Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Electric Field/Potential Of A Sphere

  1. Sep 12, 2008 #1
    Ey all

    Im a little confussed with electric fields and potential. My text book says one thing and my tutor has said the opposite*, so im not sure what to belive.

    If we have a "uniformly" charged necleus(we can model as a uniformly charged sphere) thus the charge(protons) are spread throughout the whole volume of the sphere not just the surface** (only at surface when all points in the sphere are in electrostatic equilibrium which isnt stated*)

    Therefore the electric field would be
    R- radius of necleus, r- radius,
    Eoutside necleus = (1/(4*pi*e0))*(Q/r2), When r>R
    Einside necleus = (1/(4*pi*e0))*(Q*r/R3),When r<R

    My totor said that E=0 inside the nucleus, im hoping i only copied down what she said wrong :S, if someone can confirm please. If the formula are correct therefore the elctric field increases as we get closer to the center of the nucleus

    Electrostatic potential,(doesnt state that neucleus is in electrostatic equilibrium so im unsure why they dont simply ask for potential* anyway, if someone can explain i would appreciate it, from what ive read they are the same)
    Voutside necleus = (1/(4*pi*e0))*(Q/r) When r>R
    Vinside necleus = (1/(4*pi*e0))*(Q/R) When r<R
    Assuming the formula are correct therefore the potential inside the nucleus is constant? and decreases by 1/r outside the nucleus,

    Cheers Trent
    Last edited: Sep 12, 2008
  2. jcsd
  3. Sep 12, 2008 #2
    The more i look, the more convinced i am that there is a electric field in a sphere with charge uniformly distributed, anyone else know for sure?
  4. Sep 12, 2008 #3


    User Avatar
    Homework Helper

    There's no reason why the E-field in the sphere should be zero since the charge is uniformly distributed throughout the volume. A similar setup for this would be an insulator sphere which has a uniform volume charge density. Gauss law and symmetry would tell you that the E-field inside is non-zero.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook