Beats, Electromagnetic Waves, and something else for dessert....

First, some web-based toys to simulate beats and other bits of interference:

http://www.mta.ca/faculty/science/physics/suren/Beats/Beats.html
See two sine waves added together.

http://micro.magnet.fsu.edu/primer/java/interference/waveinteractions2/index.html
Phase Difference Demo

http://library.thinkquest.org/19537/java/Beats.html
Simulation of beats that you can hear!

Second, the table of data you must use for calculating the speed of sound from today's experiment:


Third: Some solutions to the problems from today's homework set:

Chapter 12:
44. The unknown whistle has to be HIGHER than the 23.5 kHz if it is to be inaudible to humans. Humans can hear up to around 20 kHz. This means the whistle frequency must be 23.5 Khz + 5 kHz = 28.5 kHz.

53. 77.27 Hz is the frequency observed by the stationary tuba player - it is higher by the Doppler effect. The beat frequency would be 2.27 Hz.

54. This problem can be figured out in much the same way as 53, just with the actual frequency of the horn as the unknown. If the stationary frequency is F_o, the higher frequency perceived by the stationary observer must be (340/325)*F_o.

The equation (340/325)*F_o - F_o = 5.5 Hz will allow you to determine the actual frequency of 120 Hz. The two frequencies would be 120 Hz and 126 Hz, the 126 Hz observed from the moving car. Thus the frequency of both horns must be 120 Hz.