# Capacitance of an asymmetrical parallel plate capacitor

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1. Feb 18, 2015

### nickexists

I've been looking all over and to my great surprise have not be able to find an answer to this question.

What is the capacitance between to parallel plates if one plate is larger than the other? For example, the capacitance between a 1" diameter plate and a 4" diameter plate.

Thanks.

2. Feb 18, 2015

### f95toli

The math gets quite tricky when you have situation like that. As a first approximation the capacitance would be nearly the same as for two identical plates (since most of the E-field lines will be perpendicular to the plates). However, if you want to take edge effects into account the calculation becomes tricky and in the "real world" you would probably have to solve this numerically.

3. Feb 18, 2015

### nickexists

Thanks. I am actually interested in how this works out in the real world, do you know more specifically how I would go about solving this numerically?

4. Feb 18, 2015

### zoki85

If the plates are close enough, the capacity will be very close to the capacitor of both plates plates being 1" dia

5. Feb 18, 2015

### jim hardy

A tricky integral over the volume of the E field... i dont know how one would establish outer bound.
See hyperphysics example of a spherical capacitor , for an approach...