Physics 8: Homework 5 Additional Questions



In addition to the problems from the book (11.E.16, 11.E.19, 12.E.13, 12.E.14, 12.E.14, 12.E.15, 12.E.16, 12.E.17), here are more problems that are a required part of the assignment:

  1. Make up a set of self-consistent numbers describing a sound wave in air. These numbers should include frequency, period, wavelength, and speed. The only restriction is that they describe a wave that the human ear could hear. Are there any other numbers relevant to a sound wave?
  2. Noise cancelling headsets work by producing sound that is 180° out of phase with the ambient sound waves so that when added together, you're left with nothing (destructive interference). Given that the electronics have to sample the ambient pressure amplitude, send a signal to the speaker, and get the speaker to move fast enough to cancel the sound before the ambient amplitude (pressure) changes much, why do you think these headsets are better at canceling low frequencies, and cease to work at high frequencies?
  3. A sound source of 80 dB is ten times louder than a sound of 70 dB. How much louder is 90 dB compared to 70 dB?
  4. For low frequencies, we rely on the tiny difference in arrival time between our two ears to localize the direction of sound sources. But underwater we are unable to sense direction of sound. Why do you think this is?
  5. Why is it that a 100 Hz sine wave sounds like a low, soft tone, but a square wave at the same frequency (100 Hz) sounds buzzy/raspy? Think frequency content.
  6. On a CD, which are more important for carrying information: the pits, or the non-pits, or both equally. Explain your answer.


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