1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How do I calculate the electric potential

  1. Apr 22, 2007 #1
    How do I calculate the electric potential "V" of a point charge "q" at radius "r" if I am told that the electrical potential is zero at a distance "d" other than infinity? I believe that there is some arbitrary constant that must be found but I don't know if, where, or how that fits in.

    Formulas I know:
    V=U/Q (where U is the potential energy)

    Thank you very much if you can help!
  2. jcsd
  3. Apr 22, 2007 #2
    If V at r = (Kq)/r, and at infinity V = 0. What is the difference ? Ask yourself why at infinity, the V = zero.
    Last edited: Apr 22, 2007
  4. Apr 22, 2007 #3
    The V=0 at infinity because as r goes to infinity, the function becomes infinitely small.

    But what if V=0 at 1meter? Then how would I find V at .5 meters? for some reason the equation V=K(q/r) doesn't work by itself in this case. The only way I can reconcile this is if there is some other part to the equation that we leave out because V=0 is usually at infinity. Any ideas?!
  5. Apr 22, 2007 #4
    Is this a book question or are you having a problem with a concept? Where did you get V = 0 at 1, at r =1 ? Doesn't V = 0 at r =1 a contradiction if the equation is Kq/r? wouldn't V = kq at 1?
    Last edited: Apr 22, 2007
  6. Apr 22, 2007 #5
    Exactly my problem. My professor assigned a few problems where V=0 at different distances (not infinity). Supposedly it doesn't matter where you set the zero of electric potential (just like it really doesn't matter where you choose the zero of gravitational potential), I just can't figure out how the equation should be set up.
  7. Apr 22, 2007 #6
    This is how you find teh potential due to a uniformaly charged sphere, or simply a charge :

    DV=change in V= potential difference=V2-V1=(Kq)/r2 - (Kq)/r1
    = (Kq)[1/r2 - 1/r1]
    at r1= infinity , V1= 0 Which is how you get a voltage value at a distance outside a charge, you assume r1 is infinate distance. If you really say your teacher said you can get a zero voltage. My oh my:frown:
    Last edited: Apr 22, 2007
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: How do I calculate the electric potential