Lesson Waves and Wave Properties

Learning Objectives

After this lesson, students should be able to:

• Explain that waves transfer energy, not matter.
• Distinguish between mechanical and electromagnetic waves.
• Summarize the major properties and behavior of waves, including (but not limited to) wavelength, frequency, amplitude, speed, refraction, reflection and diffraction.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

Common Core State Standards - Math

International Technology and Engineering Educators Association - Technology

State Standards

Worksheets and Attachments

Introduction/Motivation

(In advance, make copies of the All About Waves—Notes Outline and Anatomy of a Wave Worksheet, one each per student, and have graph paper available for students. Also [optional], prepare to show students the attached 16-slide Waves and Wave Properties Presentation to accompany the lesson introduction. The slides are "animated" so you can click to show the next item when ready.)

Returning to our three-color mystery, today we are going to develop an understanding of the fundamental concepts of waves. What we learn will move us one step closer to reaching our goal of creating a solution to our engineering challenge that I explained yesterday (lesson 1 of this unit).

Let's start with what we already know. Why are we able to see? (Because there is light.) What is light? (It is a wave.) So, what is a wave? Well, we will learn the answer to that question today!

I will pass out an outline that will help you keep track of the important concepts explained as we talk about waves and wave properties.

(At this point, hand out the notes outlines and present the lecture material provided in the Background section, in tandem with the slides.)

(Next, so students can apply what they just learned, divide the class into groups of two students each, and hand out copies of the worksheets and blank graph paper.)

Who has ever sunburned your skin? Who has used a microwave to make popcorn? Or had an x-ray taken? Or listened to the radio? What do these activities have in common? (Listen to student answers.) All of these require waves.

One difference between the waves that pop popcorn and the waves that tan your skin is wave frequency. As we have learned, the frequency of a wave is defined as the number of cycles that pass a single point in a given amount of time.

In the first part of the worksheet, label the parts of a wave using the definitions given. Then, draw four different waves given information about the waves' properties. Of these four waves, your challenge is to identify the ones with the highest and lowest frequencies.

Lesson Background and Concepts for Teachers

Legacy Cycle Information: This lesson falls into the research and revise phase of the legacy cycle. During this phase, students begin to learn the basic concepts required to design solutions to the engineering challenge presented in lesson 1 of this unit. After lesson 2, students should be able to revise their initial thoughts, forming new ones that will help solve the engineering challenge question.

Waves and Wave Properties

(The following lecture material aligns with the slides.)

A wave is a disturbance that carries energy from one place to another. Matter is NOT carried with the wave! A wave can move through matter (called a "medium"), but some waves do not need a medium to be able to move. If a wave needs a medium, we call it a mechanical wave. If a wave can travel without a medium, (for example, through space), we call it an electromagnetic wave.

Wave Types

1. Transverse waves: Waves in which the medium moves at right angles to the direction of the wave. Think about a "stadium wave:" the people are moving up and down, but the wave is going around the stadium. Parts of transverse waves:

• Crest: the highest point of the wave
• Trough: the lowest point of the wave

2. Compressional (longitudinal) waves: Waves in which the medium moves back and forth in the same direction as the wave. Parts of compressional waves:

• Compression: where the particles are close together
• Rarefaction: where the particles are spread apart

Wave properties depend on what (type of energy) makes the wave. For example, you splashing in the ocean or an earthquakes creating a tsunami. Descriptive wave properties include:

1. Wavelength: The distance between one point on a wave and the exact same place on the next wave.
2. Frequency: How many waves go past a point in one second. The unit of measurement is hertz (Hz). The higher the frequency, the more energy in the wave.

• If 10 waves go past in 1 second, it is 10 Hz
• If 1,000 waves go past in 1 second, it is 1,000Hz
• If 1,000,000 waves go past, it is 1,000,000 Hz

3. Amplitude: How far the medium (crests and troughs, or compressions and rarefactions) moves from rest position (the place the medium is when not moving). The more energy a wave carries, the larger its amplitude.

• The energy of a wave can be expressed by the equation E = CA², where E is energy, C is a constant dependent upon the medium, and A is the amplitude.

4. Wave speed: Depends on the medium in which the wave is traveling. It varies in solids, liquids and gases. A mathematical way to calculate wave speed is: wave speed = wavelength (in m) x frequency (in Hz). Or, v = f x λ. So, if a wave has a wavelength of 2 m and a frequency of 500 Hz, what is its speed? (Answer: wave speed = 2 m x 500Hz = 1000 m/s)

Changing Wave Direction

1. Reflection: When waves bounce off a surface. If the surface is flat, the angle at which the wave hits the surface will be the same as the angle that the wave leaves the surface. In other words, the angle in equals the angle out. This is the law of reflection. (For example, when a pool ball strikes the side of a pool table, the angle at which it hits the bumper is the same angle at which it bounces off the bumper.)
2. Refraction: Waves can bend. This happens when a wave enters a new medium and its speed changes. The amount of bending depends on the medium it is entering. (optional: To explain this phenomenon in more detail, search the Internet to find an interactive tutorial that shows light being bent as it travels through a medium.)
3. Diffraction: The bending of waves around an object. The amount of bending depends on the size of the obstacle and the size of the waves. (optional: To explain this phenomenon in more detail, search the Internet to find an interactive tutorial that shows the diffraction of monochromatic light through slits of varying widths.)

• Large obstacle, small wavelength = low diffraction (bending)
• Small obstacle, large wavelength = large diffraction (bending)

Lesson Closure

Now that you're all experts in understanding the different types of waves, how they move and change direction, and how to describe their characteristics, tell me, what are some of the ways that you see waves used in your everyday lives? (Listen to student ideas.) Those are great examples. What about microwave ovens, medical and dental x-ray machines, eyeglasses and speakers? These are common examples in which engineers apply their knowledge of waves to design all types of useful products and tools that are evident in our everyday lives. To design these products, engineers must be well versed in all the properties of waves and how waves can differ from one another. For example, the waves emitted from a microwave are very different than those emitted from an x-ray machine that creates images of bones or teeth. Engineers need a complete understanding of wave properties in order to design safe and effective products!

But that's not all—engineers work to protect people and predict how tsunamis will travel after an earthquake in the ocean by using wave properties. To successfully predict where a tsunami will travel, engineers must understand how waves move and the properties associated with waves.

Another example of engineers using wave properties is when electrical engineers separate different types of waves so that the radio you are using tunes in to the right station, or your cell phone only picks up the calls that you want. If it were not for these engineers, you would constantly be getting calls from people you did not know. To accomplish this they must have a clear understanding of wave properties and know how to separate different types of waves.

Before designing and creating a solution to a challenge, engineers conduct research and gather information, just like you did today. This step is a crucial part of the engineering design process.

Vocabulary/Definitions

amplitude: How far the medium (crests and troughs, or compressions and rarefactions) moves from rest position (the place the medium is when not moving).

compression: When the particles of a longitudinal wave are close together.

compressional (longitudinal) wave: A wave in which the medium moves back and forth in the same direction as the wave.

crest: The highest point on a transverse wave.

diffraction: The bending of waves around an object.

electromagnetic wave: A wave that does not require a medium to travel, for example, it can travel through a vacuum. Also called an EM wave.

energy: The capacity to do work.

frequency: How many waves go past a point in one second. Measured in hertz (Hz).

mechanical wave: A wave that requires a medium to travel.

rarefaction : When the particles of a longitudinal wave are far apart.

reflection: When a wave bounces off a surface.

refraction: When a wave bends.

transverse wave: A wave in which the medium moves at right angles to the direction of the wave.

trough: The lowest point on a transverse wave.

wave: A disturbance that carries energy from one place to another.

wavelength: Distance between one point on a wave and the exact same place on the next wave.

Assessment

Note Taking: During the lecture, have students complete the All About Waves—Notes Outline and refer to it for visuals that supplement the lecture material. Then, with the notes turned over on their desks, ask students various questions that were covered in the lecture material. Evaluate students' answers to gauge their mastery of the subject.

Worksheet: After the lecture, have students complete the Anatomy of a Wave Worksheet to see how well they apply what they learned.

Trade-n-Test: To conclude, have each student make up their own wave properties (that is, trough and crest height and wavelength) and write it down. Then have students trade the "invented properties" papers with other students and draw the new waves based on the given properties.

References

Other Related Information

Browse the NGSS Engineering-aligned Physics Curriculum hub for additional Physics and Physical Science curriculum featuring Engineering.

Copyright

Contributors

Supporting Program

Acknowledgements

This lesson was developed through Clemson University's "Engineering Fibers and Films Experience – EFF-X" Research Experience for Teachers program, funded by National Science Foundation grant no. EEC-0602040. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.