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Warm-Up Exercise for lecture 26

Due 8:00 am, Thurs, 3 Dec 09

Physics 105, Fall 2009

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Did you complete the reading assignment? (Typically this means at least 20-30 minutes looking over the assigned sections of the book.)
☐ yes ☐ no

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?

The comments in the next next two boxes go into a big, mostly anonymous text file that I skim through before the morning lecture, using the comments to help me plan class discussion. ("Mostly anonymous", because I can track down who made what comment, but it takes some effort on my part to do so.) Therefore, if you really want to make sure I see your question/comment and answer it individually, you should send it to me via email and not through this form.

Which part of today's assignment was particularly hard or confusing? What would you like to spend extra time on in class?

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