# Warm-Up Exercise for lecture 26

## Due 8:00 am, Thurs, 3 Dec 09

Physics 105, Fall 2009

What happens when two pulses on a string (one coming from each end) meet in the middle?
☑ The pulses pass through each other
☐ The pulses reflect off of each other

If a loudspeaker emits spherical sound waves in all directions, what decreases as you go farther away from the loudspeaker?
☐ frequency
☑ intensity
☐ wavelength

You go to a rock concert where the sound level where you are standing is 110 dB. How does the intensity (power/area) of sound waves compare to when you listen to the same music on your home stereo system, 90 dB at the spot you sit?
☐ Concert intensity = Stereo intensity
☐ Concert intensity = 1.20x stereo intensity
☐ Concert intensity = 2x stereo intensity
☐ Concert intensity = 10x stereo intensity
☐ Concert intensity = 20x stereo intensity
☑ Concert intensity = 100x stereo intensity

Ralph is confused about Table 14.2 (8th edition), where the book lists different intensity levels for different sources. For example, the table says a vacuum cleaner has an intensity of 70 dB. What confuses Ralph, is that it seems like a vacuum cleaner should sound louder to someone who is pushing the vacuum cleaner than to someone who is a little farther away. How can the intensity level be 70 dB for both people? How should you answer Ralph's question?
For once in his life, Ralph is correct! The table should really specify *where* the sound level is 70 dB. Presumably that is the vacuum cleaner operator, so someone farther away will hear a lower sound level--perhaps 60-65 dB, depending on where the person is located.