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## Homework Statement

Why is it that if you want to find an electric field over a ring, you take the derivative of the E equation (kq/r^2)? Like, here's an example.

"A 0.5 microcoloumb charge is distributed ona ring of radius 3cm. Find the electric field on the xis of the ring at 1cm, 2 cm, 3cm, etc."

Why is it that you have to take the derivative of the electric field equation instead of, like, the integral or something?