Passage: All of us listen to some or other type of music. We also hear the news and other programs on the radio. Most of us take sound for granted, and not once do we wonder how and where sound comes from. Let us try to understand sound. Sound is any disturbance that can travel through a m

Question

Passage: All of us listen to some or other type of music. We also hear the news and other programs on the radio. Most of us take sound for granted, and not once do we wonder how and where sound comes from. Let us try to understand sound. Sound is any disturbance that can travel through a medium like air or water and then be heard by the human ear. When a body vibrates, the vibration conducts a periodic disturbance in the surrounding air or any other medium and causes sound. These disturbances are pressure waves. It means the vibration leads to periodic pressure changes in the medium. Suppose you have a guitar with you and you pluck one of its strings. It does produce sound; how does it do so? The movement of the strings in one direction pushes the molecules of the air just before it. This produces crowding of the molecules in that region. And when the string moves back from its original position, it leaves behind a space with a smaller number of molecules. In other words, the vibratory motion set up by the guitar string causes, alternately in space, a crowding together of the molecules of air (a condensation) and an emptying out of the molecules (a rarefaction). Taken together, a condensation and a rarefaction make up a sound wave. This kind of wave is called longitudinal, because the vibratory motion is forward and backward along the direction that the energy wave is following. Because such a wave travels by disturbing the molecules, a medium is absolutely essential for sound waves to travel. We know that sound waves cannot travel through vacuum. How is it that we hear these sound waves? The vibrations or condensation and rarefaction cause sufficient vibrations on our eardrums for our brains to hear them. Our ears do not hear all the vibrations. Sound is generally audible to the ear if the frequency (number of vibrations per second) of sound waves lies between 20 and 2000 vibrations per second. The range varies from one individual to another. Sound waves with frequencies less than those of audible waves are called subsonic; those with frequencies above the audible range are called ultrasonic. Now one can ask how fast these vibrations travel. Well, the velocity of sound is not a constant. It is different for different media. In the same medium, the velocity of sound is different at different temperatures. Sound travels more slowly in liquids than in solids. Since the ability to conduct sound is dependent on the density of the medium, solids are better conductors than liquids; liquids are better conductors than gases. Normally the speed of sound is considered to be 344 meters per second. Sound waves can be reflected, refracted and absorbed as light waves can be. An echo is a reflection of sound with sufficient strength that arrives at the listener with an appropriate delay after the direct sound so that it can be clearly heard. If a sound wave returns within 1/10 sec, the human ear is incapable of distinguishing it from the original one. Which of the following is similar in meaning to “conducts” as highlighted in the passage?

Accepted Answer

supervise. In the passage, “conducts” means “carries” or “transmits” a disturbance through a medium. Among the options, “supervise” is the closest in the sense of directing or carrying out an activity, while the others do not fit the context.

Solution

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