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Electric Potential problem

  1. Nov 4, 2014 #1
    • Use of the homework template is mandatory in the homework forums.
    The electric field at the origin is along the positive x axis. A small circle is drawn with the center at the origin cutting the axes at points A, B, C, and D having coordinates (a,0), (0,a), (-a,0), (0,-a), respectively. Out of the points on the periphery of the circle, the potential is minimum at _______?
    (a) A (b) B (c) C (d) D

    After drawing the diagram, I see that the electric field is directed towards the right along the x-axis (towards A). However, electric potential = KQ/r, and here Q and r are constant for all four points. I don't see how any point could have "minimum" potential.
     
  2. jcsd
  3. Nov 4, 2014 #2

    BvU

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    Hello Epic, welcome to PF :)

    Did you notice the template ? Better use it.

    However:
    Your electric potential expression isn't applicable here. There is no mention of Q !

    You want to make use of a different relationship between E and V.
    In the template, there is room for such equations under 2) relevant equations.
     
  4. Nov 4, 2014 #3
    1. The problem statement, all variables and given/known data
    The electric field at the origin is along the positive x axis. A small circle is drawn with the center at the origin cutting the axes at points A, B, C, and D having coordinates (a,0), (0,a), (-a,0), (0,-a), respectively. Out of the points on the periphery of the circle, the potential is minimum at _______?
    (a) A (b) B (c) C (d) D

    2. Relevant equations
    V = -E dr

    3. The attempt at a solution
    After drawing the diagram, I see that the electric field is directed towards the right along the x-axis (towards A). But how will integrating the above equation give me the "minimum" potential necessary?
    Thanks for the help
     
  5. Nov 5, 2014 #4

    BvU

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    Much better !
    Actually, it's ##{\bf d}V = -\vec E\cdot d\vec r\,##. You integrate and get ##\Delta V##, which happens to be just the one you are after !
     
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