Standing Waves Lab

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Stony Brook University *

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133

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Mechanical Engineering

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Feb 20, 2024

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docx

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5

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PHY 133 L07 Standing Waves Jeremiah Shawn Geotina Lab partner: Christopher Kim TA Loc, Ngo Experiment Date: 19 April 2023 Report Date: 26 April 2023
Introduction In this experiment we are going to observe and analyze the properties of standing waves on both stretchy and rigid strings. To do this we are going to use an electric motor, a variable power supply, a photogate, 1 stretchy and 1 rigid string, a pulley, various masses, 1 meter stick, and a scale. We generate certain expectations that we have of the strings and experimentally generate values, allowing us to confirm the properties of these phenomena. Procedure: Part I: Predicting Stretchy-String Wave Velocity 1. Weigh the full length of the yellow and gold stretchy string on a scale to determine its mass, m. 2. Push the string through the hole in the metal bit that is hanging from the motor as well as the post, and hold it steady with a binder clip. 3. Put the loop of the stretchy string over your pulley. Hang 150g of mass from the end of the loop, making sure it's neither at the pulley nor on the ground. Record this mass as M, with an uncertainty of 0.1g. 5. Measure and record the lengths L and δL, with appropriate uncertainties. Part II: Measuring Stretchy-String Wave Velocity 1. Set up your photogate with the file "Standing Waves" and place it above your motor where the little "flag" is. 2. Look at your power supply. If there is only one knob, that's the knob you'll be turning to adjust the frequency of your motor. If there are three, set the "current" knob to maximum, and adjust the other two to set the frequency. 3. Turn on your motor and adjust the frequency until you see a steady pattern of some definite number of half-waves. Count the number, which is n. 4. Vary the frequency and observe what values of n you can reach with the power supply. You want at least four different possible n, and ideally at least seven. 5. Set your frequency to approximately the least n you can get and adjust it until you maximize the amplitude. Record n and start recording with your photogate. 6. Record a typical value for the period, T. Neglect uncertainty. 7. Repeat this measurement for a variety of n as many as you can get. Part III: Measuring μ of the Fixed-Length String
1. Weigh the fixed-length (orange or white, non-stretchy) string, hook it up to your motor, and tie a loop if needed. 2. Hook it over the pulley, attach a 100g mass to make it taut, and measure L and δL again. 3. Choose a value of n to work with for this experiment. Record this n. 4. Replace the 100g mass with a 50g mass and record this as M. Measure the period with the photogate. Repeat, adding 50g each time up until a total M of 250g. Neglect uncertainties in M in this part. Results, Analysis and Discussion (include .xlxs file) Analysis + Discussion: .xlsx file: https://docs.google.com/spreadsheets/d/1sdjqJZ70aFxIAr2ZeZGF_hrpcn6ITLLA10mXIYIZs44/edit?usp=sharing
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