1. As he has a fair knowledge of English he reads scientific articles without a dictionary. 2. As the physicist took a great interest in this substance he regarded its properties in detail. 3. As he

knows the subject perfectly well he is always ready to help his friends with it. 4. As they were aware of the peculiarities of this substance they treated it carefully. 5. As I thought he was busy I

didn't disturb him. 6. As these liquids have very similar properties they may be considered together. 7. As these values lack precision they can't be used in our calculations.

Light

The nature of light. Scientists have always been puzzled by the nature of light. In the seventeenth century there were two schools of thought concerning it. Isaac Newton regarded light as a stream of corpuscles or tiny particles traveling in straight lines, whilst the Dutch physicist Huygens held that light consisted of waves in a substance called the “ether”, which he supposed filled the whole space including that between the atoms of matter and which could not be removed even from a vacuum.

As time went on and more became known about the behaviour of light, Huygens’ wave theory came to be accepted as the better one. At present, however, we have evidence to suppose that light consists of streams of tiny wave-like packets of energy called “quanta”, which travel at a speed of 186000 miles per second.

Atoms emit light at high temperatures produced by chemical reaction in a flame, by the electrical heating of thin tungsten wire in the ordinary electric lamp or by the bombardment of gas molecules by electrons in a discharge lamp tube.

Sources of light. The sun is the chief source of light and heat, but there are many artificial sources. Any body when heated to a sufficient high temperature becomes a source of light. As the temperature of a body is raised, the body emits invisible radiations. When it becomes red-hot, visible radiations begin to be emitted. The higher the temperature, the greater is the amount of both heat and light waves that are emitted, but the percentage of visible radiations becomes larger as the temperature of the source of radiations is increased.

Ex.1. Make up some questions to the text

Ex.2. Make up and write 8 sentences using these words.

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

is becomes became

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

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

Ex. 4. 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.

Ex. 5. 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 that 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. 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.