28 terms

CH 20

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PLAY
How does a physicist usually define sound?
Sound can be defines as a disturbance in the air medium, which travels from one point to another point, causing sensation at the receiving end.
What is the relationship between frequency and pitch?
Frequency of an audible sound wave determines how high or low we perceive the sound to be, which is known as the pitch of sound.
What is the average range of a young person's hearing?
Average frequency range of audible sound waves varies from 20 to 20,000 Hz.
Distinguish between infrasonic and ultrasonic sound waves.
Infrasonic waves have lower frequency than audible sound, while ultrasonic waves have higher frequency than audible sound.
Distinguish between a compression and a rarefaction.
We observe compressions and rarefactions in longitudinal waves. At location of compression the molecules are crowded. So the density of this region increases and pressure in this region is high. At the location of the rarefaction molecules are away from each other. So, the density of this region decreases and pressure in this region is low.
Cite evidence to support the fact that compressions and rarefactions travel the same direction in wave.
Suppose we are in a long room. At one end is an open window with a curtain over it and at the other end, there is a door. As we continuously open and close the door, the curtain will move up and down. This shows that both compression and rarefaction travel in one direction.
Relative to solids and liquids, how does air rank as a conductor of sound?
Air is a poor conductor of sound compared to solids and liquids.
Why will sound not travel in a vacuum?
This is because sound waves require material mediums for their propagation.
What factors does the speed of sound depend upon? What are some factors that it does not depend upon?
The speed of sound depends upon many factors such as temperature, humidity, and wind conditions. The speed of sound is not dependent on frequency.
What is the speed of sound in dry air at 0C?
The speed of sound in dry air at 0C is approximately 330m/s.
Does sound travel faster in warm air than in cold air?
The speed of sound increases as temperature rises; thus, sound travels faster in warm air compared to cold air.
What is an echo?
An echo is reflected sound.
What is a reverberation?
Reverberation is the phenomenon in which sound continues to reflect off of boundaries such as the walls of a room.
What is the cause of refraction?
Refraction is caused due to variations of speed in different conditions, such as temperature or wind conditions.
Does sound tend to bend upward or downward when its speed is less near the ground?
In cold seasons, the layer of air near the ground is colder than the air above, which results in the reduction of the speed of sound near the ground. The high speed of the wave fronts above cause a bending of the sound downward toward the ground. This results in sound that can be heard over considerably longer distances.
Why does sound sometimes refract under water?
Sound sometimes refracts underwater due to temperature differences between the surface and under the water.
Which is normally greater, the energy in ordinary sound or the energy in ordinary light?
Energy of light is greater than energy of sound.
What ultimately becomes of the energy of sound in the air?
Sound energy dissipates to thermal energy while sound travels in air. High frequency sound waves are transformed into internal energy more rapidly than lower frequency waves. As a result, low frequency sound waves travel farther through the air than sounds at a higher frequency.
Why will a struck tuning fork sound louder when it is held against a table?
This is because the fork matches the frequency of the table that was set in motion and thus resonance takes place which leads to a louder sound.
Give at least two factors that determine the natural frequency of an object.
Shape of the object and elasticity property of the object.
How do forced vibrations relate to resonance?
Forced vibrations can be defined as the vibrations in which the body vibrates with a frequency other than its natural frequency under of action of an external periodic force. When an external frequency action on a body matches with its natural frequency, then the body starts to vibrate with maximum amplitude, this phenomenon is called resonance. A body that vibrates with maximum amplitude and said to be in resonance, if the natural frequency of a body coincides with the frequency of external periodic force.
When you listen to a radio, why do you hear only one station at a time rather than hearing all stations at once?
This is because when we choose a station, we ultimately select a particular frequency of sound and thus we hear only one sound rather than hearing all of the stations.
How did wind generated resonance affect the Tacoma Narrows Bridge in the state of Washington in 1940?
In 1940, four months after being completed, the Tacoma Bridge collapsed due to wind generated resonance. Due to resonance, an irregular force acted with the natural frequency of the bridge. As a result the amplitude of vibration increases until the bridge collapsed.
When is it possible for one wave to cancel another?
When the reflected wave is inverted and traveling in the opposite direction to that of the incoming wave. The reflected wave has the same amplitude as the incoming wave, and so it cancels the incoming wave out.
What kind of waves can exhibit interference?
Waves that have constant phase difference can exhibit interference.
What physical phenomenon underlies the production of beats?
Two sound waves which have slightly difference in frequency and they are traveling in same direction. These two sound waves will get interference. The constructive interference yields the maximum loudness of sound and the deconstructive interference yields minimum loudness of sound. This periodic variation of loudness of sound is called as beats. Thus interference is the physical phenomenon that involves in the production of beats.
What beat frequency will occur when a 370-Hz and a 374 Hz sound are sounded together?
Beat frequency is given by
=n_1 - n_2
=374-370
=4Hz
How does a radio wave differ from a sound wave?
A radio wave is an electromagnetic wave, while a sound wave is a mechanical wave. The speed of a radio wave is much faster than the speed of a sound wave.
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