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## Homework Statement

A thin flat washer lies in the x − y plane, with the center at the coordinate origin. The washer has an inner radius R1 and an outer radius R2 (so it looks like a disk of radius R2 with a concentric circular cut-out of radius R1). The surface of the washer is uniformly charged with a surface charge density σ.

1. (a) What is the electric field (as a vector) at the distance z along the z-axis (which coincides with the axis of symmetry of the washer)?[Hint: subdivide the washer into infinitely thin concentric rings.]

## Homework Equations

E=q/r^2 (electric field due to a point charge)

## The Attempt at a Solution

I know that you have to integrate in order to determine the total magnitude of the entire washer on the point, but I'm not sure if I'm going about setting up the integration the right way. Currently, I have dE= k(δds)/(R2^2-R1^2), where δ represents the surface charge density of the washer. Any hints as to where to go from here would be appreciated.