Lab Assignment 11: Properties of Waves

Instructor’s Overview

If you think carefully about it, we are immersed in waves. The fact that you canturn on a radio and listen to music or news, or receive a cell phone call isevidence of the transmission and reception of waves. These two examplesinvolve transverse electromagnetic waves. Having a conversation with a familymember, friend, or colleague is made possible by longitudinal waves of sound.Waves transmit energy and demonstrate interesting properties such assuperposition (constructive/destructive interference) and resonance. We’llexplore many of the properties of waves in this final lab of Physics I.

This activity is based on Labs 21 and 24 of the eScience Lab kit.

Our lab consists of three main components. These components are described indetail in the eScience manual. Here is a quick overview:

• eScience Lab 21 Experiment 1: In the first part of the lab, you will use aSlinky® to create and visualize transverse and longitudinal waves. You’llexperiment with wave reflection, superposition, and resonance.
• eScience Lab 21 Experiment 2: In the second part of the lab, you willcreate your own wave source using a cork and a tub of water. Thisexperimental setup allows you to explore the Doppler effect.
• eScience Lab 24 Experiment 2: In the final part of the lab you willexplore the concepts of pitch and resonance by experimenting with water-filled bottles.Take detailed notes as you perform the experiment and fill out the sectionsbelow. This document serves as your lab report. Please include detaileddescriptions of your experimental methods and observations.Experiment Tips:

• In general, read the lab questions below before running the experiments. Thisallows you to keep an eye out for specific things as you run the experiments.
• Make sure to run the Slinky® experiments on a hard floor. Carpeted floorsdampen the wave behavior and make the experiments more ambiguous.
• For the Doppler effect experiment, it is easier to see the wave behavior with alarger tub of water. Wave reflection from the sides of small tubs make theobservations more challenging.
• Narrow neck glass bottles work well for the sound experiments in eScienceLab 24.

Date:Student:

Abstract
Introduction
Material and Methods

Results

eScience Lab 21 Experiment 1: Slinky®

Based on your results from the Slinky® experiments, please answer the followingquestions:

1. Whathappenedwhenthetransversewavesreachedyourpartner’send?Didthe reflected wave stay on the same side as the one you sent? Draw adiagram showing the incoming and reflected waves.
2. Didthewavesgoanyfasterorslowerwhenyoutriedavarietyofamplitudes?Explain how this agrees or disagrees with the equation for a transversewave’s velocity.
3. Whatdidyounoticeaboutthespeedofthelongitudinalwavescomparedtothe transverse waves?
4. Explainwhathappenedwhenyouandyourpartnerbothsentwavesonthesame side. What kind of interference took place?
5. Whathappenedwhenwavesonoppositesidespassedeachother?
6. Howdidshorteningthelengthofthespringaffecttheresonantfrequencies?How does this confirm the relationship v = λ f when velocity is constant? (Hint:

a shorter spring length means smaller wavelengths for each standing wave).

7. Usingthisknowledge,explainhowmusicalinstrumentscreatehigherandlower tones. Use a string instrument as an example.

eScience Lab 21 Experiment 2: Doppler Effect

Based on your results from the cork and water experiment, please answer thefollowing questions:

1. Drawapictureofamovingsourceandthewavessurroundingitaccordingtowhat you observed in this experiment. How does the spacing of thewavefronts in front of the source compare to those behind it?
2. Imagineasmallobserverispositionedinfrontofcorkinyourpictureabove.As the cork approaches, the observer measures the wavelength of the wavespassing by. How does this wavelength compare to that measured from behindthe source?
3. Imaginethatthissameobservermeasuresthefrequencyofthewavesinstead of wavelength. How does the frequency measured in front of thesource appear to the observer compared to the frequency measured frombehind?
4. Howdotheseresultshelpexplainwhyacar’senginesoundsdifferentasthecar approaches you compared with after it passes?
5. TheDopplereffectispresentinlightwavesaswell.AsyouwilllearninPhysics II, red light has a lower frequency than blue light. Based on yourobservations in this experiment, what can you speculate about the motion of adistant star that appears “red‐shifted” to astrophysicists? (The light appearsmore red than expected.)

eScience Lab 24 Experiment 2: Pitch and Resonance

Based on your results from water bottle experiments, please answer the followingquestions:

1. Didthepitchofthenoisemadebystrikingthebottlegethigherorlowerasyou filled the bottle with water?
2. Didthepitchmadebyblowingacrossthetopofthebottlegoupordownasyou filled the bottle?

1. Whyisthereadifferencebetweenthesetwonoises?Inyouranswer,comment on the source of the noise in each case (i.e. What is vibrating?).
2. Usingwhatyouknowaboutharmonicsandresonance,explainhowdifferentpitches are created when you blow across the bottle opening with differentliquid levels.
3. Whatwavepropertyallowedyoutohearnoisethroughyourbottleinstep2ofProcedure 2, and how does the sound transmit from one bottle to the other?Did the pitch sound the same as the one made by your partner?

Conclusions

References