Сборник технических текстов для домашнего чтения по английскому языку. Морозова М.А. - 7 стр.

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The disadvantage of power plants utilizing nuclear fuel is their radiation. Ra-
dioactive radiation produced in the reactors is dangerous for attending personnel.
Therefore, the reactors and steam generators are installed underground. They are also
shielded by thick (up to 1.5 m) concrete walls. All their controls are operated by
means of automatic devices. These measures serve to protect people from radioactive
radiation.
Types of Current
Current is a flow of electricity through a circuit. Let us consider two riain types
of current: direct and alternating. A direct current (d.c.) flows through a conducting
circuitin one direction only. It flow spro-vided a direct voltage source is applied to
the circuit.
An alternating current (a.c.) is a current that changes its direction of flow
through a circuit. It flows provided an alternating voltage source is applied to the cir-
cuit. Alternating current flows in cycles. The number of cycles per second is called
the frequency of the current. In a 60-cycle alternating current circuit the current flows
in one direction 60 times and in the other direction 60 times per second.
It is easy to transform a.c. power from one voltage to another by a transformer.
Transformers are also used to step down the voltage at the receiving point of the line
to the low values that are necessary for use.
When necessary a.c. can be changed into d.c. but this is seldom necessary.
Among the most common meters used there are the ohmmeter, the ammeter
and the voltmeter. The ohmmeter is used to measure the value of resistance. It con-
sists of a milliammeter calibrated to read in ohms, a battery and resistors. The meter
is connected in parallel and the circuit is not opened when its resistance is measured.
The readings on the scale show the measured value.
The ammeter is used to measure the value of current. When the ammeter is
used the circuit should be opened at one point and the terminals of the meter should
be connected to it. One should take into consideration (hat the positive terminal of
(lie meter is connected to (he positive terminal of (he source; the negative terminal -
to the negative terminal of the source. The ammeter should be connected in series.
The readings on the scale show the measured value.
Capacitors
A capacitor is one of the main elements of a circuit. It is used to store electric
energy. A capacitor stores electric energy provided that a voltage source is applied to
it. The main parts of a capacitor are metal plates and insulators. The function of insu-
lators is to isolate the metal plates and in this way to prevent a short.
In the diagram one can see two common types of capacitors in use nowadays: a
fixed capacitor and a variable one. Тhe plates of a fixed capacitor cannot be moved;
for his reason its capacity does not change. The plates of a variable capacitor move;
its capacity changes. The greater the distance between the plates, the less is the ca-
pacity of a capacitor. Variable capacitors are commonly used by radiomen; their
function is to vary the frequency in the circuit. Fixed capacitors are used in telephone
and radio work.
Fixed capacitors have insulators produced of paper, ceramics and other materi-
als; variable capacitors have air insulators. Paper capacitors are commonly used in

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