- #1

fluidistic

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## Homework Statement

The picture describes the situation. I want to find the electric field at point P.

The charged part is a part of an annulus with interior radius a and exterior radius b.

## Homework Equations

None given.

## The Attempt at a Solution

I think I must integrate the electric field produced by small (differential) annulus from a to b. Wouldn't the electric field of one of them be [tex]\sigma A[/tex] where A is the area of such an annulus?

[tex]A=\pi ((a+dx)^2-a^2)\cdot \frac{\alpha}{\pi}[/tex] for the first annulus; [tex]\alpha[/tex] is the angulus shown in the figure.