The Doppler broadening of audio spectral lines is demonstrated using a simple experimental setup. The sound from a vibrating loudspeaker is received by a microphone that is connected to a computer sound card. A data-acquisition program is used to acquire the sound data. Fourier analysis is done to obtain the spectral power density of the sound received by the microphone. The results demonstrate spectral broadening similar to that which takes place in atomic and molecular spectroscopy. The experiment demonstrates both the Doppler effect and spectral broadening in the undergraduate physics lab.

Topics
Microphones, Structural beam vibrations, Acoustic transducers, Doppler effect, Data acquisition, Fourier analysis, Spectral methods, Atomic and molecular spectroscopy, Frequency spectrum, Educational aids
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© 2007 American Association of Physics Teachers.
2007
American Association of Physics Teachers
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