Part 6b of the Polarization lab. The Faraday effect is when a material in a magnetic field changes the polarization of light passing through it. A glass rod is placed inside a solenoid so there is a magnetic field along its axis. A constant field rotates the polarization axis a tiny bit, but the effect is hard to see by eye. When a photodiode is used for the detector, we can use a few technical tricks to make the effect much more visible.