- #1

bolzano95

- 89

- 7

## Homework Statement

Coaxial cable has radius a of copper core and radius b of copper shield. Between there is an isolator with specific resistance ζ. What is the resistance of this cable with length L between the core and the shield?

## Homework Equations

First, I tried to solve this like this:

[tex]R= ζ \cdot \frac{l}{S}[/tex]

In our case the length is dr, and therefore I suppose that the area of this ring is 2πrdr:

[tex]dR= ζ \cdot \frac{dr}{2πrdr}[/tex]

## The Attempt at a Solution

The solution sheet says: [tex]dR= ζ \cdot \frac{dr}{2πrL}[/tex]

I know that something is wrong with my equation, because dr goes away and then I cannot integrate from a to b. But why is in the solution L instead of dr? As I understand problem instruction L= b-a. And therefore L=dr which doesn't make sense to me.