Waves, Sound and Light Unit Plan
By Julie Montgomery
"Teaching High School Physics"
Physics 301
Fall 1999
Illinois State University
Carl J. Wenning, Instructor
I. UNIT OVERVIEW
A. Summary
This unit plan is intended to cover basic wave phenomena, sound and light. A conceptual approach will be emphasized, though formulas will be taught as well and students will be expected to solve problems. This unit ought to be appropriate for a Junior level Physics I class, and no math skills beyond algebra will be expected. The text book used will be Modern Physics by Frederick E. Trinklein.
B. Goals
At the end of this unit, I expect students to be able to define relevant terms in the areas of waves, light and sound. I expect students to be able to qualitatively describe wave behavior and phenomena of light and sound such as interference, the doppler effect, etc. I expect students to be able to demonstrate an understanding of basic formulae associated with waves, sound and light, and to be able to solve simple problems utilizing those formulae. I expect the students to design and carry out a simple experiment that will investigate one aspect of wave phenomena. At the end of this unit, I expect the students to have a better understanding of wave phenomena and how it affects the real world.
C. Rationale
1. Relevance to the student
An understanding of the wave nature of sound and light is fundamental to much of today’s technology. At the end of this unit, the students will have a better understanding of how television, radio, and many other things function.
As previously stated, much of the technology we use today is based on an understanding of waves, sound and/or light. The study of these topics is essential to society, since we must produce new engineers and scientists to maintain and advance our technology in these areas.
For the average student, the main relevance to the scientific profession as a whole lies in the formation of dispositions. We are educating people who will soon be adults, and even if they never use science in their future careers public sentiment impacts the sciences. It affects which programs get more funding than others or whether science programs even get funded at all. If we produce scientifically literate adults who have positive attitudes about science as a whole the scientific profession will be in much better financial shape.
At the end of this unit, the student will be able to:
At the end of this unit the student will demonstrate the ability to:
At the end of this unit the student will:
In The Handbook of Research on Science Teaching and Learning, Dorothy Gabel describes nothing in the way of alternative conceptions dealing with waves or sound, but briefly discusses light. According to Dr. Gabel, the large majority of students believe that light "brightens or illuminates" objects, thus enabling them to be seen, or that "the eyes play an active role in ‘reaching out and grabbing’ images."
In Physics begins with an M and Physics begins with another M, John W. Jewett discusses a great deal of alternative conceptions about waves, sound and light. Among them are:
Not applicable.
A. Slinky Demo
1. Wave Reflection/Transmission
2. Attach two springs with weak (but different) spring constants. Demonstrate that a pulse moving along one is partially reflected and partially transmitted when it reaches the boundary.
3. Zitzewitz, Paul W., Davids, Mark, and Neff, Robert F. 1992. Physics: Principles and Problems. MacMillan/McGraw-Hill Publishing Company.
B. Buzzer in a Bell Jar
1. Sound requires a medium to propagate
2. Place a buzzer in a bell jar hooked up to a vacuum. Suck all the air out while explaining to the students that without a medium to propagate in, sound cannot travel.
3. Personal Interview with Tom Holbrook, 1998
C. Speaker Demo
1. Interference
2. Place two speakers a distance apart and drive them at approximately 1000 Hz. Have the students move around the room and listen to the phase difference.
3. Personal Interview with Tom Holbrook, 1998
D. Xylophone
1. Harmonics, Consonance/Dissonance
2. Illustrate musical concepts of harmonics, consonance and dissonance by demonstrating on xylophone.
3. Personal Interview with Carl Wenning, 1998
E. Doppler ball
1. Doppler Effect
2. Place buzzer inside whiffle ball or nerf ball, attach string. Spin around overhead to demonstrate doppler effect
3. Personal Interview with Warren Montgomery, 1998
F. Forced vibration tuning fork demo
1. Forced Vibration
2. Place two tuning forks attached to resonance boxes next to each other, with the open ends of each box facing each other without touching. Strike one tuning fork, then place hand on it to stop its vibration. Other tuning fork will continue vibrating.
3. Personal Interview with Tom Holbrook, 1998
H. Tacoma narrows bridge
1. Resonance
2. Show video of Tacoma Narrows Bridge while explaining what’s happening.
3. Personal Interview with Tom Holbrook, 1998
I. Wave Interference
1. Wave Interference
2. Set up wave tank with three barriers so as to form two slits. Two spherical waves will be produced and interfere with each other.
3. Meiners, Harry F. (1970). Physics Demonstration Experiments. New York, NY: The Ronald Press Company.
J. Light Interference
1. Light Interference
2. Set up a laser to pass through a single slit slide and hit the wall. Observe interference pattern. Replace with double slit slide, and observe pattern.
3. http://storm.ph.utexas.edu/~phy-demo/demo-txt/6c10-10.html
In this experiment the student investigates the formation of waves in a string. He uses a buzzer to make the string vibrate, and alters the tension to cause standing waves to form.
Procedure: Clamp the buzzer about two thirds of a meter from an edge of the lab bench. Place the small stick at the edge of the table. Tie a 1 m long string to the buzzer, then tie a small loop in it at the other end and let the loop drop gently over the piece of wood. Turn the power supply on and then pull the string gently, slowly increasing the force. You should pull the string so that it goes from the buzzer over the piece of wood and then down to your hand. As you pull the string, watch for the formation of nodes and antinodes. They form and disappear as the force changes. Pull the string until you have two antinodes on it. In a string with fixed ends, the number of antinodes equals the harmonic… the second harmonic has two antinodes, the third has three, etc. With some buzzers it is possible to get just one antinode; most, however, will not buzz when the force is large enough to make just one antinode. If you pull too hard, you stop the buzzer or break the string. Reduce the force if the buzzer stops. After you have experimented with making the different numbers of nodes and antinodes, get values for the force which creates each standing wave. Do this by adding mass to the loop hanging down from the edge of the bench. The mass exerts a force equal to its gravitational force. Adding the mass takes a bit of patience because the standing waves have the tendency to come and go. Start by finding the mass required to cause the second harmonic. When you have found the mass, record it and the harmonic. Next, find the mass required to make the third harmonic. Record the mass and harmonic number. Then find the mass needed on the end of the string for as many other harmonics as possible. Some of the harmonics are multiples of other harmonics, like 6 which is twice 3. Multiples of harmonics are often hard to form. For some of your measurements, you can measure to smaller units of mass than you actually put on the loop. If the standing wave forms just after you start slowly placing a weight on the end of the string and then disappears when you have let go of the mass, then add the mass required to cause the standing wave is a fraction of the mass you added. Remove the masses and then use your hand to exert a force so that the second harmonic forms. Place your finger at the node in the middle of the string. Describe what happens. Finally, start with no force on the string and then slowly pull the string until the second harmonic forms. Describe what happens to the string and then slowly pull the string until the second harmonic forms. Describe what happens to the string as the force is increased.
Goodwin, Peter. (1990). Practical Physics Labs: A Resource Manual. Portland, ME. J. Weston Walch, Publisher.
B. Speed of Sound Lab
1. Speed of Sound
In this experiment, the students will be asked to determine what the best way of determining the speed of sound in air might be. Assistance and materials will be provided by the instructor as needed.
Procedure: Given nothing but a 5 meter long piece of string, a stop watch and two paper bags, use these materials to find the speed of sound. Formulate your own procedure for the collection of data. In your write-up list the steps that your group took. A major part of this lab is your procedure. Calculate the speed at which sound should travel in air at the temperature of the air. Find your relative error, and present your procedure to the class and report your value for the speed of sound. You will be going outside for this experiment. DO NOT leave the campus. DO NOT bother any other class. You must return the stop watch and string to the teacher and be back inside the room by 5 minutes before the class period is over. In your report answer the following questions: What factors that added to your error in this experiment were beyond your control? If you could have any equipment, how would you go about finding the speed of sound so as to give the most accurate answer?
http://explorer.scrtec.org/explorer/explorer-db/html/783751806-447DED81.html
C. A Sweet Lab on the Index of Refraction
1. Index of Refraction
In this experiment, using a clear plastic half-circle container, a protractor, a light source, sugar and water, the students will investigate how the index of refraction of water changes as sugar is added.
Procedure: Tape a protractor to the bottom of the plastic, half-circle container. The reference point for measuring the angles should be at the center of the flat side of the container. Make sure the protractor is positioned correctly. Ask your teacher to check how you attached your protractor. Fill the container about two-thirds full with water, set it on a few paper towels, and set up the light source so that it shines through the water and hits the flat side. Make sure that the beam of light is as thin as possible. Start with the beam of light striking the center of the flat side at zero degrees and increase the angle until you have total internal reflection. You can see if any light escapes by putting a piece of paper outside the container on the flat side of the container. Adjust the beam of light so that you have the smallest angle possible for total internal reflection. Precisely measure the angle which the light strikes the flat side and record it. Add the suggested amount of sugar to the water and stir it until it dissolves. Again find the smallest angle for total internal reflection. Repeat until sugar no longer will dissolve.
Goodwin, Peter. (1990). Practical Physics Labs: A Resource Manual. Portland, ME. J. Weston Walch, Publisher.
VIII. SAFETY CONSIDERATIONS
A. The Principal of a school is responsible for general building safety. He should ensure that adequate light and heat are provided, adequate workspace is provided, every science classroom has at least two unobstructed exits at remote ends of the room, Laboratory tabletops are made of a non-combustible material, master shut-offs are provided for gas, water, and electricity, electrical outlets are grounded, a fume hood is present, adequate storage space is provided for chemicals and supplies, fire extinguishers are present, a safety shower is present, face and eye showers are present, and regular inspections occur.
The Science Department Chairperson should, at least quarterly, discuss safety hazards in science instruction with all teachers and laboratory assistants, notify the principal in writing of any safety hazards, ensure that a first aid kit is present in each science room, inspect first aid kits and fire extinguishers, make certain that all combustible materials are safely locked up, inspect hardware and equipment, instruct the lab assistant or teacher to rehearse the procedures of each lab experiment prior to the class session, make sure that teachers do not allow materials that are safety or health hazards to accumulate, provide metal or earthware waste jars in each classroom, and ensure that teachers not qualified to teach science are not assigned to teach science classes.
Each science teacher must instruct the students in general safety procedures, and specific safety procedures relevant to the course. A set of safety rules ought to be posted in the room and made available to the students. The teacher must also remind the students of safety procedures at the beginning of each class session in which there may be an element of danger.
B. There are very few safety considerations in the subject areas of waves, sound and light. In dealing with sound I must ensure that all electrical equipment is safe and speakers do not emit painful or damaging levels of noise. When dealing with light, I must again ensure that all electrical equipment is handled safely and properly, and take special precautions with lasers.
C. In the bell jar demonstration, since a vacuum will be created inside the bell jar I ought to place a plastic shield in front of the demo to protect students in the event of an implosion. I also plan to use lasers, so I must be careful to ensure that the laser must be kept away from eye-level. No students should be allowed near the path of the laser beam, and no student should be allowed to use the laser without the instructor’s supervision. In the doppler ball demo I ought to be careful to ensure that the string is firmly attached to the ball and that the ball doesn’t strike anything… this is also why the ball ought to be a whiffle ball or nerf ball, to minimize any damage upon accidental impact. When working with speakers, I must ensure that the sound output doesn’t approach the pain threshold. If an injury occurs, I must immediately contact the office and request that a nurse be sent to help immediately. In the meantime, I must try to keep students calm and away from the area of the accident.
IX. SPECIAL STUDENT NEEDS
A. Student’s disability: Paraplegia
Paraplegia refers to a loss of use of two limbs. This is generally the two legs (spinal cord injuries will affect all areas downward from the point of injury, so if a spinal cord injury occurs above the arms quadraplegia will result, not paraplegia), but in the event of a stroke paralysis can result in one side of the body but not the other (such as left leg and left arm, or right leg and right arm). There are many different causes, but in any case the student is usually left wheelchair-bound.
B. Potential Handicaps
There are many potential handicaps, usually occuring in older buildings. Doorways may not be wide enough to accommodate wheelchairs, the boundaries that occur between doorways may be raised too high for a wheelchair to easily pass over, stairs may be present without an accompanying elevator. Within the classroom desks and tables may be at the wrong height to accommodate the student, and desk placement may prevent them from accessing many areas of the classroom.
C. Accommodations
First and foremost, I will talk to the student to determine what he or she considers to be necessary modifications. I would ensure that all necessary adjustments were made within my classroom, such as modifying desk arrangements or providing a table with easier access, and I would also inform the principal of accommodations that needed to be made within the building as a whole.
D. Enrichment Activity
A gifted student might be asked to design and perform his own experiment to investigate an area of interest related to the unit. I could generate a list of suggested topics if the student could not think of one on his own. I would also advise the student on the feasability of his choice, and provide suggestions and guidance throughout and the use of appropriate materials. The student would present a report explaining what he had found.
E. Students with Limited English Proficiency
If an ESL student was placed in my classroom, I would contact an ESL teacher either in the building if one was available for advice. I would certainly do my best to find resources that the student could understand, and have a translator provided if possible. I would also provide the student with a written set of notes each day so that he could review at his own speed.
X. STUDENT ASSESSMENT
A. I think a good assessment of student process skills would be the lab report they will turn in after performing the speed of sound lab. I’ve only provided the students with the materials to be used, and asked them to design and perform the experiment themselves based on their previously learned knowledge. This will therefore test the student’s ability to remember what was taught in class, apply it to a physical situation, construct hypotheses and perform an experiment without excessive direction.
B. It is difficult to assess dispositions, but one of my disposition goals is that I expect the student to demonstrate his competence as an intelligent consumer by selecting a light bulb according to its rating in lumens rather than only in watts. I would likely divide the students into groups of three and give them about a week in which to complete the assignment to account for students who may not have access to a vehicle or parents willing to take them to the store. I would require that at least one group member look at the various ratings of light bulbs available in a store, being careful to record all pertinent data. The group would then decide which light bulb would be the best to buy for an ordinary household lamp and write a summary of why they chose the way they did.
C. A portion of a test that evaluates students with three different learning styles might be:
Solve the following problem:
A train moving toward a station at 31 m/s blows its 305 Hz whistle. What frequency is detected by a listener standing at the station? What frequency is detected by listeners on a train moving away from the first train at a speed of 21 m/s?
Explain briefly why the doppler effect occurs. Does it occur only for some types of waves, or all types of waves?
Draw a diagram illustrating the doppler effect for sound waves where the source is moving away from the detector. Draw another diagram illustrating what occurs when the source moves faster than the speed of sound. Include labels.
XI. CONGRUENCE WITH STATE AND NATIONAL GOALS
Illinois State Learning goal number 11 states that students shall "Understand the processes of scientific inquiry and technological design to investigate questions, conduct experiments and solve problems." One of the labs I intend to perform in this unit addresses learning standard A assosciated with this goal by asking students to design and conduct their own experiment to verify the speed of sound. Illinois State Learning goal number 12 states that students shall "Understand the fundamental concepts, principles and interconnections of the life, physical and earth/space sciences." Many of the topics addressed in this unit are not only applicable to physics but also to chemistry, biology, and earth/space sciences. Learning standard C also requires a knowledge of wave theory specifically.
My speed of sound lab is intended to be taught with a guided inquiry approach. Other inquiry-based lessons may well be included at some point during the unit.
Benchmarks
In a physics classroom, the teacher has both the opportunity and responsibility to teach the students the basic principles of science. It is essential for students to be able to think critically and logically, form a hypothesis and test it, and generally follow the "scientific method." The basic principles of physics will also be essential for at least some of the students, as some will invariably go on to work in related fields. It’s possible for a student to never use anything they’ve learned after leaving their physics class, but it really is incredibly unlikely that they’ll be able to do so. Though they may never remember the equations they used, if they were given a basic understanding of the underlying phenomena, that understanding will probably last a very long time. This is what I hope they will retain. The fundamental understanding of what is going on in the physical world around them, the critical thinking skills that they’ve learned and the dispositions they hold will likely be far more germane to their lives than any equations or definitions could be. Critical thinking in particular is valuable to everyone, no matter what line of work they plan to follow.
The most important aspect of physics for the average student is probably mechanics. The laws of motion, basic definitions of velocity and acceleration, work and energy, linear momentum, the way objects behave in collisions, and gravity probably will be more valuable to the student than any of the other topics usually covered at the high school level, since they are the tools needed to describe the interaction of physical objects around them. A basic knowledge of electricity is also essential since we all deal with it on a daily basis, and sound and light may prove useful as well.
Keeping in mind that it is the underlying principles that will remain with the student and not memorizing definitions and formulas, I plan to teach from a largely conceptual approach. To that effect, inquiry-based learning opportunities will be utilized whenever I can afford the time and it is appropriate to do so. I also hope to maintain a cooperative atmosphere, although occasional competetive activities may prove useful as well.
XIII. REFERENCES
Zitzewitz, Paul, Davids, Mark, Neff, Robert, Wedding, Kelly. (1992). Physics: Principles and Problems. Peoria, IL: MacMillan/McGraw-Hill.