# Capacitance of a cylinder containing an infinite number of cylinders

1. May 3, 2005

### IanS

I am a struggling physiology PhD student and would very much appreciate some help...

I need an expression for the capacitance of a cylinder (of finite radius and length) containing an infinite number of infinitely thin cylinders.

Any help would be greatly appreciated!

Many thanks,
-Ian

2. May 3, 2005

### Meir Achuz

Your question is poorly posed. Capacitance is defined as the ratio of the charges on two conductors (+Q on one and -Q on the other) to the voltage (V) between them,
so C=Q/V. With an infinite number, what do you mean by capacitance?
Is the outer cylinder of finite length open or closed at the ends?

3. May 3, 2005

### Chi Meson

Is the outside cylinder fully closed (that is, closed off at both ends)? If it is, then it does not matter what is inside it (I'm 90% sure of that, but someone correct me please).
Is there any separation between the outside cylinder and the inner ones? If not, then it would be identical to a solid cylinder, which would be identical (in capacitance) to a cylindrical shell.

Otherwise, the problem implies an infinitessimal distance between layers of a capacitor, which implies a capacitance that approaches infinity.