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## Homework Statement

There is a disc with radius R which has a uniformly-distributed total charge Q, rotating with a constant angular velocity w.

(a) in a coordinate system arranged so that the disc lies in the xy plane with its center at the origin, and so that the angular momentum point in the positive z direction, the local current density can be written J(x,y,z) = K(x,y) d(z). determine the surface current K(x,y) in terms of Q, w, and R.

(b) using the Biot Savart law, determine the magnetic field at point r=sk, k is the vector direction. find the same for r=-sk.

## Homework Equations

Biot Savart Law

## The Attempt at a Solution

I obtained K= Q(w X R) / pi*R squared for part A, but I'm not sure how that's supposed to fit into the Biot Savart Law.