Physics Help >> Index to Physics Homework Help » Sound and Hearing

1. A guitar string of length, L, is fixed at both ends. Which of the following wavelengths for standing waves is

not possible on this string?
a. L/2 b. 2L/3 c. L d. 2L e. 4L

2. Pipe A is 30.0 cm long and is closed at one end, open at the other. Pipe B is open at both ends. How long will pipe B have to be to have the same fundamental frequency as pipe A?

3. Two speakers, one directly behind the other, are each generating a 256-Hz wave. What is the smallest separation distance between the speakers that will produce destructive interference at a listener standing in front of them? Take the speed of sound to be 342 m/s.

4. A middle-aged man typically has poorer hearing than a middle-aged woman. In one case a woman can just begin to hear a musical tone, while a man can just begin to hear the tone only when its intensity level in increased by 6.8 dB relative to that for the woman. What is the ratio of the intensity just detected by the man to that just detected by the woman?

5. A rock is dropped from a sea cliff and the sound of it striking the ocean is heard 3.4s later. If the speed of sound is 340 m/s, how high is the cliff?

6. Why is the loudness directly proportional to the logarithm of intensity?

7. A jouse is 32000 times greater in power than a voice. By how many decibels is the factory noise greater than the voice?

ANSWERS

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2.

60.0 cm

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7. A decibel is one tenth of a bel, where a bel is logarithmic ratio of two intensities.

Intensity = 10log(I₁ / I₀) (dB)

In this case,

I = 10log(32000 / 1 ) = 45

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