# Concentric Spheres Capacitance Question- How to use area

1. Nov 3, 2008

### swooshfactory

1. The problem statement, all variables and given/known data

I am trying to solve a question where I have three concentric metal shells at different radii. I am treating them as two capacitors in series. I would like to use the formula C= enot*area/distance between capacitors, but I have a few questions.

2. Relevant equations

(in next section)

3. The attempt at a solution

1. Which area would I use when computing the capacitance for between shells? I assume the smaller one, because I assume that if you put a small electrode over a larger electrode, the capacitor would only exist in the area between, making the smaller area the area to use.
2. Does this equation assume equal charge? No charge is used in the formula. However, the other formula I know for capacitance, C=Q/deltaV, would assume equal charge over both. Is this relevant for this problem?

Thanks for any help.

2. Nov 3, 2008

### alphysicist

HI swooshfactory,

This is the capacitance formula for a parallel-plate capacitor; a spherical capacitor would have a different formula. Once you find that formula (it should be in your textbook) you'll be able to answer your questions.