Christian Doppler proposed the phenomenon in 1842 for light waves.
In 1845 Dutch scientist Christoph Buys-Ballot developed a test for the Doppler shift of sound.
A trumpet player sounded a note at 420 Hz while riding on a flatcar pulled by a locomotive. At the same time a stationary trumpeter played the same note. Buys-Ballot heard 3.5 beats per second. How fast was the train moving?
REFLECTION – WATER WAVES
REFLECTION – SOUND WAVES
Signaling Mirror: A life-saving application of reflection
How would you use a signaling mirror if you were in a lifeboat trying to attract attention from a passing airplane?
See training film at: www.youtube.com/watch?v=avmnRrCVBaP0
(To construct your own signaling mirror see: www.youtube.com/watch?v=lTy-o5Ci4-k)
(Index of refraction is a measure of how much waves are slowed down)
Note the important difference between the spectra produced by a prism and by a grating:
In spectra produced by a prism, violet light (shorter wavelength) is refracted through a greater angle than red light (longer wavelength). In spectra produced by a grating, however, red light is diffracted through a greater angle than violet light.
White light seen through a 2-D grating (from UNSW online demonstrations)
DIFFRACTION OF WATER WAVES
Assignment for Wednesday: Read Chapter 4 Homework: Exercises 1,3,4,5,7,8,10 (p.58) Extra credit: Write a short essay showing how the signaling mirror works (with diagrams). More extra credit: Construct a signaling mirror and demonstrate it to the class.
More extra credit:
Read the article “Outdoor Sound Propagation in the U.S. Civil War (ECHOES 9, Winter 1999) and write a brief report.