Ultraviolet and infrared

Visible light covers a very small part of the electromagnetic spectrum. Just above and below the visible light range are ultraviolet and infrared light. The " ultra" in ultraviolet tells us that this light lies at frequencies higher than that of violet light lies; and the " infra" in infrared tells us that this light lies at frequencies lower than red.

Ultraviolet has a shorter, and infrared has longer wave lengths than visible light. The radiations were discovered long before anyone thought of electromagnetism. When light was passed through a prism and formed a spectrum on screen, scientists found that heating effect occur beyond the edges of the visible light spectrum.

Ultraviolet radiation produces many effects, some useful and some unpleasant. A certain amount of ultraviolet radiation is good for our health. It helps to form vitamin D in the skin. Ultraviolet light also kills microbes, and for that reason it is used in hospitals and to sterilize food.

Direct ultraviolet radiation is very bad for the eyes. This is one reason why it is dangerous to look directly at the sun. On the other hand, the human eye is quite capable of dealing with normal doses of scattered ultraviolet light.

Infrared energy is being used in automatic regulation of chemical and biological processes, temperature measurement and control during manufacture of textiles, plastics and metals. New applications are appearing in navigation and aviation, weather research numerous scientific projects.

Other applications for infrared are found in photography aerial mapping, communications and control techniques.

Infrared energy is in use all around us. Infrared techniques are of great value in many industrial applications and are considered indispensable in many others. The possibilities of its application appear to be limited only by the imagination and skill of the user.

RADAR

Electromagnetic waves is the super high frequency range, that is waves of between about 1 and 10 centimeters in length, are reflected by large solid object in much the same manner as light. They are however, able to travel greater distances than light in the Earth's atmosphere, because they are not reflected or diffused by small dust particles in the atmosphere. If, therefore, a transmitter sends out a beam of these centimeter waves, an adjacent receiver can be make to pick up any of the beam that is reflected back by a large solid object. In this way distant object that are not visible by light can be located. By suitable scanning arrangements, the position and shape of the object can be outlined on a cathode ray tube. Thus, electromagnetic waves of these frequencies, which are called radar frequencies, provide a method of " seeing" in the dark or in the fog.

1. Without electronic equipment space flights would be impossible. 2. It is required that natural piezo (pai'izou) electric crystals of quartz should be used in radio broadcasting transmitters. 3. Without quantum electronics these instruments could not be developed. 4. Modern complex controls can perform functions which man would not be able to carry out. 5. The engineer suggested this photographic cell should be used for measuring temperature. 6. Everything might have been solved long ago.

Ответьте на вопросы по тексту:

1. What is the Earth?

2. How fast is the Earth?

3. When do we have night and day?

4. How fast does the Earth travel around the Sun?

5. What seasons does the Earth have?

6. Where are ultraviolet and infrared light?

7. Where are ultraviolet and infrared energies used?