Ultrasonic sounds produce pulsed signals ____various defects in metal can be detectedA.for

The range in frequencies of musical sounds is approximately 20- 20,000 cycles per second (cy/sec), Some people can hear higher frequencies than others. Longitudinal waves whose frequencies are higher than those within the audible range are called ultrasonic frequencies. Ultrasonic frequencies are used in sonar for such purposes as submarine detection and depth finding. Ultrasonic frequencies are also being tried for sterilizing food since these frequencies kill some bacteria. Sound waves of all frequencies in the audible range travel at the same speed in the same medium. In the audible range, the higher the frequency of the sound the higher is the pitch. The term supersonic refers to speed greater than sound. An airplane traveling at supersonic speed is moving at a speed greater than the speed of sound in air at that temperature. Mach 1 means a speed equal to that of sound. Mach 2 means a speed equal to twice that of sound, etc.

Musical sounds have three basic characteristics; pitch, loudness, and quality or timbre. As was indicated above, pitch is determined largely by the frequency of the wave reaching the ear. The higher the frequency the higher is the pitch. Loudness depends on the amplitude of the wave reaching the ear. For a given frequency, the greater the amplitude of the wave the louder the sound. To discuss quality of sound we need to clarify the concept of overtones. Sounds are produced by vibrating objects. If these objects are given a gentle push, they usually vibrate at one definite frequency producing a pure tone. This is the way a tuning fork is usually used. When objects vibrate freely after a force is momentarily applied, they are said to produce their natural frequency. Some objects, like strings and air columns, can vibrate naturally at more than one frequency at a time. The lowest frequency which an object can produce when vibrating freely is known as the object's fundamental frequency. Other frequencies that the object can produce are known as its overtones. The quality of a sound depends on the number and relative amplitude of the overtones present in the wave reaching the ear.

A soprano would probably have a frequency of ______.

A．200 cy/sec

B．5,000 cy/sec

C．10,000 cy/sec

D．20,000 cy/sec

Radar (雷达)

1. Children enjoy shouting at a high wall and hearing the sound come back to them. These sounds are called echoes (回声). Echoes have given us a number of 'valuable tools.

2. Echo sounding devices were early used in making maps of the ocean floor. Sounds or Ultrasonic (超声的) sounds make good tools for determining how deep the water is under ships. Sometimes echoes from ultrasonic distance finding devices were prevented from working by fish swimming past or by the presence of large objects. So ultrasonic devices have been replaced by other tools.

3. Radar is now a familiar tool. Like many others it was ah unexpected discovery. It was first observed by two researchers, who were studying sound communication. They were sending signals from a station on one side of a river in Washington, D .C. to a vehicle across the river. They discovered that their signals were stopped by passing ships. They recognized the importance of this discovery at once.

4. All this was of course just a start, from which our present radar has developed. The word "radar," in fact, gets its name from the term "radio detection (检测) and ranging." "Ranging" is the term for detection of the distance between an object and the radar set. Today, in our scientific age, it would be difficult to manage without radar.

5. One of the many uses of radar is as a speed control device on highways. When a person in an automobile is driving faster than the speed limit, radar will show this clearly and the traffic police can take measures to stop him.

6. A pilot cannot fly a plane by sight alone. Many conditions such as flying at night and landing in dense fog require the pilot to use radar. Human eyes are not very good at determining speeds of approaching objects, but radar can show the pi lot how fast nearby planes are moving.

A Study of Sound

B Highway Police

C Working Principles

D Early Use of "Radar"

E Useful Tools

F Discovery by Chance

Paragraph 2 ______

The range in frequencies of musical sounds is approximately 20-20,000 cycles per second (cy/sec). Some people can hear higher frequencies khan others. Longitudinal waves whose frequencies are higher than those within the audible range are called ultrasonic frequencies. Ultrasonic frequencies are used in sonar for such purposes as submarine detection and depth finding. Ultrasonic frequencies are also being tried for sterilizing food since these frequencies kill some bacteria. Sound waves of all frequencies in the audible range travel at the same speed in the same medium. In the audible range, the higher the frequency of the sound the higher is the pitch. The term supersonic refers to speed greater than sound. An airplane traveling at supersonic speed is moving at a speed greater than the speed of sound in air at that temperature. Mach 1 means a speed equal to that of sound. Mach 2 means a speed equal to twice that of sound, etc.

Musical sounds have three basic characteristics: pitch, loudness, and quality or timbre. As was indicated above, pitch is determined largely by the frequency of the wave reaching the ear. The higher the frequency the higher is the pitch. Loudness depends on the amplitude of the wave reaching the ear. For a given frequency, the greater the amplitude of the wave the louder the sound. To discuss quality of sound we need to clarify the concept of overtones. Sounds are produced by vibrating objects. If these objects are given a gentle push, they usually vibrate at one definite frequency producing a pure tone. This is the way a tuning fork is usually used. When objects vibrate freely after a force is momentarily applied, they are said to produce their natural frequency. Some objects, like strings and air columns, can vibrate naturally at more than one frequency at a time. The lowest frequency which an object can produce when vibrating freely is known as the object's fundamental frequency. Other frequencies that the object can produce are known as its overtones. The quality of a sound depends on the number and relative amplitude of the overtones present in the wave reaching the ear.

A soprano would probably have a frequency of ______.

A．200 cy/see

B．5,000 cy/sec

C．10,000 cy/sec

D．20,000 cy/sec

Radar (雷达)

1. Children enjoy shouting at a high wall and hearing the sound come back to them. These sounds are called echoes (回声). Echoes have given us a number of 'valuable tools.

2. Echo sounding devices were early used in making maps of the ocean floor. Sounds or Ultrasonic (超声的) sounds make good tools for determining how deep the water is under ships. Sometimes echoes from ultrasonic distance finding devices were prevented from working by fish swimming past or by the presence of large objects. So ultrasonic devices have been replaced by other tools.

3. Radar is now a familiar tool. Like many others it was ah unexpected discovery. It was first observed by two researchers, who were studying sound communication. They were sending signals from a station on one side of a river in Washington, D .C. to a vehicle across the river. They discovered that their signals were stopped by passing ships. They recognized the importance of this discovery at once.

4. All this was of course just a start, from which our present radar has developed. The word "radar," in fact, gets its name from the term "radio detection (检测) and ranging." "Ranging" is the term for detection of the distance between an object and the radar set. Today, in our scientific age, it would be difficult to manage without radar.

5. One of the many uses of radar is as a speed control device on highways. When a person in an automobile is driving faster than the speed limit, radar will show this clearly and the traffic police can take measures to stop him.

6. A pilot cannot fly a plane by sight alone. Many conditions such as flying at night and landing in dense fog require the pilot to use radar. Human eyes are not very good at determining speeds of approaching objects, but radar can show the pi lot how fast nearby planes are moving.

A Study of Sound

B Highway Police

C Working Principles

D Early Use of "Radar"

E Useful Tools

F Discovery by Chance

Paragraph 2 ______

West, and China is now riding the experimental tide. More than 80 parents of children with severe mental disabilities have booked all of next years spots in the program.(Sessions only run in the summer because the water temperatures are too cold for the kids in other seasons.)However, newcomers must wait until 2014, says Liu【M1】______ Quansheng, manager of the parks owner, Zhejiang Aquarium Investment Group. Despite of the demand, dolphin-assisted therapy has not been 【M2】______ scientifically proven. Still, many experts and parents of special-needs children swear in it. While the science of dolphin-assisted therapys 【M3】______ assortment of purported benefits hasnt been verified, many believe at least some benefits come from the experiences emotional magic. "Once the children are in the pool theyre only focused on the dolphins. They love it, because the creatures let the kids touch and kiss them, grab their fins and swim with them." Most opponents agree on the merit of the fun factor. Some also 【M4】______ claim it boost peoples immune systems. And many experts contend the【M5】______ therapys benefits run deeper. Dolphins presence palpably changes water. Those which swim with the creatures report fizzing sounds, as if【M6】______ the marine mammals carbonate the water. The sound has been compared as popcorn, flames and sparklers. The marine animals 【M7】______ ultrasonic energy is four times powerful than scientific instruments 【M8】______ using to peer inside the body to make diagnoses, monitor pregnancies 【M9】______ and break in kidney stones, gallstones and cataract-clouded lenses. This【M10】______ is amplified by the water, which transmits sounds at 60 times airs efficiency. The ultrasonic energy then enters our bodies — which are, in turn, mostly water. But how — and if — this helps children with mental disabilities remains unclear.

【M1】

earing is far more acute. Sounds which most others would miss can carry a great deal of information to a sightless person. For instance, teams of blind children can enjoy fast-moving games of soccer with a bell inside the ball and a new hand-held ultrasonic device to guide them. And that sound-location system could help to build up an even more complete sound picture of a blind person's surroundings.

Bats, whose sight is poor, use a sound-location system to help them avoid obstacles in the dark. They send out pulses of sound waves, pitched at 50,000 cycles per second, far above the limits of the human ear, which can hear sounds up to frequencies of about 20,000 cycles per second. As the echoes bounce back off obstacles such as trees and walls, the bats are able to take appropriate action.

The first steps to help blind people to see with sound are based on exactly the same principle. The sound is emitted by an ultrasonic torch, shaped like a double-barreled version of a normal electric torch. It works in a similar Way to a sonar u nit on a warship or submarine.

The unit’s transmitter sends out pulses of ultrasonic waves at the same frequency as the bat, and the receiver picks up the returning echoes. Because these are still above the frequency at which the human ear can pick them up, the echoes are filtered through circuits which turn them into clearly audible ' bleeps' before passing them into headphones.

This means that a person holding the torch can point it ahead of him and ‘scan’the area for obstacles over a range of about 25 ft. ff there are no return echoes coming through the headphones, then there is nothing in the way.

If echoes do come back, then the closer the obstruction, the faster the succession of bleeps and the deeper the pitch of each bleep. With practice the torch could help a blind person to lead a more normal life -- without needing a constant companion to guide him. Experienced operators of the torch system claim they can distinguish grass from bushes, trees, pests and curbstones.

But before blind people can be helped to feel really independent, the system needs to be more streamlined. At pres ent, the experimental ultrasonic torch requires a shoulder bag to carry the batteries, cables for the power supplies and earphones, in addition to the torch itself. But miniaturization of electronic equipment is making such rapid progress that it should not be long before the whole set-up can be reproduced in a form. small enough to fit into a pair of spectacles.

The transmitter and power supplies, with all the circuitry, would be packed into the bridge-piece above the nose. The sending and receiving sensors would be in the ' lenses'. And the filtered bleeps would be passed on to the wearer through the earpieces, as with present-day hearing-aid spectacles.

This would mean that scanning one’s surroundings would become instinctive. The wearer would face in the direction he wanted to check, and lift or lower his head just as a sighted person would.

How do blind children play soccer？

A．They listen to the sound of the ball bouncing.

B．They ask an adult to guide them.

C．They hold a bell in their hands.

D．They put a bell inside the ball.

Dolphin-assisted therapy for children with mental disabilities has made a splash in the West, and China is now riding the experimental tide. More than 80 parents of children with severe mental disabilities have booked all of next years spots in the program.(Sessions only run in the summer because the water temperatures are too cold for the kids in other seasons.)However, newcomers must wait until 2014, says Liu【M1】______ Quansheng, manager of the parks owner, Zhejiang Aquarium Investment Group. Despite of the demand, dolphin-assisted therapy has not been 【M2】______ scientifically proven. Still, many experts and parents of special-needs children swear in it. While the science of dolphin-assisted therapys 【M3】______ assortment of purported benefits hasnt been verified, many believe at least some benefits come from the experiences emotional magic. "Once the children are in the pool theyre only focused on the dolphins. They love it, because the creatures let the kids touch and kiss them, grab their fins and swim with them." Most opponents agree on the merit of the fun factor. Some also 【M4】______ claim it boost peoples immune systems. And many experts contend the【M5】______ therapys benefits run deeper. Dolphins presence palpably changes water. Those which swim with the creatures report fizzing sounds, as if【M6】______ the marine mammals carbonate the water. The sound has been compared as popcorn, flames and sparklers. The marine animals 【M7】______ ultrasonic energy is four times powerful than scientific instruments 【M8】______ using to peer inside the body to make diagnoses, monitor pregnancies 【M9】______ and break in kidney stones, gallstones and cataract-clouded lenses. This【M10】______ is amplified by the water, which transmits sounds at 60 times airs efficiency. The ultrasonic energy then enters our bodies — which are, in turn, mostly water. But how — and if — this helps children with mental disabilities remains unclear.

【M1】

earing is far more acute. Sounds which most others would miss can carry a great deal of information to a sightless person. For instance, teams of blind children can enjoy fast-moving games of soccer with a bell inside the ball and a new hand-held ultrasonic device to guide them. And that sound-location system could help to build up an even more complete sound picture of a blind per-son's surroundings.

Bats, whose sight is poor, use a sound-location system to help them avoid obstacles in the dark. They send out pulses of sound waves, pitched at 50,000 cycles per second, far above the limits of the human ear, which can hear sounds up to frequencies of about 20,000 cycles per second. As the echoes bounce back off obstacles such as trees and walls, the bats are able to take appropriate action.

The first steps to help blind people to see with sound are based on exactly the same principle. The sound is emitted by an ultrasonic torch, shaped like a double-barreled version of a normal electric torch. It works in a similar way to a sonar unit on a warship or submarine.

The unit’s transmitter sends out pulses of ultrasonic waves at the same frequency as the bat, and the receiver picks up the returning echoes. Because these are still above the frequency at which the human ear can pick them up, the echoes are filtered through circuits which turn them into clearly audible bleeps before passing them into headphones.

This means that a person holding the torch can point it ahead of him and scan the area for obstacles over a range of a-bout 25 ft. If there are no return echoes coming through the headphones, then there is nothing in the way.

If echoes do come back, then the closer the obstruction, the faster the succession of bleeps and the deeper the pitch of each bleep. With practice the torch could help a blind person to lead a more normal life——without needing a constant companion to guide him. Experienced operators of the torch system claim they can distinguish grass from bushes, trees, pests and curbstones.

But before blind people can be helped to feel really independent, the system needs to be more streamlined. At present, the experimental ultrasonic torch requires a shoulder bag to carry the batteries, cables for the power supplies and earphones, in addition to the torch itself. But miniaturization of electronic equipment is making such rapid progress that it should not be long before the whole set-up can be reproduced in a form. small enough to fit into a pair of spectacles.

The transmitter and power supplies, with all the circuitry, would be packed into the bridge-piece above the nose. The sending and receiving sensors would be in the 'lenses'. And the filtered bleeps would be passed on to the wearer through the earpieces, as with present-day hearing-aid spectacles.

This would mean that scanning one's surroundings would become instinctive. The wearer would face in the direction he wanted to check, and lift or lower his head just as a sighted person would.

How do blind children play soccer？

A．They listen to the sound of the ball bouncing.

B．They ask an adult to guide them.

C．They hold a bell in their hands.

D．They put a bell inside the ball.

听力原文： The vast oceans of the world are dark, deep and mysterious places where eyesight counts for little as soon as you venture very far beneath the surface.

For humans, who live in a world dominated by visual stimuli, to exist in such conditions would be impossible. But for whales and dolphins that live in the ocean or, in the case of a few species, muddy rivers, the darkness is unimportant. What is important to them is sound.

Sound is an efficient way to transmit and sense information, especially as it travels five times faster through water than through air. If humans shout to someone, it is unlikely that they will be heard a kilometer away. But if a whale shouts in an ocean channel, another whale may hear it tens, if not hundreds, of kilometers away.

Whales and dolphins use sound in two ways: for communication and for echolocation. Dolphins and toothed whales communicate through a wide variety of high-frequency sounds.

But as well as using sounds to communicate, toothed whales and dolphins also rely on echolocation to learn about their immediate environment, including prey that might be waiting nearby. They produce intense short broad-band pulses of sound in the ultrasonic range. These clicks are brief, typically less than one millisecond long—but they are repeated many times each second.

(4)

A．Sense of sight.

B．Sense of hearing.

C．Sense of smell.

D．Sense of taste.