# Homework Help: 2011 AP Physics C E&M frq #1 clarification

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1. Apr 4, 2012

### cubejunkies

Problem 1 on last year's normal (not form b) frq for e&m part a asked to use Gauss' law to prove essentially that at any point P within a thin spherical shell of charge density σ = q/A and radius r that the electric field at this ambiguous point P is zero. The solutions for this problem went typically from the surface integral of the dot product of E and dA, and yielding that E(4πr2) = Qenclosed0, and then merely states with words that any explanation relating spherical symmetry to the problem gets a point. I tried doing some long messy integrals but only ended up with E = 2σ/ε0 which is definitely not the answer because although it is independent of the distance from the center of the shell, it's not zero.

Sorry if my question doesnt make sense.

I'm just looking for a more rigorous, thorough explanation for this problem

Thanks!
Anthony

http://apcentral.collegeboard.com/apc/public/repository/ap11_frq_physics_cem.pdf
http://apcentral.collegeboard.com/a..._electricity_magnetism_scoring_guidelines.pdf
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution