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Homework Help: Potential Difference Confusion

  1. Nov 16, 2005 #1
    There seems to be two different uses of potential difference that either contradict each other, or at the very least make it very confusing. Let me write the three different forms:

    Definition: Vf-Vi= -E*d
    Differential: dV=-E*dr (Vi=0)
    Point Charge: V=E*r (Vf=0)

    What is with the different reference potentials (Vi,Vf=0)? Can someone please make sense out of this.

    Edit: I avoided writing integrals above because I don't how to use latex, and the book I'm studying is Halliday, Resnik.
    Last edited: Nov 16, 2005
  2. jcsd
  3. Nov 16, 2005 #2


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    Here is a nice discussion of potential energy. It is really the change in potential energy that matters.


    Gravitational potential energy - http://hyperphysics.phy-astr.gsu.edu/hbase/gpot.html#mgh

    Electric potential energy - http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elepe.html#c1

    Reference potential - potentials are relative!

    ref Hyperphysics

    Read also the third plate in the link on electric potential - Potential Reference at Infinity.
  4. Nov 17, 2005 #3
    Ok, so you Vf & Vi are values of potential. So if you substract them, you get the difference in potential between them.

    Your second is just substituting 0 into your first equation.

    Your third equation is not potential difference. It is a value of electric potential at a distance r from a point charge (It is the energy required to bring a unit charge of identical polarity from infinity to the distance r from the point source; thats the way I think about it).

    Does this help you?

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