Английский язык. Громовая И.И - 81 стр.

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79
constant voltage, that is, the voltage neither rises nor falls. A pulsating direct
current is that kind of electric current that flows in the same direction through
a circuit but varies in its voltage value.
An alternating current is an electric current, alternating or varying both in
amount and direction, its abbreviation is A. C. The alternation may occur
(take place) from a few per second up to several million per second. Two
alternations make a cycle. The number of cycles in one second is called the
frequency of an alternating current.
An oscillating current is similar to A. C. in shape but has a constant frequency
and its amplitude is damped. Transient currents usually damp away extremely
rapidly. One should mention unidirectional transient and A. C. transient types
of electric current.
(1800 t. un.)
NOTES:
1
according to – согласно, в соответствии с
2
in addition to – кроме
Text 2. Sources of Electrical Energy
To produce an electric current requires employing a chemical, as in the
battery, or a mechanical, as in the electromagnetic generator, source of energy.
Energy is not created by an electric energy source, but is only converted
into an electrical form from another one, such as mechanical, chemical, thermal
or radiant energy. In waterpower plants, the energy of falling water is converted
into electrical or into heat when coal is burnt. Chemical sources of current
have limited application as great quantities of electric energy generated today
come from various forms of mechanical energy.
For the first time mechanical energy was converted into electrical one by
means of electrostatic machines. As industrial application of energy increases
greater amount of energy is needed every year. The energy needs will continue
to grow while the energy sources of the world are decreasing.
Coal oil and gas have been man’s main sources of heat from ancient times
and today they are our basic sources of energy. However, coal and other kinds
of fuel are often replaced by atomic energy. Man has learned to split atoms
with the help of a nuclear reactor in order to get great quantities of energy. For
example, a ton of uranium can give us as much energy as about 3 million tons
of coal.
The Earth contains inside it a practically inexhaustible supply of thermal
energy, which can be used for economic needs.

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