A very thin plastic ring $($radius R$)$ has a constant linear charge density, and total charge Q$.$ The ring spins at angular velocity about its center, which is the origin. What is the current I, in terms of given quantities? What is the volume current density J in cylindrical coordinates? $($This may be a little tricky, since the ring is $$very thin,$$ there will be some functions. Hint: write down a formula for $($s$,,$ z$)$ first. And, remember that J should be a vector!$)$