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Chapter 12: Q3MCQ (page 328)
The sound level near a noisy air conditioner is 70 dB. If two such units operate side by side, the sound level near them would be
(a) 70 dB.
(b) 73 dB.
(c) 105 dB.
(d) 140 dB.
The correct option is (b).
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If two firecrackers produce a combined sound level of 85 dB when fired simultaneously at a certain place, what will be the sound level if only one is exploded? [Hint: Add intensities, not dBs.]
Question: (I) (a) What resonant frequency would you expect from blowing across the top of an empty soda bottle that is 24 cm deep, if you assumed it was a closed tube? (b) How would that change if it was one-third full of soda?
Question: (III) (a) Expensive amplifier A is rated at 220 W, while the more modest amplifier B is rated at 45 W. (a) Estimate the sound level in decibels you would expect at a point 3.5 m from a loudspeaker connected in turn to each amp. (b) Will the expensive amp sound twice as loud as the cheaper one?
A fish finder uses a sonar device that sends 20,000 Hz sound pulses downward from the bottom of the boat, and then detects echoes. If the maximum depth for which it is designed to work is 85 m, what is the minimum time between pulses (in fresh water)?
Sound waves are
(a) transverse waves characterized by the displacement of
air molecules.
(b) longitudinal waves characterized by the displacement
of air molecules.
(c) longitudinal waves characterized by pressure
differences.
(d) Both (b) and (c).
(e) (a), (b), and (c).
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