1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Not sure why this is true

  1. Apr 7, 2008 #1
    In a uniformly charged sphere, why inside the sphere is [tex] \bold{E} = \frac{1}{4 \pi \epsilon_{0}} \frac{q}{R^3} r \bold{\hat{r}} [/tex]?

    I don't see how this follows from Gauss's law.
  2. jcsd
  3. Apr 7, 2008 #2
    The ratio of the charges between the inner sphere (Q') and the outer sphere (Q) is equal to the ratio of the volume between the inner and outer spheres.

    [tex]\frac{\frac{4}{3}\pi r^3}{\frac{4}{3}\pi R^3}=\frac{Q'}{Q}[/tex]

    Thus: [tex]Q' = Q\frac{r^3}{R^3}[/tex]

    Now use Gauss's Law to find the electric field inside the inner sphere.
  4. Apr 7, 2008 #3
    Just to clarify what Snazzy said, the inner sphere is your Gaussian Surface.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook