Supersonic waves

The word "supersonic" means moving faster than sound. Sound waves travel with a definite speed in any elastic medium. A vibrating source of sound acts on the surrounding particles of the medium, creating compressions and rarefactions that spread out in alternate sequence through the whole area of the medium. The number of compressions and rarefactions following one another in the course of a second determine the pitch at which a sound is heard.

The human ear can register sounds to about 20,000 vibrations per second. Nature, however, has a much greater range of sounds than that. Science discovered the existence of these frequencies in the last century. They were called supersonic, and a method was worked out to produce them in laboratory conditions. At present, scientists in various countries are successfully creating instruments emitting supersonic waves of great intensity at frequencies of several hundred million vibrations per second.

One of the excellent properties of supersonic waves is their ability of penetrating metals, alloys and other materials to a great depth. With the help of supersonic detectors we can discover cavities, cracks and other internal faults in metal and ceramics at the depth of over 30 feet. The faults reflect supersonic waves that are recorded on the screen of an oscillograph in the form of an impulse indicating the position of the faults. By means of a supersonic apparatus the thickness of any ob can be measured with great accuracy. Special supersonic e sounders on board a ship help to determine the exact depth of sea, on every yard of the ship's course, underwater, rocks, reefs, and icebergs being discovered in the same way.

Supersonic waves may also be used to bore holes in hard brittle metals. Moreover, they are used of in breaking up and crushing various substances to produce fine emulsions of liquids and me such emulsions being now widely employed in different industries.

Supersonic waves are very sensitive, their speed changing if a medium contains even a small quantity of foreign matter. Special instruments having been constructed on this basis, it became possible to control chemical reactions and technological processes with great precision.

Under the influence of supersonic waves the minute particles of a hard substance in a gaseous medium join together, forming larger particles that fall out of the medium. This principle forms the basis of a method of cleaning smoky air.

Scientists are working on problems connected with the physical nature of supersonic waves and their application in science and everyday life. It is to be hoped that in a few years from now this will bring us many discoveries of still greater importance.

IX. Translate the text in written form synoptically.

RADAR

The word "radar" means Radio Determination and Ranging. Radar equipment is capable of determining by radio echoes the presence of objects, their direction, range and recognizing their character.

There are several types of radar sets, all of them consisting of six essential components, namely: a transmitter, a receiver, an antenna system, and an indicator), a timer, and, of course, a power supply.

A radar set detects objects by sending out short powerful pulses of ultrahigh frequency radio wave energy from a highpower transmitter. The directional antenna takes this energy from the transmitter and radiates it in a beam (similar to that of a searchlight).

As the transmitted energy strikes an object, a portion of it is reflected back. The receiver picks up the returning echo through its antenna and translates it into visual readable signals on a fluorescent screen. The appearance of these signals shows the presence of an object within the field of view of radar.

The electron beam sweeps across the fluorescent screen in somewhat the same way as a hand sweeps across the face of a clock. Just as the hand of a clock completes its sweep in sixty seconds, the electron beam can be made to travel across any desired portion of the screen in some predetermined interval of time. It is the timer, which is the synchronizer of the whole system, that times the transmitter pulse and the indicator. The use of these timed pulses and the fact that the radio waves travel at the constant velocity of light gives a simple means of measuring range. The accuracy with which time is measured determines the accuracy of the range.

How then is the direction in which an object lies to be found? Both azimuth and elevation can be determined by means of the directional antenna. The antenna may be rotated as the pulses are sent out and the strongest signal appears on the screen when the antenna points directly at the object. The direction of the antenna enables the determination of azimuth and elevation. Thus, with the help of a radar set we can get a three-dimensional location of an object.

The wide use of radar sets in our everyday life will make air and sea entirely safe. Radars may be installed on every ship at sea as well as in every large harbour. They will prevent collisions in fog and aid a ship to sail safely into any harbour, regardless of night or weather. Similarly airplanes will be able to fly over mountain ranges in storms and effect blind landing during poor visibility.

X. Translate the text in written form synoptically.

SEMICONDUCTORS¹

The term "semiconductor¹" means "half-conductor", that is, a material whose conductivity² ranges between³ that of conductors and non-conductors or insulators.

They include great variety of elements (silicon, germanium, selenium, phosphorus and others), many chemical compounds (oxides⁴, sulphides⁵) as well as numerous ores⁶ and minerals.

While the conductivity of metals is very little influenced by temperature, conductivity of semiconductors sharply increases with heating and falls with cooling. This dependence has opened great prospects for employing semiconductors in measuring techniques.

Light, as well as heat, increases the conductivity of semiconducting materials, this principle being used in creating photo resistances. It is also widely applied for switching on engines, for counting parts on a conveyer belt, as well as various systems of emergency signals⁷ and for reproducing sound in cinematography. Besides reacting to light, semi-conductors react to all kinds of radiations and they are therefore employing in designing electronic counters.

Engineers and physicists turned their attention⁸ to semiconductors more than fifty years ago, seeing in them the way of solving complicated engineering problems. Converting heat into electricity without using boilers or other machines was one of them. This could be done as means of metal thermocouples, but in this way impossible to convert more one per cent of the heat into electricity. The thermocouples made later of conductors more generated ten times as much electricity as the metal ones.

Sunlight like heat can feed our electric circuit. Photocells made of semiconducting materials are capable of transforming ten per cent; of sunray energy into electric power. By burning wood, which has accumulated the same amount of solar energy, we obtained only heat fractions of one per cent of electric power.

The electricity generated by semiconductor thermocouples can produce not only heat but also cold, this principle being used in, manufacturing refrigerators.

Semiconducting materials are also excellent means of maintaining a constant temperature irrespective of the surrounding temperature changes. The latter can vary over a wide range, for example, from 50° below 0° to 100° above 0°.

Semiconductors are the youngest field of physical science. Yet even now they are determining the progress of radio engineering, automation, chemistry, electrical engineering and many other fields of science and technique.