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Homework Help: Minus signs on Voltage and potential energy!

  1. Sep 4, 2008 #1
    Just two quick questions

    1. if you have a positive charge and a negative charge of equal magnitude and you pick a point directly half way between then
    is the electric potential zero but the electric is not?? is that true? why?

    2. if you take an electron and move it from positive to negative terminal is the change in potential energy negative or positive?
    what is the rule for determining if a change in potential energy is positive or negative?

    thank yo u
  2. jcsd
  3. Sep 4, 2008 #2


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    Homework Helper

    Don't understand your question. The electric what is not?

    You mean change in PE of the electron? If so, then ask yourself if moving the electron from positive to negative entails doing work on the electron (ie. going against the field). If it is doing positive work, then the work done on the electron added to its potential energy (by the work-energy theorem).

    EDIT: Ok, it's not called the work-energy theorem here (which seems to apply only to KE), I forgot what the law is called, but it's the one which says that doing work on some system means increasing the system's energy (whether kinetic or potential).
  4. Sep 4, 2008 #3
    Hi Sorry for that.

    for number one I meant to say electric field

    for number 2 yes I mean the change in PE of the electron.
    So because it is a negative charge (electron) and we are going against the field it will be POSITIVE work
    but if it were a positive charge and we are going against the field it will be negative work

    Last edited: Sep 4, 2008
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