My final notes on the PHYS143 optics lab, which is one that I am not really satisfied with.
Snells Law has usually not been covered in lecture before this lab comes up, which is fine. Optics has usually not come up either, and some faculty skip it entirely so that they can get to more “interesting” material.
For the PHYS143 students in particular, I think this could easily be expanded into a multi part lab that focuses more systematically on optics with an emphasis on gaining experience working with basic optical components. As it stands however, the lab just touches on Snells law and simple lenses in a fashion that feels like an afterthought, which it sorta is to be honest.
The concept for this part of the lab is the students are assumed to know the functional form of Snells Law. Assuming it has not been covered in lecture, this means the TA's have to provide a conceptual overview. By conceptual I emphasize I mean no derrivation from first principles, students will see that in lecture. Instead students need to know what the mathematical relationship is, the concept of index of refraction and that these things result in certain behavior when light rays encounter the boundary between materials with different indices of refraction.
Instead of viewing push pins through the refracting material, as is done in the 123/133 lab, students use the laser to create an incident beam which can be traced using the foam board pieces.
The purpose of the pins is to hold in place the refracting material, and the laser. Pencil markings on the paper are sufficient for defining the incident, reflected and refracted rays. Once all of the rays have been marked, the paper can be removed. A ruler can be used to draw in the rays based on the initial markings. Then the ruler and possibly a protractor can be used to measure the appropriate angles.
The goal of this part of the lab is twofold. Ultimately they are to use Snells Law to determine the index of refraction of a block of glass. They can use the pan of water, where water is assumed to have a known index of refraction, to develop and test their procedure for determining the index of refraction of the refracting material. This includes doing a careful assessment of uncertainties so that they can quantify how well they are able to determine the index of refraction for water. Then they apply their technique to the measurement of the glass block. The type of glass is not known, so this is a good example of making a measurement and drawing conclusions when the measured value is an unknown.