====== Interference (PHYS143) ====== ====== Theory ====== ---- This experiment makes use of the concepts of superposition and interference of waves. You have seen this material in lecture, if you need a refresher we provide a brief summary [[phylabs:lab_courses:phys-140-wiki-home:spring-experiments:interference-lab:interference_theory|here]]. ====== Experimental procedure ====== ---- ===== Lab notebook template ====== One member of the group should click on the link below to start your group lab notebook. (You may be asked to log into your UChicago Google account if you are not already logged in.) Make sure to share the document with everyone in the group (click the "Share" button in the top right corner of the screen) so each member has access to the notebook after you leave lab. Choose one member of your group to be the designated **record-keeper**.
[[https://docs.google.com/document/d/1eJobZ-5b57w_Y7_jg0S9ArY3K3Wfs-mgajQ5_tlqdMg/copy|Lab Notebook Template]]
The record-keeper role will rotate each week so that everyone gets a chance at it. If a group has three students and does six weeks of lab, then each group member is expected to be record-keeper twice during the quarter. ====== Superposition and Interference ====== {{ phylabs:lab_courses:phys-120_130-wiki-home:spring-experiments:pxl_20220418_200220771.jpg?400 |}} ===== Interference of sound waves ===== For this part of the lab your apparatus consists of a pair of speakers, a function generator, and a sound pressure level (spl) meter. You will use this apparatus to generate pairs of sine waves with different cases consisting of different combinations of frequency and phase. For each case you are asked to predict what the resultant waveform will look like for the superposition of the sound waves from the two speakers. You will then setup the apparatus to create the appropriate waves and measure the resulting wave to (hopefully) confirm your prediction. You should also try to "hear" the effect of the interference of the two waves. The different cases are: - Two sine waves of the same frequency and amplitude, in phase with one another. - Two sine waves of the same frequency and amplitude, with a phase difference of $\pi$. - Two sine waves of the same amplitude with a frequency difference of 1hz. - Two sine waves of the same amplitude with a frequency difference of 10hz. ===== Tuning Fork ===== The phenomena of beats is at the root of how musical instruments such as pianos, guitars, violins etc are tuned. If you happen to play a musical instrument you may already be familiar with using a strobe tuner to tune an instrument, or tuning by ear to a reference tone. In either case you are making use of the beat frequency between the string you are tuning and the frequency to which you are tuning. When tuning by ear you listen for the beat frequency and adjust the tension in the string of your instrument until the beat frequency goes to zero. In this part of the lab we want you to determine the frequency of your tuning fork (note that the frequency of the fork is marked on the base of the fork, which we have covered with tape) both by ear (if possible, and more precisely by looking at the beat frequency on the scope. ===== Microwave interference using a Michelson interferometer ===== {{ phylabs:lab_courses:phys-120_130-wiki-home:spring-experiments:pxl_20220418_200207101.jpg?400 |}} For the second part of the lab you will measure the frequency of microwaves produced by a PASCO microwave transmitter by measuring the speed of light and then the wavelength of the radiation from the transmitter. The measurement of the speed of light will be accomplished by using the apparatus already setup for you along the top shelf against the west wall of the lab. One end of the room there is a low power red light laser which produces short pulses of light. These pulses of light travel the length of the bench where they hit a mirror and are reflected back to where they started. A 50/50 beam splitter is used to send some of the out going and some of the reflected pulses into a photodetector. The signals from the photodetector can then be displayed on a scope where the time between the emitted and reflected pulses can be measured accurately. A ruler and tape measure are provided to measure the round trip distance. To measure the wavelength of the microwaves you will build a Michelson interferometer. If you are unfamiliar with how a Michelson interferometer works, [[http://https://en.wikipedia.org/wiki/Michelson_interferometer|wikipedia has a nice description.]] To construct your interferometer you have both a microwave transmitter and a receiver, two metal reflectors, and a white board which is made of a material that is 50% reflective for microwaves. Arrange these components to build your interferometer. Then by changing the path length of one of the arms of the interferometer while monitoring the intensity of the output, you can find the wavelength. ===== Submit your lab notebook ===== Make sure to submit your lab notebook by the end of the period. Download a copy of your notebook in PDF format and upload it to the appropriate spot on Canvas. **Only one member of the group needs to submit to Canvas, but make sure everyone's name is on the document!** When you're finished, don't forget to **log out** of both Google and Canvas, and to close all browser windows before leaving! ====== Report: Summary and conclusions ====== ---- After the lab, you will need to write up your conclusions. This should be a separate document, and it should be done //individually// (though you may talk your group members or ask questions). Include any data tables, plots, etc. from the your lab notebook as necessary in order to show how your data support your conclusions. The conclusion is your interpretation and discussion of your data. What do your data tell you? How do your data match the model (or models) you were comparing against, or to your expectations in general? (Sometimes this means using the $t^{\prime}$ test, but other times it means making qualitative comparisons.) Your conclusions should always be based on the results of your work in the lab. It is **not** acceptable to evaluate the results of an experiment by comparison to known values or any other form of preconceived expectation. Your conclusions need to be supported by your data. If your data are inconclusive or in disagreement with regard to your expectations then your conclusion should reflect that. **REMINDER**: Your report is due 48 hours after the lab. Submit a single PDF on Canvas.