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When is electric potential negative and when is it positive?

  1. Mar 1, 2014 #1
    1. The problem statement, all variables and given/known data

    When is electric potential negative and when is it positive?

    2. Relevant equations

    V=Es

    3. The attempt at a solution

    I first thought that when you are moving in the same direction as the electric field the electric potential will be a positive value.
    However I across a problem in which you are moving a charge in the positive x direction the electric field is also in the positive x direction, and yet the answer is a negative value.

    Can someone please help and explain this to me in easy terms? I searched for an answer, but I am still confused.

    Thank you!
     
  2. jcsd
  3. Mar 1, 2014 #2
    Be careful with the term "potential". Potential really involves a change in potential difference. So the potential you measure for a certain object depends on where the potential is defined to be zero -- the potential of the object is really a change in the potential from this reference point to the object's location. In this case, the potential and the potential difference have the same value, so you can just use the absolute potential instead.


    So really the potential of something depends on where potential is defined to be zero. With your idea of moving in the same direction as the electric field (look at your equation though -- there should be a negative in there), the potential is going to decrease if you follow a field line, but it won't necessarily be negative or positive.

    If you have potential defined at infinity (as it typically is), then the potential of something will be positive if it has positive charge (because following a field line would lead outward toward zero, so you have to start at something positive), and the potential of something will be negative if it has negative charge (by the same idea).
     
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