Unit / Waves
Enduring Understanding / All waves, regardless of origin or type, transmit energy from one place to another and share a common set of characteristics that explain their behavior. Wave behavior can be used to understand and explain many everyday phenomena.
SOL Objectives / PH.8 The student will investigate and understand wave phenomena.
Key concepts include
a) wave characteristics;
b) fundamental wave processes; and
c) light and sound in terms of wave models.
Title / Changing Mediums in Waves
Lesson Objective / To discover the wave equation (v=fλ) and many properties of waves when striking an interface and changing materials
Inquiry Level / 3
Materials Required / Super slinky, long tight coiled (brass) spring, stopwatch, meterstick or tape measure. Some students use cameras for video analysis.
Waves through Mediums… Introductory brainstorming.
With your assigned group:
List three different types of waves you have experience with in your life / 1) / 2) / 3)List a few properties we can measure about each wave.
what medium do they generally travel through?
What is one way to change/modify the medium?
Predict what will happen to the wave properties you listed when the wave passes from the first medium to the second.
Waves Through Mediums LAB
For this lab, we’ll be examining a slinky wave as it passes from one type of spring to another. Your objective is to discover and uncover some of the things that happen when a wave strikes a boundary between two materials.
- You don’t have to use the full length of each spring all the time
- Remember you can send waves from AB or from BA
- You can send single crisp wave pulses, or continuous sinusoidal wave trains.
- Some outcomes are qualitative, some are quantitative.
- Some outcomes are unexpected. Keep alert.
Based on what we’ve seen and measured in our slinky labs so far, list at least three different wave properties that you can observe when a wave strikes a boundary between two materials, and predict what you think will happen for each.
2)
3)
Once your teacher has approved your list of things to observe, get a set of springs and head into the hallway ready to observe.
Test your predictions with a variety of different scenarios. While testing, you’ll be able to qualitatively assess your predictions and you should be able to see some additional wave phenomena at the same time. Record your observations for the three wave parameters you chose, and record three additional observations about waves and changing mediums from your experimentation.
1)2)
3)
+1)
+2)
+3)
Once you have made your observations, return to the classroom and carefully return the springs to their safe place.
Write at least one clear outcome of your experiment on the board to share and discuss.
Record here additional and important wave phenomena uncovered by peers that we discuss in class
++1)++2)
++3)
Waves through Mediums, Part 2: Quantitative measurements.
Are waves predictable? Modern society requires the manipulation of many types of waves. Sound, light, and radio are probably the most common waves we “harness” for communication. But what happens when a wave changes mediums? Can we predict what will happen?
In the first portion of this lab, you observed a great deal of interesting things that happened at the boundary between two waves and how the parameters of a wave changed as it passed from one material to the next.
Starting with these observations, we want to expand our understanding to be able to make some measurements and,by understanding the materials, be able to make predictions.
Our ultimate goal is to determine how to predict the wavelength of a wave in the second medium.
You and your partner must come up with things to test, parameters to change, things to keep constant, and measurements to make.
In the end, if your teacher gives you a certain wavelength in one material, you should be able to predict the precise wavelength in a second, known material.
Before heading to the hallway, brainstorm at least one plan to conduct an experiment that will allow you to measure wave properties, change a parameter (while keeping others constant) and observe and measure new outcomes. Uncovering the relationships between the wave properties might take several tries. This is just your first. Write down your plan, and draw up the data table you will use.
Data Table:
Get this method approved by your teacher, then head out in the hallway and give it a try.
Record your data in the table you created, be sure to use proper units.
Odds are, you’ve got some additional brainstorming to do, some additional testing to do, and maybe whole new sets of data. On additional sheets of paper, create a clear and organized procedure and an organized table of data. Remember you don’t have to use both springs all the time, nor the full length of both all the time. You decide what you can modify and test. Your grade will be based on clearly communicating a procedure, experimentation, data and analysis.
TEACHER NOTES:
The twofold purpose of this lab is to have additional hands-on exploration of waves, specifically boundary phenomena, and most importantly for students to discover the wave equation (v=fλ).
This inquiry lab is to explore phenomena when waves pass from one material to another. A long slinky attached to a long tightly coiled (brass) spring works to nicely show these phenomena. It is expected that students have already explored the basic wave phenomena and relationships, but have NOT been dictated the wave equation ( v=fλ ). Through this lab, this relationship reveals itself as a way in which speed and wavelength are inversely related, and where frequency is a constant. This is the goal of this inquiry, so don’t give it away! Student understanding of f=v/λ is a clear outcome of this lab.
Students may not come up with all observables easily, but should be allowed to flounder and discover.
Some things they should pay attention to:
Speed of wave, amplitude of pulse, frequency, phase (is the pulse on the left or right side of equilibrium, and does it change when striking the interface), reflections (does phase change?) , effects of changing tension, and more.
A motivating example that could help them start to think, but wouldn’t reveal too much, might be examining a laser beam as it enters a glass of water (air to glass to water to glass to air). Students can’t see everything happening, but can start thinking about possibilities.
Another example would be radiowaves passing through walls, or even different layers of our atmosphere. Why might we find these phenomena important to explore and understand?
To help guide student thinking, at some point help them differentiate between the things they can determine, select, or modify, and what things are determined because of other parameters. For example, they can choose frequency by their hand-shaking-rate. Can they choose wavelength? How?
Teacher will check for the key ideas:
At boundary:
- Partial reflection
- Phase shift
- % transmission vs. reflection
- tight to loose vs. loose to tight. effect is different. (AB vs. BA)
Transmitted wave:
- Change in amplitude
- Change in wavelength
- Change in wave speed
- NO change in frequency
AFTER qualitative portion, we return to the seats and look at what we can determine QUANTITATIVELY. This should lead to the guiding question:
How can we predict the wavelength of the transmitted wave?
Ask students for ideas about predicting amplitude of the wave.
Have students brainstorm, then share their ideas.
There could be multiple correct answers for this, so students can generate ideas, vote, share, etc.
Why do you lose amplitude as the wave travels? What does this say about the meaning of the amplitude (it is a pack of energy!)
Follow-up discussion with class:
Their work, with prompting for some groups, should lead them to the relationship we call the wave equation.
What are the implications of this outcome? Why is it important, what does this help us learn about waves, etc. How do our new understandings help us figure out wave phenomena? What does it matter? What IS the wave equation?
Groups that have a hard time getting numbers could possibly transition to the “wiggler” lab (vibrating string showing harmonics in resonance), but that lab activity is very cookbook and understanding resonance patterns may be more difficult for some groups at this point.
Questions or suggestions? Contact Aaron Schuetz at Yorktown