This lab has become more of an introduction to polarization. Many faculty now use the last few weeks of the quarter to go into stat mech, so they don't get to polarization at all. So currently it puts the TA's in a bit of a bind to have to qualitatively explain the following:

• Polarization and linear polarizers.
• Projection onto pass axis.

The first part of the lab uses the Vernier Optical Rail with their light sensor connected to a labquest mini. I give the students 4 “cases” to consider. For each case they have to come up with a prediction for the result of the measurement, then experimentally verify their prediction quantitatively. Some key points I emphasize to the TA's:

• Optical components are never “ideal”. So even in the crossed configuration there will be some light that makes it through them. This is an Experimental Bias, students should notice it and figure out a way to account for it. “Accounting for it” is not expected to be rigorous. It can be something as simple as observing and noting that any light source they look at with crossed polarizers they see some light.
• There will be ambient light reaching the detector. Students should notice this and figure out a way of quantitatively accounting for it.
• Uncertainties in measured values should be recorded and taken into account when they assess the correctness of their initial expectation.
• The third case is analogous to the quantum eraser phenomena. Students will not have seen polarization in class yet, but this can be understood in terms of plane waves superimposing and the resultant wave being projected onto the pass axis of the polarizer. Be prepared to walk students through this, but wait till they get to this part of the lab when it will have more impact.

The second part of the lab (going in order of appearance in the Wiki) is purely show and tell. They do not have to do or say anything about it in their out of lab assignment. The yellow squishy material illustrates how cross polarizers can be used to detect stress lines in a material. The piece of quartz is used to illustrate the effect of birefringence. I simply want students to see these things, how much they get out of the exercise pretty much depends on how you interact with them during the lab.

The third part of the lab is Brewsters Angle. This one is a bit tougher to provide a qualitative description of for students who do not see it in lecture. In the wiki they are given a the relationship for Brewsters angle and the index of refraction for glass so that they can calculate the angle. Then they are supposed to use the spectrometer and polarizer to verify through observation that the refracted and reflected ray polarizations show the expected behavior. Note that I do not use the cameras on the eyepieces. I feel that the mounting mechanism is too problematic and not worth the gains. Assessment of the effect is qualitative.