Standing Waves

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Objective

Students construct an explanation for how standing waves form using wave vocabulary words.

Big Idea

Standing waves form when an incident wave interferes with a reflected waves to form nodes and anti-nodes.

Context and Supplies

Due to standardized state testing, we have a half-day today so the class period is only 30 minutes long. In the previous class, Slinky Rules, students learn about interference and wave reflection. Now they apply that understanding to explain how standing waves form. They use a simulation to explore the creation of a standing wave and then use wave vocabulary to construct an explanation. Computers for students and a standing wave demonstrator are needed for this lesson.

To complete this lesson, students apply CCSS Math Practice 5: Use appropriate tools strategically and Math Practice 7: Look for and make use of structure. As they develop an explanation for how standing waves form, they apply NGSS Science Practice 2: Developing and using models and Science Practice 6: Constructing explanations. The NGSS Performance standards applied are HS-PS4-1: Use mathematical representations to support a claim regarding relationships among the frequency, wavelength, and speed of waves traveling in various media and HS-PS4-5: Communicate technical information about how some technological devices use the principles of wave behavior and wave interactions with matter to transmit and capture information and energy.

Standing Wave Simulation

25 minutes

Students learn that waves interfere constructively and destructively in Slinky Rules. Now they learn how about standing waves. I tell the students that without standing waves, music and musical instruments would not exist. A sustained musical note is not possible without the formation of a standing wave. Today they explore the concept of standing waves and construct an explanation of how they form.

The standard seating for my students is groups of 4 students at two tables pushed together. Since time is short today, I have students work with one of the partners at their desk. Each partnership gets a computer and a copy of the Standing Wave Activity which students fill out in pairs. The handout has students navigate to Walter Fendt's webpage of physics Java programs (http://www.walter-fendt.de/ph14e), scroll down to the "Oscillations and Waves" section and open Standing Wave (Explanation by Superposition with the Reflected Wave) Java program. This program shows an incoming periodic wave that reflects off of a barrier, which I discuss in Standing Wave Java Demo. As this happens, students see a standing wave form with nodes and anti-nodes. They construct an explanation of how a standing wave forms using wave vocabulary words such as constructive interference, destructive interference, incident, and reflected waves.

After this, students navigate to The Physics Classroom page on Standing Wave Formation and use the information there to check if their explanation of how a standing wave forms matches what is on the Physics Classroom page. While students work on the activity, I invite groups up to observe the standing wave generator I have set up at the front of the room. It is important to expose students to real-life examples as much as possible so that they know what is described in the textbooks is true. At the end of class, I collect student work to check for understanding.

Big Ideas on Waves Homework

For homework, students are to complete a Socrative quiz Intro to Waves - Big Ideas; though it is a quiz, this counts as a homework grade.  Socrative is a great tool that allows students to answer questions using their smart phones or computers and the program grades the results.  The goal of this homework is to reinforce the big ideas of the unit that have been explored so far. Those are:

1. The velocity of a wave is determined by the medium.

2. The frequency of a wave is determined by the wave source.

3. The wavelength is a result of the frequency and velocity according to the wave equation.

4. The amplitude of a wave is determined by the energy of a wave.

5. The amplitudes of separate waves add together when waves interfere.

During the next class period, we review the quiz using Intro to Waves - Big Ideas Solutions.