The problem statement, all variables and given/known data A metal disk is rotating with constant angular velocity in a constant magnetic field perpendicular to it. Use Faraday's law to fint the the induced voltage difference between the two points on the wire. The attempt at a solution So to use Faraday's Law, I need to first find an expression for the change in magnetic flux per unit of time inside a closed loop. However, from the drawing I can't find any loop where the magnetic field changes. The wire is connected to the disk with brushes, so I'm assuming that it doesn't rotate with the disk. Though, even if it did the magnetic field would still not penetrate it's interior.