Lesson: Standing Waves Physics • 9th Grade

In this lesson, we will learn how to describe the structures of standing waves that can form by resonance with objects of different lengths.

Lesson Plan

Students will be able to

recall that a traveling wave that reflects at a boundary changes its phase by radians,
recall that a standing wave is formed by the superposition of a traveling wave directed toward a boundary and the reflected wave from the boundary,
recognize that for a standing sound wave in a pipe, the amplitude of the wave must be zero at the closed end of the pipe,
recognize that for a standing sound wave in a pipe, the amplitude of the wave must be at its maximum at the open end of the pipe,
recognize that for a pipe of length that is open at one end, the standing sound waves that can exist in the pipe have wavelengths given by , where is an odd integer,
recognize that for a pipe of length that is open at both ends, the standing sound waves that can exist in the pipe have wavelengths given by , where is an integer.

Lesson Worksheet

Q1:

A pipe that is open at both ends is 2.4 m long. What is the wavelength of a sound wave that has a frequency equal to the pipe’s fundamental frequency?

Q2:

A pipe that is closed at one end has a fundamental frequency of 48 Hz. The speed of sound in the air inside the pipe is 343 m/s. Find the length of the pipe. Give your answer to one decimal place.

Q3:

A pipe that is closed at one end is 0.35 m long. What is the wavelength of a sound wave that has a frequency equal to the pipe’s fundamental frequency?