3.3 - Measuring the Speed of Sound

Measuring the speed of sound with an oscilloscope

• A signal generator connected to a speaker produces sound of a known frequency.
• Two microphones and an oscilloscope are used to find the wavelength of the sound, and from that the speed of sound in air.

Method

1. Connect a signal generator to a speaker. Place two microphones in front of the speaker, each connected to the oscilloscope so the sound at each microphone shows as a separate trace.
2. Start with both microphones next to the speaker, then slowly move one away until the two traces align again - exactly one wavelength apart.
3. Measure the distance between the two microphones to find the wavelength, $\lambda$.
4. Use $v=f\lambda$ to calculate the speed of sound.

The speed of sound in air is around 330 m/s, so the result should be close to this value.