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Need Help on Electric Potential

  1. Oct 10, 2011 #1

    So I pretty much don't understand why certain concepts work when dealing with electric potential.

    Suppose we have an infinite plane with some positive charge density, and the magnitude of the E field at an distance z from the plane is defined as E = (σ)/(2ε) (so the field is uniform and the force exerted on any test charge is always the same, regardless of distance).

    If we place a positive charge near the surface of the plane, it will have high potential energy and move in the direction towards lower potential energy and lower electric potential.

    Now, if we place an electron at some arbitrary distance above the plane, it will move towards the plane. So in theory, it will be moving towards lower potential energy (this I understand) and higher electric potential (this I do not understand at all).

    How can it be moving towards higher electric potential when the potential energy is decreasing the closer it gets to the plane? I understand how it works with a positive charge, but not with a negative test charge.

    And I know that in general, the rule is that electrons move toward lower potential energy and higher electric potential, but I want to understand why. The idea with the electron seems so counterintuitive to me.

    Any help is appreciated. Thanks.
  2. jcsd
  3. Oct 10, 2011 #2


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    Homework Helper

    Although the potential is postive from a positive source, the potential energy is negative for an electron in a field from a positive source. In this case "lower" potential energy means a more negative value.
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