Measurement of the Velocity of Sound through Resonance in Air Columns as a Homemade Experiment

In recent years, with the more powerful functions of smartphones, the use of sensors integrated by mobile phones as an auxiliary tool for physical experiment teaching has become more popular. Combined with the related mobile phone apps, people easily can develop and expand the physical experiment contents of mechanics, optics, acoustic phenomena, and so on. These experiments not only help students master the relevant laws of physics, but also permit or encourage students to carry out experimental research, greatly increase students' interest in learning, and meet the training requirements of the Next Generation Science Standards. Recently, some experiments about measurement of speed of sound have been introduced. It is amazing and interesting that people can use simple tools to measure the speed of sound.­ This kind of experiment is very helpful to improve students' practical ability in experiment design, data acquisition, and analysis. Inspired by the above experiments, especially the Kundt's tube experiment, we demonstrate the acoustic resonance in an air column using a plastic tube, a mobile phone, a loudspeaker, and a tape measure. Through the resonance phenomenon of an air column, the speed of sound in air can be calculated conveniently. The experimental results are in good agreement with the reference value. This kind of homemade experiment can provide guidance for students to carry out relevant research in a non-laboratory environment.