1. The problem statement, all variables and given/known data J=J(r)(θhat), J(r)=(3ITr2)/R3 a)total current of the disk? b)J(r) was brought by a charge disk spinning at ang vel. ω, find the surface charge dens σ(r)? 2. Relevant equations J=I/πr2 I=∫Jda J=vσ 3. The attempt at a solution a)I assumed I would have to integrate J(r)da from 0 to R to get the total current I=from 0 to R∫Jda=from 0 to R∫(3ITr2)/R32πrdr I=(3πITR)/2 But the result doesn't make sense? How can I prove? b) σ= (3ITr2(θhat))/R3ωrθ am I using the right expression "θ" for the rotating angle or should I use ∅?