Контрольная работа по Английскому языку на тему: "Перевод текста"

WEATHERING

Variations in temperature from day to night and from winter to summer cause expansion and contraction of rock material. Occasionally these changes are known to cause mechanical failure of rock. But it still seems unlikely that temperature changes are great enough to cause extensive mechanical weathering. Theoretically, such changes in temperature should cause disintegration. For example, we know different materials which form a granite to expand and contract at different rates as they react to rising and falling temperatures. We would expect, then, that even minor expansion and contraction of adjacent minerals would, over long periods of time, weaken the bonds between mineral grains, and that it would be thus possible for disintegration to occur along these boundaries. It’s also been noted that frost is much more effective than heat in producing mechanical weathering.

When water freezes, its volume increases about 9 per cent. So when water expands as it passes from the liquid to the solid state it sets up pressures that are directed outward from the inside of the rock.

THERMOSTATS

Heat causes substances to expand. This is because heat causes the atoms and molecules in the substance to move more quickly. As a consequence, they take up more space. This is true for gases, liquids and solids, but gases expand much more than liquids, and liquids much more than solids. When a substance is cooled, the molecules slow down and as a result the substance contracts.

Thermostats make use of the principle of expansion. The function of a thermostat is to maintain a constant temperature over a period of time. They are used in refrigerators, heating and cooling systems and many industrial processes.

When different materials are heated, some expand more than other. For example, if brass is heated by one degree Celsius, it will expand by one fifty-thousandth of its length. Heating copper, on the other hand, will cause it to expand by about 90% of this. One kind of thermostat contains a strip of brass and a strip of copper which are joined to form a bimetallic strip. When the strip is heated, the different metals expand by different amounts. As a result, the strip is forced to bend towards the side which expands less. This bending can be used to operate a valve or open and close an electrical circuit.

Such a bimetallic strip is used in central heating systems. It switches off the heaters when the air reaches a certain temperature, and switches them on when the temperature falls. One end of the strip can move while the other is fixed The free end completes an electrical circuit which controls the gas or oil burner. The strip bends as it is heated. At a certain temperature the strip bends sufficiently to break the contact, thereby switching off the burner. When the air cools, the strip contracts until it makes contact and switches the burner on again.

SOME FACTS ABOUT OXYGEN

Scientists have been looking for ways to protect the living from the lethal influence of ionizing radiation since the discovery of radioactivity.

More than 30,000 different chemical combinations were tested, but unfortunately none of them were found to be applicable to man due to their high toxicity. It is quite possible to increase the organism’s resistance to radiation in a low-oxygen chamber. But these chambers are known to be very expensive and complicated.

A fairly simple method of protection from ionizing radiation has been developed in the USSR. It requires neither a rarefied air chamber nor a special suit.

Air similar to that found at the mountain altitudes of 3.5-5.5 thousand metres above the sea level is pumped in through a face mask. Its oxygen content is twice as low as that of normal air on the plain. Similar mixtures have been used in various investigations of both ill and healthy people for nearly fifty years. This proportion proved to be the best. The experiments demonstrated that animals survive otherwise lethal doses of radiation after being exposed to such a gas mixture.

Human and animal bodies consist of about 80 per cent water.

Radiation causes it to form compounds which actively enter into reaction with biomolecules of the cells causing their damage. The lower the oxygen content in the tissues, the fewer such combinations, which means less damage from ionizing radiation. In other words, lower oxygen content results in a greater resistance of healthy normal cells to radiation.