Answers to the Production and Properties of Sound
by
Cynthia D'Souza

This lesson was created as a part of the SMART website and is hosted by the Illinois Institute of Technology

1. The velocity of sound in air is --------- to ambient temperature at any set atmospheric pressure.

A. directly proportional

2. If air pressure remains constant and temperature rises, the speed of sound

B.  rises

3. A French experiment carried out in the 18th century determined the speed of sound by measuring the time, over a fixed distance, between

C.  the flash and boom of cannons

4. The speed of sound at human body temperature (37oC) is

D. 354 m/s  [(331.5m/sec + (0.6m/secoC)(37oC)) = 353.7m/sec]

5. During a sound check, the technician at a rock concert adjusted a circuit to hear the sound from the stage through the air at the same time he could hear it through his headphones. The afternoon temperature was 30oC,  the evening performance was 13oC, and the soundboard was 200 m from the stage. How much of a delay did the technician hear at the evening performance?

A. 0.02 s  [Using the equation from #4, the speed at 30oC is 349m/sec for a time of  about 0.57s and at 13oC the speed is 339m/sec and the time is 0.59s]

6. A Concorde jet flies at Mach 1.2 at an altitude of approximately 10 km (speed of sound + 1050 km/h), and a normal jet flies at 600 km/h. How much faster does the Concorde fly than a normal jet?

B.  more than twice as fast  [1.2 x 1050km/hr = 1260km/hr]

7. The threshold of hearing is considered to be

C.  0dB

8. The threshold of hearing is defined by an intensity of 10-12 W/m2.   A conversation has a measured intensity of 10-5W/m2. The intensity in decibels is

A. 70  [log10 of difference times 10 to get dB]

9. A jet airplane passing a quiet restaurant produces a sound intensity of 75 dB. The sound intensity at the restaurant is 45 dB. The motorcycle noise is roughly -----more intense than the sound in the restaurant

C.  1000 times [divide the difference in intensity by ten and raise 10 to that power. i.e.  (75 - 45)/10 = 3 then the answer is 103]

10. The  outer ear

A. directs sound to the eardrum and helps determine sound direction.

11. The middle ear consists of the

C. hammer, anvil and stirrup

12. The human ear is most sensitive to sounds in the range of

A.   2000-4000 Hz

13.Because the sensitivity of the human ear varies over the audio spectrum, many sound systems----- very high and ----very low frequencies to compensate.

B. amplify, amplify

14. A room with a reverberation of zero is called

A. an anechoic chamber

15. The ability of waves to travel round obstacles or through small openings is  called

D. diffraction

16. Waves with longer wavelengths diffract---- waves with shorter wavelengths

C. more than

17. Because lower notes are more easily diffracted by openings and objects than higher notes, it is usually -----to determine the source of ---- notes

B. harder, lower

18. At night, when a layer of cool air is close to the ground and warmer air is above, sound tends to

A. refract back towards the ground

19. A stone is dropped into a well that is 100 m deep. The temperature is 25oC. How much time elapses between the moment when the stone is dropped and the moment when the sound of the stone hitting the bottom is heard?

C. 4.8 s  [4.5 s to fall, 0.3 s for the sound to return]

20. A boat race is started by a cannon blast on the shore. the ships are perpendicular to the shore where the cannon is placed. the muzzle flash cannot be seen. If the nearest ship is 0.5 km from the cannon and the farthest ship is 1.0 km from the cannon, how much sooner does the nearest ship hear the cannon, if the temperature is 15oC.

B. 1.5 s  [0.5km = 500m and the speed of sound at 15oC is 340m/sec.]

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