Chapter 17: Q5CQ (page 628)
Is the Doppler shift real or just a sensory illusion?
Doppler effect is not an illusion it is a real phenomenon.
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(a) Ear trumpets were never very common, but they did aid people with hearing losses by gathering sound over a large area and concentrating it on the smaller area of the eardrum. What decibel increase does an ear trumpet produce if its sound gathering area is\(900\;{\rm{c}}{{\rm{m}}^{\rm{2}}}\)and the area of the eardrum is\(0.500\;{\rm{c}}{{\rm{m}}^{\rm{2}}}\), but the trumpet only has an efficiency of\(5.00\% \)in transmitting the sound to the eardrum? (b) Comment on the usefulness of the decibel increase found in part (a)
What length should an oboe have to produce a fundamental frequency of 110 Hz on a day when the speed of sound is 343 m/s? It is open at both ends.
If a woman needs an amplification of \({\rm{5 \times 1}}{{\rm{0}}^{{\rm{12}}}}{\rm{ W}} \cdot {{\rm{m}}^{{\rm{ - 2}}}}\) times the threshold intensity to enable her to hear at all frequencies, what is her overall hearing loss in dB? Note that smaller amplification is appropriate for more intense sounds to avoid further damage to her hearing from levels above\({\rm{90 dB}}\).
Suppose a bat uses sound echoes to locate its insect prey, \(3.00m\) away.
(a) Calculate the echo times for temperatures of \(5.00\;{\rm{^\circ C}}\) and \(35.0\;{\rm{^\circ C}}\).
(b) What percent uncertainty does this cause for the bat in locating the insect?
(c) Discuss the significance of this uncertainty and whether it could cause difficulties for the bat. (In practice, the bat continues to use sound as it closes in, eliminating most of any difficulties imposed by this and other effects, such as motion of the prey.).
If audible sound follows a rule of thumb similar to that for ultrasound, in terms of its absorption, would you expect the high or low frequencies from your neighbor’s stereo to penetrate into your house? How does this expectation compare with your experience?
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