UNIT 14
Grammar: Complex Subject
TEXT 14 A
Superconductivity
Low temperature physics is know to be making rapid progress. Greatexperemental and theoretical programmes are under way in this branch oh physics. Scientists all over the world take part in international conferences of physicists. Where they discus problems of crating new superconductors with high resolving properties. The low temperature physics deals with various phenomena occurring at temperatures in the region of absolute zero (-273ºC). The lowest temperature on Earth is known to have been registered in the Antarctic about -80ºC. Still lower temperatures are claimed to be found on other planets. On Saturn, for instance, it reaches –153, on Uranus –173, on Neptune –193. On Pluto – the planet most remote from the sun- the temperatures appears to be below –218C. Even this, however, is believed not to be the limit. A temperature of –273ºC has been found to be possible in nature. In laboratory experiments scientists have achieved a temperature, which differs from absolute zero by 1/10,000 of a degree.
Having learnt to control heat, man has multiplied its potential many times over, learned to cut and melt metal and found many other useful applications for it. Cold is considered to be quite useful.
The study of different substances at low temperatures has revealed many interesting phenomena. One of the most amazing (surprising) was superconductivity –the complete loss of resistance to electrical current. This property has been found in more than 20 metals. If an electric current is sent through a ring of cooled metal of this type, it will circulate for a very long time.
Superconductivity has long been the subject of pure theory and it seemed that it would never be possible to apply it in practice. However, instruments have been developed using this phenomenon.
Of particular interest are the superconductive alloys widely applied in the development of superconductive magnets, which make possible, with a small expenditure of power, to obtain permanent magnetic fields of scores and hundreds of thousands of oersteds1 .
Of great interest are recent theoretical studies that indicate the possibility of developing superconductors retaining their properties at room and even higher temperatures. Their practical application could open up a new chapter in the use of electric power. It could multiply the efficiency of electrical machines and save billions of kilowatt hours in transmitting power over long distances.
TEXT 14 B
Liquid helium surprises
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1. All solid bodies become brittle while liquids and gases become solid at temperatures close to absolute zero. There is only one gas – helium which fails to solidify on cooling alone. Solid helium is obtained by cooling and simultaneously subjecting it to high pressure.
2. At temperatures near to absolute zero, liquid helium reveals a surprising property – super fluidity. This phenomenon, discovered by Pyotr Kapitza, defies all conventional concepts of physics. For instance, if liquid helium is poured into a vessel it immediately climbs up the internal walls of the vessel and overflows. On the contrary, if an empty cup is partially submerged in liquid helium, the latter quickly fills it to the level of the surrounding liquid.
3. The range of investigations into low temperature has grown and is certain to grow with the progress of physics. Low temperatures are now used in certain studies in nuclear physics, radio-physics, electronics, optics, chemistry and biology. Particularly wide application, however, has been found for them in diverse research into the physics of solids.
Cryogenic propellants
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At ordinary temperatures hydrogen and oxygen, and some other potential propellants, for example fluorine, are gases and not until they are in a gaseous state do they undergo chemical reaction in the rocket engine. But in the gaseous form they have such low densities that it would require extremely large tanks to store them in the rocket vehicle. The storage of propellants in the gaseous form is thus completely impractical. It is for this reason that the substances mentioned above are stored as liquids at very low temperatures; they are consequently referred to as “cryogenic propellants” (from “Kryos” – “ice cold” in Greek).
In the liquid form, the densities are much greater than in the gaseous state, and consequently the propellant tanks can be much smaller and less massive. This advantage is offset, however, by the low temperature required, so that liquid hydrogen, liquid fluorine, and liquid oxygen cannot be stored in the rocket tanks for long periods of time, nor can they be used without special precautions.
Such nonstorable, cryogenic propellants must be loaded into the tanks shortly before the rocket is launched.
Simultaneously compressing and cooling the gases to the required low temperature make the cryogenic liquids. They are then stored and transported, with moderate loss, in special vacuum-jacketed tanks. These containers are designed on the same principle as the familiar vacuum- bottles used to store hot or cold liquids in the home.
Here you can see the temperatures at which a number of cryogenic liquids, of possible use as propellants, liquefy at ordinary atmospheric pressure. These temperatures represent the conventional boiling points of the various liquids. By increasing the pressure in the container the boiling points can be raised to a certain extent, so that the liquid form can exist at somewhat higher temperatures. It can be seen, however, that the temperatures required to produce and store cryogenic propellants are extremely low by normal standards.