Lab Instructions Objective: To determine the speed of sound in air. Method: The speed of sound is
Question:
Lab Instructions
Objective: To determine the speed of sound in air.
Method: The speed of sound is a very important number. It determines the pitch of wind instruments, the time lag for echoes, and is important in the acoustics of concert halls.
We will send sound waves down a pipe by clapping near the pipe's end. The sound travels down the pipe and reflects from the other end of the pipe. The WavePad app on a cell phone will be used to detect this returning sound wave and show a graph of it on the screen. The up and down line on the graph screen shows variation in air pressure in the sound wave. (Note that the sound wave will reflect from the far end even though this is an open end.)
The graph on the phone screen will show a large response when the sound wave is first created and passes by the phone's microphone as it enters the pipe and later another large response when it arrives back after reflecting. The sound wave then reflects at the end with the phone and goes back down the pipe again and reflects again. This way we see multiple peaks each time the sound wave returns to the phone as the wave "bounces" back and forth. The time scale in the app, given in milliseconds (ms), will allow us to measure the time that it takes the sound wave to move down the pipe and return. Knowing the distance traveled and the time of travel, we can calculate speed.
To see the very quick rise and decline of sound waves, we will need to expand the time scale, spreading out the wave so we can see the details of detection and reflection. To allow enough time separation between the waves, we need a pipe that is at least 10 feet long.
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