1. The problem statement, all variables and given/known data A very thin disk of non-conducting material initially holds a charge QO = +5 μC that decreases with time t as Q(t) = QO e-t/τ where τ = 10 seconds. If the disk has a radius of 0.10 m, what is the magnitude and direction of the magnetic field at the circumference of the disk as a function of time? 2. Relevant equations Assume at any time t that the displacement vector D is uniform across the disk. There is no free current. ∇[itex]\bullet[/itex]E = (1/εO)ρ ∇×B = μOJ + μOεO (∂E/∂t) 3. The attempt at a solution I tried to just work out the curl of B and I immediately ran into problems and it's not correlating to the problem.