1. It becomes red-hot, it is the reason, it was cold...

The sun is the chief of light. It was cold. The percentage of visible radiations becomes larger.

2. High temperature produced by..., in a substance called... . Exercises

1. Listen, read and translate the text.

2. Answer the following questions in a written form:

1. How many schools of thought concerning the nature of light were there in the 17th century? 2. Who were the leaders of these schools? 3. At what conditions do the atoms emit light? 4. When does a body become a source of light? 5. When can tungsten be heated to a high temperature?

3. Make up and write 8 sentences using the words given in the table:

Any body heated in a flame The percentage of visible radiations The modern tung­sten lamp It Her voice More

is becomes became

a source of light. red-hot. larger. much more efficient. known about the behaviour of light. louder.

4. Copy these sentences putting "light", "has puzzled", "evidence", "emit", "streams", "tungsten" in the blanks: 1. We have ... to suppose that light consists of... of quan­ta. 2. His invention ... the scientists by its simplicity.

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3. The study of ... was Newton's favourite study. 4. Atoms ... light at high temperatures. 5. ... has a very high melting point.

5. Translate the following sentences and explain the use of participles:

1. If a ringing bell is touched with the fingers, the sound ceases because, the vibrations are stopped by the fingers. 2. If a stretched guitar string is plucked, it gives a musical note owing to the vibrations set up in it. 3. This method is an extensive of that used by him. 4. This law takes into ac­count forms of energy other than those discussed so far. 5. The wave length so determined will not be exactly accurate.

6. Sound waves may be reflected, producing echoes.

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

1. Sounds differ in intensity, loudness, pitch and quality. 2. Intensity is a measure of energy of the sound waves. 3. Loud-ness is the effect which a sound has on our ear. 4.Pitch depends only upon the number of vibrations that reach the ear per second.

7. Translate the following sentences and explain the use of tenses in them:

1. Objects which are seen by the light which they themselves produce are said to be luminous. 2. Things which glow because of their high temperatures are said to be incandes­cent. 3. These objects are said to produce cold light. 4. Some objects can emit light without the requirement of a high temperature. 5. Most objects are not seen by the light they them­selves emit. 6. They are non-luminous and are seen by the light which falls on them from some luminous source, such as the sun, and which is then scattered or reflected towards our eyes. 7. The element helium was discovered to be a con­stituent of the sun from a detailed study of sunlight well before this rare gas was identified on the earth. 8. According to modern ideas light, in common with the other forms of electromagnetic radiation, is given out in the form of waves and spreads outwards from its source like ripples on the sur­face of a pond, but in every direction — not just in two di­mensions. 9. The waves in heat radiation are longer than those in light, but this difference in the size of the waves is fundamentally the only difference between them.

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8. Make up and write 10 questions to the above sentences.

9. Make up and write complex sentences using the simple sentences given in the table (e.g. I shall go home when I finish my work):

The sound will cease. A guitar string will give a musical note. They will be in the library. There will be some effects.

if as soon as when until

A ringing bell will be touched. It will be plucked. They will finish their lessons. They will make experiments. Light will strike matter.