Properties of Waves

Lab Assignment 11: Properties of Waves

Instructor’s Overview

If you think carefully about it, we are immersed in waves. The fact that you can
turn on a radio and listen to music or news, or receive a cell phone call is
evidence of the transmission and reception of waves. These two examples
involve transverse electromagnetic waves. Having a conversation with a family
member, friend, or colleague is made possible by longitudinal waves of sound.
Waves transmit energy and demonstrate interesting properties such as
superposition (constructive/destructive interference) and resonance. We’ll
explore 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 in
detail in the eScience manual. Here is a quick overview:

• eScience Lab 21 Experiment 1: In the first part of the lab, you will use a

  Slinky® to create and visualize transverse and longitudinal waves. You’ll
  experiment with wave reflection, superposition, and resonance.

• eScience Lab 21 Experiment 2: In the second part of the lab, you will
  create your own wave source using a cork and a tub of water. This
  experimental setup allows you to explore the Doppler effect.
• eScience Lab 24 Experiment 2: In the final part of the lab you will
  explore the concepts of pitch and resonance by experimenting with water-
  filled bottles.
  Take detailed notes as you perform the experiment and fill out the sections
  below. This document serves as your lab report. Please include detailed
  descriptions of your experimental methods and observations.
  Experiment Tips:

• In general, read the lab questions below before running the experiments. This
  allows 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 floors
  dampen the wave behavior and make the experiments more ambiguous.
• For the Doppler effect experiment, it is easier to see the wave behavior with a
  larger tub of water. Wave reflection from the sides of small tubs make the
  observations more challenging.
• Narrow neck glass bottles work well for the sound experiments in eScience
  Lab 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 following
questions:

1. Whathappenedwhenthetransversewavesreachedyourpartner’send?Did
   the reflected wave stay on the same side as the one you sent? Draw a
   diagram showing the incoming and reflected waves.
2. Didthewavesgoanyfasterorslowerwhenyoutriedavarietyofamplitudes?
   Explain how this agrees or disagrees with the equation for a transverse
   wave’s velocity.
3. Whatdidyounoticeaboutthespeedofthelongitudinalwavescomparedto
   the transverse waves?
4. Explainwhathappenedwhenyouandyourpartnerbothsentwavesonthe
   same 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,explainhowmusicalinstrumentscreatehigherand
lower 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 the
following questions:

1. Drawapictureofamovingsourceandthewavessurroundingitaccordingto
   what you observed in this experiment. How does the spacing of the
   wavefronts in front of the source compare to those behind it?
2. Imagineasmallobserverispositionedinfrontofcorkinyourpictureabove.
   As the cork approaches, the observer measures the wavelength of the waves
   passing by. How does this wavelength compare to that measured from behind
   the source?
3. Imaginethatthissameobservermeasuresthefrequencyofthewaves
   instead of wavelength. How does the frequency measured in front of the
   source appear to the observer compared to the frequency measured from
   behind?
4. Howdotheseresultshelpexplainwhyacar’senginesoundsdifferentasthe
   car approaches you compared with after it passes?
5. TheDopplereffectispresentinlightwavesaswell.Asyouwilllearnin
   Physics II, red light has a lower frequency than blue light. Based on your
   observations in this experiment, what can you speculate about the motion of a
   distant star that appears “red‐shifted” to astrophysicists? (The light appears
   more red than expected.)

eScience Lab 24 Experiment 2: Pitch and Resonance

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

1. Didthepitchofthenoisemadebystrikingthebottlegethigherorloweras
   you filled the bottle with water?
2. Didthepitchmadebyblowingacrossthetopofthebottlegoupordownas
   you filled the bottle?

1. Whyisthereadifferencebetweenthesetwonoises?Inyouranswer,
   comment on the source of the noise in each case (i.e. What is vibrating?).
2. Usingwhatyouknowaboutharmonicsandresonance,explainhowdifferent
   pitches are created when you blow across the bottle opening with different
   liquid levels.
3. Whatwavepropertyallowedyoutohearnoisethroughyourbottleinstep2of
   Procedure 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