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3. Frequency is measured in units of 14. Two out-of-phase sound waves with the same amplitude and
a. time. frequency arrive at the same place at the same time, resulting in
b. cycles. a. a beat.
c. hertz. b. cancellation of the two sound waves.
d. avis. c. a lower frequency.
4. The maximum displacement from rest to the crest or from rest to d. the bouncing of one wave.
the trough of a wave is called 15. Two sound waves of equal amplitude with slightly different
a. wavelength. frequencies will result in
b. period. a. an echo.
c. equilibrium position. b. the Doppler effect.
d. amplitude. c. alternation of loudness of sound known as beats.
5. A wave with motion perpendicular to the direction that the wave d. two separate sounds.
is moving is classified as a 16. Two sound waves of unequal amplitudes with different
a. longitudinal wave. frequencies will result in
b. transverse wave. a. an echo.
c. water wave. b. the Doppler effect.
d. compression wave. c. alternation of loudness known as beats.
6. Your brain interprets a frequency as a sound with a certain d. two separate sounds.
a. speed. 17. The energy of a sound wave is proportional to the rate of energy
b. loudness. transferred to an area perpendicular to the waves, which is called
c. pitch. the sound
d. harmonic. a. intensity.
7. Sound waves with frequencies greater than 20,000 Hz are b. loudness.
a. infrasonic waves. c. amplitude.
b. supersonic waves. d. decibel.
c. ultrasonic waves. 18. A decibel noise level of 40 would be most likely found
d. impossible. a. during a calm day in the forest.
8. Generally, sounds travel faster in b. on a typical day in the library.
a. solids. c. in heavy street traffic.
b. liquids. d. next to a pneumatic drill.
c. gases. 19. A resonant condition occurs when
d. vacuums. a. an external force matches a natural frequency.
9. Sounds travel faster in b. a beat is heard.
a. warmer air. c. two out-of-phase waves have the same frequency.
b. cooler air. d. a pure tone is created.
c. Temperature does not influence the speed of sound. 20. The fundamental frequency of a string is the
d. a vacuum. a. shortest wavelength harmonic possible on the string.
10. The bending of a wave front between boundaries is b. longest standing wave that can fit on the string.
a. reflection. c. highest frequency possible on the string.
b. reverberation. d. shortest wavelength that can fit on the string.
c. refraction. 21. The fundamental frequency on a vibrating string is what part of
d. dispersion. a wavelength?
11. A reflected sound that reaches the ear within 0.1 s after the a. 1/4
original sound results in b. 1/2
a. an echo. c. 1
b. reverberation. d. 2
c. refraction. 22. Higher resonant frequencies that occur at the same time as the
d. confusion. fundamental frequency are called
12. The wave front of a refracted sound bends toward a. standing waves.
a. warmer air. b. confined waves.
b. cooler air. c. oscillations.
c. the sky, no matter what the air temperature. d. overtones.
d. the surface of Earth, no matter what the air temperature. 23. A moving source of sound or a moving observer experiences the
13. Two in-phase sound waves with the same amplitude and apparent shift in frequency called
frequency arrive at the same place at the same time, resulting in a. fundamental frequency.
a. higher frequency. b. Doppler effect.
b. refraction. c. wave front effect.
c. a new sound wave with greater amplitude. d. shock waves.
d. reflection.

5-21 CHAPTER 5 Wave Motions and Sound 135