Waves Teacher Guide






Grade Level


Activity Names

Interference with Light

Ripple Tank

Taking Waves Apart

The Shape of Sound Waves

Being Prepared

Intensity of Light & Ripple Tank - Individual students working with accountability/discussion partners would be the ideal situation (after an intro that models getting the simulation properly set up).

Taking Waves Apart & The Shape of Sound Waves - Students are going to be analyzing noises they are making that are picked up by a microphone (can be the one built in to the computer), so a quiet room or an optional room is a must or have only about half of the students actually making the noises at a given time.

Getting Started

Intensity of Light & Ripple Tank - This simulation is really rich, so it is especially important to model what to select/click on in addition to emphasizing to the students the importance of reading all directions and questions carefully. If students are on the incorrect tab they will be really confused when they try to answer the question.

Taking Waves Apart - two simulations, but one requires your computer to have a microphone (so a quieter area or fewer students participating simultaneously)

The Shape of Sound Waves - the simulation requires a microphone (so a quieter area or fewer students participating simultaneously)

Suggested Timeline

Interference of Light and Ripple Tank would be about 1 (48 minute) class period each, as long as you model the setup of the model well. Some discussion should happen between, as well as some introduction before. I would show a video clip of the Tacoma Narrows Bridge and have the students discuss the motion of the bridge and have them think about how this is similar/different to light waves.

Before Taking Waves Apart, I would have the students make both longitudinal and transverse waves using slinkies or snakeys (see science supply catalogs) and discuss with them the difference between the two types of waves, and which waves are which type.

Taking Waves Apart would likely take 1 1/2 to 2 (48 minute) class periods due to the cooperation and quiet necessary to analyze the sound and the challenge of matching the shape of the graph at the end.

The Shape of Sound Waves would likely take around 2 (48 minute) class periods for a freshman/sophomore physical science class due to the high level of unfamiliar terminology. If the class was a physics class, it might be possible to do it in less time.

Thinking about the Discovery Questions

This unit is motivated by the discovery questions:

  • What interference patterns does light make, and why?
  • What patterns do water waves make?
  • How can a complex wave be constructed from simple ones?
  • What do sounds "look" like?


There has to be a medium (something) for waves to travel through - this is true for sound waves, but not for electromagnetic waves (which includes light and UV radiation) which travel through the emptiness of space; this is another misconception: students think there's stuff in space.

All waves travel the same way - sound waves travel longitudinally (along the same direction as the wave), whereas water waves and light waves are transverse. Seismic waves (earthquakes) are more complicated.

Big waves travel slower (or faster) than small waves - how fast a wave travels is not dependent on the amplitude (height) of the wave (what students usually refer to when they speak of big or small), but it is related to the wavelength of the wave and the frequency of the wave. 2 waves of different amplitude can travel with the same speed - brighter and dimmer light.

The different colors of light are different waves (and are different than x-rays, UV rays) - the different colors of light are just electromagnetic waves with different specific wavelength/frequency. Frequency refers to how many wavelengths go past a reference point in a given time (or oscillate in the case of standing waves).

The wave is the same as the medium it is moving in - the wave refers to the movement of the particles within the medium (the water, slinky, etc.).

Learning Objectives

  • NGSS
    • Performance Expectations
      • HS-PS4-1. Use mathematical representations to support a claim regarding relationships among the frequency, wavelength, and speed of waves traveling in various media.
      • HS-PS4-3. Evaluate the claims, evidence, and reasoning behind behind the idea that electromagnetic radiation can be described either by a wave model or a particle model, and that for some situations one model is more useful than the other.
    • Disciplinary Core Ideas
      • HS-PS4: Waves and Their Applications in Technologies for Information Transfer
        • PS4.A: Wave Properties
          • The wavelength and frequency of a wave are related to one another by the speed of travel of the wave, which depends on the type of wave and the medium through which it is passing. (HS-PS4-1)
          • [From the 3–5 grade band endpoints] Waves can add or cancel one another as they cross, depending on their relative phase (i.e., relative position of peaks and troughs of the waves), but they emerge unaffected by each other. (Boundary: The discussion at this grade level is qualitative only; it can be based on the fact that two different sounds can pass a location in different directions without getting mixed up.) (HS-PS4-3)
        • PS4.B: Electromagnetic Radiation
          • Electromagnetic radiation (e.g., radio, microwaves, light) can be modeled as a wave of changing electric and magnetic fields or as particles called photons. The wave model is useful for explaining many features of electromagnetic radiation, and the particle model explains other features. (HS-PS4-3)
    • Practices
      • Developing and using models
        • Develop and/or use a model to predict and/or describe phenomena.
      • Using mathematics and computational thinking
        • Use mathematical representations to describe and/or support scientific conclusions and design solutions.
    • Crosscutting Concepts
      • Systems and system models
        • Students can understand that systems may interact with other systems; they may have sub-systems and be a part of larger complex systems. They can use models to represent systems and their interactions — such as inputs, processes and outputs — and energy, matter, and information flows within systems. They can also learn that models are limited in that they only represent certain aspects of the system under study.
  • NSES
    • NSES Physical Science – Interactions of energy and matter
      • Waves, including sound and seismic waves, waves on water, and light waves, have energy and can transfer energy when they interact with matter.
      • Electromagnetic waves include radio waves (the longest wavelength), microwaves, infrared radiation (radiant heat), visible light, ultraviolet radiation, x-rays, and gamma rays. The energy of electromagnetic waves is carried in packets whose magnitude is inversely proportional to the wavelength.

Discussion: Setting the Stage

  • What is light?

    The point of this is to brainstorm a list with students to see their thoughts. DO NOT give an answer until they have had a good discussion. Light is electromagnetic radiation. It sometimes behaves like a wave (which the first investigation will get into more depth) and sometimes like a particle.

  • Describe in your own words what a wave is and what it looks like.

    Students can even draw a wave. They will be learning answers to this during the simulations, so again, DO NOT give answers here.

Discussion: Formative Questions

  • What is the amplitude of the wave?

    The height of the wave.

  • What happens when I change the amplitude of a light wave?

    It gets brighter/dimmer.

  • What happens when I change the frequency of a light wave?

    It changes the color.

  • What looks different about the shape of the wave when I change the frequency?

    A higher frequency wave looks more compressed, a lower frequency wave looks more stretched out.

  • How many things should I be changing about the wave/light at one time?

    One thing at a time; otherwise I don't know which variable is affecting the wave/light.

  • What happens when I change the amplitude of a sound wave?

    It gets louder/softer.

  • What happens when I change the frequency of a sound wave?

    It changes the pitch.

  • What happens when a wave collides with another wave?

    It depends on the type of wave and how they interfere. If two peaks coincide, they add (constructive interference). If a peak coincides with a trough, they subtract (destructive interference).

  • What are some practical applications/uses for wave interference?

    Student answers will vary--this would generate some great discussion at the end.

Discussion: Wrapping Up

  • What is the relationship between wavelength and frequency?

    They are inverses - something with a short wavelength has a high frequency, something with a long wavelength has a low frequency.

  • What is the relationship between wavelength and amplitude?

    They are not dependent on each other.

  • What are some practical applications/uses for wave interference?

    Student answers will vary - this would generate some great discussion at the end.

Additional Background

There are two basic types of wave: longitudinal and transverse. Light and the wave motion of water and slinky are transverse waves (the wave moves perpendicular to the way it travels--the wave bumps move up and down while the wave travels left or right), while sound is a longitudinal wave (the compressed wave moves along the same direction of the wave).


Interference with Light

  1. Consider the formula: n lambda / d = x / L where: n = any integer lambda = wavelength; d = spacing between the sources x = spacing between the fringes; L = distance from source to screen. Ignoring the exact values of all the variables, see if your data confirms these two simple relationships:

    1. Holding everything else constant, the spacing between fringes (x) is proportional to the wavelength (lambda).
    2. Holding everything else constant, the spacing between fringes (x) is inversely proportional to the spacing between the sources (d).

    Explain your procedure for demonstrating that your data shows these relationships.

    Student answers should align with these and include evidence from their investigations. Answers to the second item will vary.

  2. The most common way to create a fixed spacing between sources of light is to use a diffraction grating, which is an opaque sheet (often plastic) with uniformly spaced scratches that let the light through. Each scratch becomes a "source," and if the spacing is uniform, it behaves like the two light sources in the model. You can also observe diffraction with light reflected off a CD. The lines act like slits, which in turn act like a row of evenly spaced emitters. Why do you think this diffraction surface would separate the different colors from each other, acting like a prism? (Hint: As the angle of the light reflecting from the CD surface changes, the apparent spacing of the lines changes.)

    Student answers will vary. The different colors of light are different wavelengths and so fit through/"hit" and bend at different angles (in different ways), thus separating the colors.

Ripple Tank

  1. Is the product of frequency and wavelength constant?

    Student answers will vary; they should be consistent with their snapshot albums

  2. What is the physical significance of this product? Note that its units are cm/s, since wavelength is measured in cm and frequency is measured in 1/s (drops per second).

    Student answers will vary; this product is the speed of the wave.

  3. Is the pattern for a single slit the same as the pattern for a single drop? Why?

    yes; it looks the same

  4. The ripple tank uses waves on the surface of water. Do you think interference would also be observed with other waves, such as sound and light? Why?

    Student answers should vary - this question is getting at what they think and would be awesome questions to discuss; the actual answer is yes--with light they saw this happen, and with sound, this is the appearance of "dead spots" in a room with speakers.

  5. Write out your own definitions of the following words: Reflection; Constructive Interference; Frequency; Wavelength; Amplitude

    Students answers should vary.

Taking Waves Apart

  1. Was it necessary to adjust the phase, or could you make a fit by just changing the proportions of overtones? (Answers may vary, some may need to have adjusted the phase; be sure student answer is consistent with their data.) Q: Do you think you could make a closer match if you had more overtones?

    Student will vary - it's what they think; Actual answer: yes.

  2. It has been shown mathematically that any repeated pattern, no matter how complex, can be represented as the combination of sine waves. Explain how this fact would allow the ear, which has hairs that are sensitive to a wide range of wavelengths, could distinguish between two sounds that have the same pitch.

    Each pitch has a distinct wavelength.

The Shape of Sound Waves

  1. For the following questions, use the drawing area to help explain your answer if necessary.

    For the picture there should two waves with the same height and different wavelengths

  2. Describe: Two different pitches with the same amplitude; Two notes with the same pitch but different amplitude.

    The note with the larger amplitude will be louder

  3. Describe: The wave pattern of a low pitch and a high pitch played at the same time

    Answers will vary - and would be more easily answered with a drawing; there will be places where the amplitudes will add, places where they will overlap and subtract - it will be less predictable, but may have shapes that suggest the two original waves.

  4. Describe: The wave pattern of "white noise"

    The wave pattern would have many different amplitudes and no distinguishable wavelength.

  5. Describe: The frequency graph of a pure note

    The frequency graph would be a straight horizontal note due to consistent frequency

  6. Describe: The frequency graph of a complex note where the first overtone is stronger than the basic pitch

    Answers will vary; The frequency of the first overtone would be higher on the graph than the basic pitch.

Further Investigation

Students could study standing waves, investigating phenomena like the Tacoma Narrows Bridge Collapse, why armies march intentionally out of step on bridges and such. Advanced students could be challenged to design a bridge or other structure to minimize the chance for standing waves and resonance.