(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Since this was on the test, I won't be able to type out the question verbatim, but here it goes:

You have a plastic sphere with charge equally distributed through out the sphere. The radius of the sphere is a. The energy stored in the total sphere is E0 (not to be confused with electric field). Find the fraction of the total energy from r=0 to r=a/2 (half the radius).

2. Relevant equations

energydensity*volume = energy

3. The attempt at a solution

I simply put a ratio of the two energies, so E(small)/E0. Since charge is equally spread throughout the sphere, I figured that the energy densities would cancel out, leaving the volume(small)/volume(big). Dividing out gives (1/8)E0.

However, this seems unreasonably easy, and I think I'm missing something very important. Did I do it correctly, or am I forgetting something?

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Energy density test question

**Physics Forums | Science Articles, Homework Help, Discussion**