Ch 26 Chapter Review Q & A’s
Q: What is the source of all sounds?
A: vibrating objects
Q: How does pitch relate to frequency?
A: Pitch is subjective, but it increases as frequency increases
Q: What is the average frequency range of a young person’s hearing?
A: 20 Hz – 20,000 Hz
Q: Distinguish between infrasonic and ultrasonic sound.
A: Infrasonic – below 20 Hz and ultrasonic – above 20,000 Hz
Q: Distinguish between compressions and rarefactions of a sound wave
A: Compressions are regions of high pressure & rarefactions are regions of low pressure
Q: How are compressions and rarefactions produced?
A: Compressions & rarefactions are produced by a vibrating source.
Q: What evidence can you cite to support the statement: Light can travel in a vacuum.
A: you can see the sun or the moon
Q: Can sound travel through a vacuum?
A: No, sound needs a medium to travel
Q: How does air temperature affect the speed of sound?
A: Sound travels faster at higher temperatures.
Q: How does the speed of sound in air compare with its speed in water & in steel?
A: Sound travels faster in water & faster again in steel
Q: Why does sound travel faster in solids an dliquids than in gases?
A: The atoms are closer together, & solids and liquids are more elastic mediums
Q: Why is sound louder when a vibrating source is held to a sounding board?
A: More surface is forced to vibrate and push more air.
Q: Why do different objects make different sounds when dropped on a floor?
A: They have different natural frequencies.
Q: What does it mean to say that everything has a natural frequency of vibration?
A: The natural frequency is characteristic of the object’s shape, size, & composition.
Q: What is the relationship between forced vibration and resonance?
A: Resonance is forced vibration at the natural frequency.
Q: Why can a tuning fork or bell be set into resonance, while tissue paper cannot?
A: Tissue paper has no natural frequency.
Q: How is resonance produced in a vibrating object?
A: By input of vibrations at a frequency that matches the natural frequency of the object
Q: What does tuning in a radio station have to do with resonance?
A: By input of vibrations at a frequency that matches the natural frequency of the objects
Q: Is it possible for one sound wave to cancel another? Explain
A: Yes, it is destructive interference
Q: Why does destructive interference occur when the path lengths from two identical
sources differ by half a wavelength?
A: The crests of one coincide with the troughs of the other; canceling each other out.
Q: How does interfernce of sound relate to beats?
A: Beats are a result of periodic interference.
Q: What is the beat frequency when a 494 Hz tuning fork & a 496 Hz tuning fork are
sounded together? And what is the frequency of the tone heard?
A: beat frequency (496 – 494) Hz = 2 Hz
tone heard is half way between 495Hz
Q: When watching a baseball game, we often hear the bat hitting the ball after we
actually see the hit. Why?
A: Light travels faster than sound
Q: What 2 physics mistakes occurin a movie when you see & hear at the same time
a distant explosion in outer space?
A: Distant sound should get to you after you see the light. Also, sound cannot travel in a
vacuum, so there would be not sounds transmitted in out space.
Q: Why will marchers at the end of a long parade following a band be out of step with
marchers nearer the band?
A: There is a time delay for sound from a marching band near the front of a long parade
to reach the marchers at the end.
Q: When a sound wave propagates past a point in the air, what are the changes that occur
in the pressure of air a this point?
A: Air pressure increases and decreases at a rate equal to the frequency of the sound
wave
Q: If the handle of a tuning fork is held solidly against a table, the sound becomes louder.
Why?
A: More surface vibrates and more air is pushed
Q: If the handle of a tuning fork is held solidly against a table, the sound becomes louder.
How will this affect the length of the time the fork keeps vibrating?
A: The time decreases because more sound energy is sent out so the tuning fork loses
energy more rapidy.
Q: What beat frequency would occur if two tuning forks ( 260 Hz & 266 Hz) are
sounded together?
A: 263 Hz
Q: Two notes are sounding, one of which is 440 Hz. If a beat frequency of 5Hz is heard,
what is the other notes’s frequency?
A: Either 445 Hz or 435 Hz
Q: Two sounds, one at 240 Hz and the other at 243 Hz., occur at the same time. What
beat frequency do you hear?
A: (243 Hz- 240 Hz) = 3Hz
Q: A longitudinal wave can also be called a ___ wave.
A: a compression wave
Q: A wave that resembles a transverse wave but occurs in mediums that are
fixed at both ends is call a ___ wave.
A: a standing wave
Q: When a wave is incident on a medium boundary and changes its direction due
to a change in the wave’s velocity, this wave behavior is called ___.
A: refraction
Q: When a wave encounters an obstacle in its path and spreads out (bends) around the
obstacle, this wave behavior is called ___.
A: diffraction
Q: The ___ of a sound wave depends on how much the matter carrying the wave is
compressed by each vibration.
A: amplitude
Q: true or false The frequency of a sound wave is the same as the frequency of the
vibration that produces the sound.
A: True
Q: Ultrasounds are sounds found above the ___Hz mark.
A: Ultrasounds are above 20,000 Hz.
Q: The pitch of a train whistle appears to ___ as it approaches & ___ as it travels
away from an observer.
A: pitch appears to increase as it approaches and decrease as it moves away
Q: The field of study that analyzes the behavior of waves is called ___.
A: acoustics
Q: The multiple reflections of a sound wave is called ___.
A: reverberation
Q: true or false
The greater the amount of energy created by a wave, the larger its
amplitude.
A: true
Q: The intensity of sound is measured in ___.
A: decibels
Q: What 3 things can you do to a guitar string to decrease its frequency & pitch?
A: Make the string 1. longer
2. thicker
3. decrease tension of string (loosen string)
Q: When a wave changes from a straight wavefront to a curved front, this is called __.
A: diffraction
Q: This term refers to waves of the same frequency that are either in phase or out of
phase of each other.
A: interference