1. It does not move forward but returns again...

The jerk moves forward, but the particles of the rope move only up and down. The rooms were dark, but the streets were lighter because of their lamps.

2. It is evident, it is clear.

It is evident that he is a good student. It is clear that they will go to the stadium.

Exercises

1. Listen, read and translate the text.

2. Answer the following questions in a written form:

1. How is energy transmitted? 2. Where does each particle of the rope impart its upward and downward motion to? 3. How does the jerk move? 4. What does the tension in the string tend to do? 5. When can a wave travel along the string with a definite velocity? 6. Where are transverse waves easily produced? 7. What waves are known as transverse waves?

3. Make up and write 6 compound sentences using the simple sentences given in the table: (e.g. She did not come to me but she visited my friend.)

The jerk moves forward. The water does not really move outward from the central point. It does not move forward. The room was dark. I had had no news of her in the hospital. She wanted to come to see me.

but

It rises and then falls again. It returns again and again to its former position. The particles of the rope move only up and down. The street was lighter be­cause of its lamps. She has been so busy. She wrote to my friend.

4. Translate the sentences into Russian paying special at­tention to the different meanings of the verb "to be":

1. One of the most important phenomena in nature is the transmission of energy from one point to another by wave motion. 2. This kind of

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motion is illustrated in many waves. 3. He is in the laboratory. 4. He is making an experiment now. 5. They are to study some material about sound. 6. The masses in the two pans will then be equal. 7. His aim is to study this material. 8. Many hydroelectric power stations were built in our country. 9. This view has been supported by a number of experiments. 10. There have been many theo­ries to explain the nature of heat. 11. Heat was considered to be an invisible substance. 12. Electrical energy can be transformed into heat energy.

5. Make up and write complex sentences using the simple sentences given in the table: (e.g. It is clear that he is a good student.)

It is evident It is not clear It is usual

that where whether

there is a vibrating centre. he will do it. they made an experiment. the jerk travels down the rope. the waves can travel along the string with a definite velo­city. the string has inertia.

6. Copy these sentences putting "transverse", "vibrations", "waves" "electromagnetic", in the blanks:

1. A wave which is propagated by ... perpendicular to the direction of travel of the wave is called a ... wave. 2. Examples of transverse ... are waves on strings and water. 3. ... waves which include light waves are transverse waves.

7. Make up and write all possible questions to the follow­ing sentences:

1. In contrast to a transverse wave, a longitudinal wave is one in which the vibrations occur in the same direction as the direction of travel of the wave. 2. The displacements of the particles cause regions of high density and of low den­sity to be formed. 3. These regions move along with the speed of the wave.

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Laboratory Exercises

8. Listen and read the following word combinations:

wave motion, transmission of energy, circular wavelets, a floating leaf, each jerk, position of equilibrium, definite velocity, lightly stretched, transverse waves, represented by plotting, the vertical axis, horizontal axis, electromagnetic waves, excellent illustrations.

9. Listen and repeat in pauses:

Transmission of energy from one point to another by wave motion is one of the most important phenomena in nature. When you drop a stone into water, the surface of it is cov­ered with circular wavelets. The water does not really move outward from the central point, but rises and then falls again. Each particle of the rope imparts its upward or downward motion to its neighbours. The jerk moves forward, but the particles of the rope move only up and down. A wave which is propagated by vibrations perpendicular to the direction of travel of the wave is called a transverse wave.

10. Listen to these questions on the above text and answer them:

1. What is one of the important phenomena in nature? 2. When is the surface of water covered with circular wavelets? 3. How does the jerk move? 4. How do the particles of the rope move?

11. Ask questions using the model.

Model : Each jerk travels along the rope.

Where does each jerk travel?

1. Each portion of the rope communicates the jerk to the next portion. 2. Each particle of the rope imparts its upward or downward motion to its neighbours. 3. A vibrating centre produces motion in portions of the medium. 4. The jerk moves forward along the rope.

12. Listen to this short dialogue and learn it by heart:

— In nature there exists the transmission of energy by wave motion. So, a wave allows energy to be transferred, doesn't it?

— Yes, it does. A wave carrying energy travels along the medium from one point to another.

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— All right. For example, sound waves carry energy from the source to the ear by disturbance of the air.

— Yes, you are right. And now, would you, please, tell me about particles of air.

— Particles of air actually travel in the process.

-- What sound waves are there in nature?

-- There are some of them. For example, a wave which is propagated by vibrations perpendicular to the direction of travel of the wave is called a transverse wave.

— I am sorry, but I don't remember the definition of a longitudinal wave. Will you be so kind to give it?

— Of course. In contrast to a transverse wave a longitu­dinal wave is one in which the vibrations occur in the same direction as the direction of travel of the wave.

13. Suggested topics for oral narration:

1. State, with reason, whether the following waves are transverse or longitudinal: water waves, the waves traveling along the string, in a rope. Draw sketches to illustrate your answer.

2. State and explain the difference between transverse and longitudinal waves.