Radiophysics. Халюшева Г.Р. - 37 стр.

structure. It also provides a mental picture that permits visualizing many electrical phenomena and how electronic devices
operate.
         Physicists do not agree on the exact structure of atoms and many phenomena associated with them, particularly
within the nucleus. But the simple solar–system conception we have discussed serves our purpose completely.
         Electron Flow. Not so long ago textbooks told us that the precise nature of electricity was not known, that it was
an invisible and mysterious agent manifesting itself in many ways. Today we know this invisible and mysterious agent to be
a flow of particles called "electrons", which form part of all atoms.
         Flow of an electric current is now accepted as being a slow drift of so–called "free electrons" through a conductor.
How these free electrons are made available has not yet been definitely established. One of the most rational conceptions
maintains that electrons in the outer orbits of the atoms of a conductor may at times be subjected to equal influences of two
or more atoms.
         Until quite recently it was believed that an electric current flowed through a conductor at the speed of light,
186,000 miles per second. Now we know that the electron flow, which is the so–called "electric current", is slow under
normal conditions, but an electrical impulse is transmitted through the circuit at the speed of light.
         When a voltage is applied to the ends of a circuit, it creates a field of force inside the conductor. This field gives
direction to the random movement of the free electrons and causes what appears to be their coordinated, slow, average drift
from one atom to another. The higher the voltage applied to a given circuit, the faster the electrons drift along the conductor,
consequently the greater the current.
         But under normal full load on a light or power circuit, the electron drift is only about 1 foot per hour. Consequently
it may require days for the electrons in a long d–c circuit to drift from one end to the other. In an a–c circuit when the
voltage reverse 50 or 120 times per second, the electrons cannot drift far in either direction but swing back and forth
through short distances in the circuit.

         9.2 Words and word–combinations to be remembered
         Available – доступный; имеющийся в распоряжении
         to govern – управлять
         matter – вещество; материя
         to be composed of – состоять из
         hydrogen – водород
         oxygen – кислород
         nitrogen – азот
         carbon – углерод
         lead – свинец
         iron – железо
         silver – серебро
         gold – золото
         substance – вещество; материя
         to separate – отделять; разлагать (на части)
         scale – зд. система
         artificially – искуственно
         particle – частица
         negative (positive) charge – отрицательный (положительный) заряд
         to weigh – весить
         neutral – нейтральный
         nucleus (pl.–nuclei) – ядро
         to rotate – вращать(ся)
         solar system – солнечная система
         to revolve – вращать(ся), вертеть(ся)
         inch – дюйм (=2,5 см)
         to enlarge – увеличивать
         ordinary – обычный; ординарный
         velocity – скорость
         to tend – иметь тенденцию (к чему–либо)
         to fall together – соединяться
         dense – плотный
         bind (bound; bound) – связывать
         flow – поток
         conductor – проводник