This lab is run similar to the PHYS 123/133 version. Main differences are noted below.
For this part I finally admitted defeat and dropped the pulsed time of flight method. It has a lot of potential but the speakers produce too much ringing and distortion from the square wave.
Students only do the interference nodes method. I do have them compare their speed of sound to what they measured the previous week in the sound waves lab. I point out to TA's that things like temperature and air pressure impact the speed of sound in air so the point is not to show “agreement” between the two measurements.
I do the qualitative exercise with listening for beats at two different frequencies with the speakers held together by one ear, and again with a speaker in each ear.
The scope part I do different from the 120's and 130's. For this part my emphasis is on demonstrating how the phenomena of beats can be used to make extremely precise measurements of the frequency difference between two sine waves. Here I am thinking of PNMR where the apparatus mixes the RF signal with the FID signal to generate beats for determining when you are on resonance.
Essentially I have them set the two function generators to the same frequency as well as can be determined by the display on the function generators. Then they look at both outputs on the scope at the same time. They are asked to use the cursor feature of the scope to measure the frequency of each sine wave as accurately as possible this way. Then they switch to math mode, sum or subtract the two signals and observe the beats on the scope. Then they measure the frequency of the beat cycle which clearly gives a much more precise measurement than trying to measure the frequencies of each sine wave separately. For this part I expect full and proper assessment and propagation of uncertainties to reinforce the point.
I demonstrate to the TA's how to setup the scope to use math mode, but I do not put any instructions in the wiki for students. I want them to make as much progress as they can just pushing buttons on the scope and trying things before the TA shows them how to do it.
This part is pretty similar to the 120's and 130's. They just build an interferometer and measure the wavelength of the microwaves. I emphasize to the TA's that the students probably have not seen a michaelson interferometer in lecture, so they need to be prepared to walk the students through a conceptual understanding of what is going on.