Lesson three

Notes

1. Isn't it a small world – Мир тесен.

2.occurrences in nature – явления в природе

3. things or events that at first seem to have nothing to do with... – предметы или события, которые, как кажется на первый взгляд, ничего не имеют общего...

III. Say whether the following statements are true or false:

1. These seven types of rays do not differ from each other. 2. Seven kinds of rays are close relatives. 3. We find three types of invisible rays in use in our homes. 4. We meet three types of rays outside the home. 5. These seven types of rays differ from each other in their frequency. 6. The frequency is the number of cycles in a second. 7. Radio waves have the highest frequency.

IV. Find the information explaining why we call light a visible ray. Read the information to your partner.

V. 1) Answer the questions on paragraph 3:

1. What rays do we deal with when we listen to a radio programme? 2. How are infrared rays referred to sometimes? 3. What rays do we use when we sit under a sun-tan lamp? 4. What kind of rays can we find inside the hospital? 5. Are microwaves used with radar equipment?

2) Name the types of invisible rays we find in use: a) in our homes-, b) outside the home.

VI. In paragraph 4 find the English equivalents to the following words:

луч, тип, частота, расстояние, напоминать, длина волны, период, полный (законченный), двигаться, называть, длинный, низкий, количество.

VII. Speak about the electromagnetic waves using English words from the logical diagram.

VIII. Fill in the boxes of the following logical diagram with English equivalents.

IX. Say briefly what each paragraph is about.

		частота		длина волн
				электромагнитные волны

X. Read paragraph 4 again and say what makes the seven rays different from each other.

I. Look through the list of the English words and their Russian equivalents for better understanding text B:

subtle – тонкий, неуловимый; to occur – происходить; to convert – преобразовывать; receptive – восприимчивый; beyond – за пределами; wavelength – длина волны; to range – колебаться в пределах; frequency – частота; to approach – приближаться; beam – пучок; луч; to fan out – расходиться, распространяться.

II. Read text В. Find out the main information of the text.

Text В

Radio Waves

During the last few decades, a subtle change has occurred which none of our senses¹ can register. Radio waves, bearing messages in many tongues², flow ceaselessly around us, through us and above us. We can only hear and see them if we convert them to other waves to which our ears and eyes are receptive.

Radio waves are the longest members of the family of electromagnetic waves. In the spectrum, in which the waves are arranged in order of increasing wavelength³, they lie beyond the infrared waves. Their wavelengths range from about three hundredths of a centimetre to about 300 kilometers. Radio broadcasts today are made by two different methods known as AM (amplitude modulation) and FM (frequency modulation). The frequencies of the waves used are expressed in kilocycles or megacycles. The vibrating current is fed into an antenna from which the radio waves are broadcast into space.

Microwaves are the smallest radio waves. In the spectrum of electromagnetic waves they lie between infrared rays and the long radio waves. The shortest microwaves have a wavelength of about three hundredths of a centimetre and a frequency of one million megacycles. The longest microwaves have a wavelength of about three metres and a frequency of one hundred megacycles.

The first microwaves made by man were the two-foot waves produced by Heinrich Hertz. It is interesting that they were the last to be put to a practical use. Long waves were easier to produce and send out over long distances. Scientists had to return to the use of short waves in order to solve a problem⁴ that came up during World War II. The problem was "How can you detect an approaching enemy plane while it is still far away? " A possible answer to the problem was to send a beam of radio waves. Long radio waves could not be used for this purpose because they fan out too quickly from the broadcasting antenna. Very short waves were necessary to make the radar system work. So new transmitters and receivers were designed to make and use microwaves.

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