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Homework Help: Calculating Electric Potential Differences

  1. Feb 18, 2010 #1
    1. The problem statement, all variables and given/known data
    When an electron moves from A to B along an electric field line in the figure below, the electric field does 2.00 10-19 J of work on it.

    What are the electric potential differences:
    (a) VB - VA

    (b) VC - VA

    (c) VC - VB

    2. Relevant equations
    Ok so I know that the equation to use in this case is that of, [tex]\Delta[/tex]V = [tex]\frac{-W}{q}[/tex]

    3. The attempt at a solution
    I understand how to choose the equation I've chosen and how to get the right answer. What I don't understand is why the answers to (a) and (b) aren't negative when the equation shows that they should. Can anyone help?
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Feb 18, 2010 #2


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    Homework Helper
    Gold Member

    I don't have all the problem details (not enough to actually work out the problem). But allow me to speculate: Forgot the negative charge of the electron maybe? :wink: There's enough information for me to do the first part.

    The given wording was "When an electron moves from A to B [...] the electric field does [positive value] J of work on it."

    If the above statement applied to a test charge it means the V(A) is greater than V(B). But we're not dealing with a positive test charge. We are dealing with a negative electron :cool:. So given the negative charge, the statement implies, V(B) is greater than V(a). Therefore,

    V(B) - V(A) is positive.
    Last edited: Feb 18, 2010
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