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## Homework Statement

I have two coplanar electrodes (180 deg between them) and one of them is under voltage causing circular electric field between them. The target is to calculate the capacitance.

## Homework Equations

Using the capacitance equation C = [tex]\frac{\epsilon_{0}A}{l}[/tex]

I say that A = bdx and l = [tex]\pi[/tex]r

b - is out of plane length of the electrodes

## The Attempt at a Solution

I'm integrating the equation from R1 to R2 (coordinates of electrode on x axis)

but I have to substitute dx with something else - x = rCos[tex]\theta[/tex] so that

dx = cos([tex]\theta[/tex])dr

so the solution is C= [tex]\frac{\epsilon_{0}bCos\theta}{\pi}ln\left(\frac{R2}{R1}\right)[/tex]

Am I doing it rigth?