


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    Staff Emeritus
    Science Advisor
    Homework Helper

    Since the potential approaches infinity at the charge, one simple way to think about the division by 0 is that it is equivalent to infinity.

    Even better is to make a graph of the potential, and then look at how the graph behaves in between the charges. You can either hand-sketch a graph, use a graphing calculator if you have one, or perhaps use Microsoft Excel, if your computer has it, to make the graph. You can use anything you want for Q and d, but I suggest trying Q=1 nC (that's 1×10-9 C) and d=1 meter for convenience.
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