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Homework Help: Potentials and voltages

  1. Jan 8, 2007 #1
    1. The problem statement, all variables and given/known data

    Point X is 0.25m away from a point charge of +4.7 E -8 C, point Y is 0.65m away. What is the potential of point X with respect to point Y?

    2. Relevant equations
    delta Ep=delta Ek
    V=delta Ep/Q
    delta Ep=QV
    Ep=kQQ/d

    3. The attempt at a solution

    delta Ep = -Ep1
    W=QV
    W=kQQ(1/d-1/d)
    QV=kQQ(1/.25-1/.65)
    V=(9E9)(4.7E-8 C)(2.4615)
    V=1041 V

    I don't get one thing when it says with respect to Y, you put the distance of Y as d2 right? But then wouldn't you get a negative answer when it should be positive?
     
  2. jcsd
  3. Jan 8, 2007 #2

    Hootenanny

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    Staff Emeritus
    Science Advisor
    Gold Member

    What you have done here is all correct, except the answer. You've just punched the numbers into your calculator wrong.
    The potential of x wrt to y means exactly what you have done there. In other words calculate the potential difference between points x and y like this; [itex]V_{xy} = V_{y}-V_{x}[/itex], which would lead to a positive answer.
     
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