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## Homework Statement

I have a ring, radius a, with a charge distributed evenly around it. Using a gaussian cylinder of radius r, r<<a (or otherwise). Find the electric field at at small distance r away from the centre of the ring, r is in the plane of the ring.

I know that the answer is

[tex]\frac{Qr}{8\pi\epsilon_0 a^3}[/tex]

## Homework Equations

[tex]\int E\cdot ds = Q/\epsilon_0[/tex]

## The Attempt at a Solution

I can't get started since I find that the charge enclosed is 0

Thanks