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