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on the activities of electrons inside
an atom.
Atomic Theory
Electrons are negatively charged
particles spinning rapidly round a
nucleus of positive- and neutrally
charged ones, called protons and
neutrons, respectively, as shown below
(the neutrons keep the protons
together, since particles of a like
charge are repelled):
None of them are physical in nature,
but are actually electromagnetic
charges, or tiny whirlwinds of
electromagnetic force. A collection
of atoms is called a molecule, which is
the smallest part of any object that
retains the identity of it.
Put very simply, if you line up a
series of atoms (as in an electrical
cable) and add an electron to the
first one, it will repel those already
there until one is pushed out, which
joins the next atom, and so on down
the line until an electron falls off the
last one, giving you an electric
current. When the electron is pushed
in at first, there is a difference in
potential between that end of the
cable and the other end, creating a
potential difference (another name for
voltage). In other words, the flow of
electricity is like that of wind moving
from high to low pressure.
Some atoms don’t have much of a
hold on their electrons, and allow
them to move easily – the materials
made up of these are called conductors
114 JAR Private Pilot Studies
(copper is a good example – gold is
only used because it doesn’t tarnish
in a hurry, and cause bad
connections. A gas can also conduct
electricity). Those that keep a tight
hold and therefore allow no
movement are found in insulators,
which are used to keep conductors
from touching each other, otherwise
electricity would flow where you
don’t want it – if electricity takes a
short cut (known as a short circuit) it
generates massive amounts of heat,
with the obvious consequences.
Good examples of insulators would
be glass, or the plastic coating round
a cable.
Somewhere between a conductor
and an insulator is a semiconductor
which is created by adding a certain
amount of impurity to a material
normally considered to be an
insulator. Electricity will then flow
only under certain circumstances,
such as the influence of an
electromagnetic field, or the polarity
of the source of a current (this is the
basis of the transistor).
There must be an equal number of
electrons to protons, which is why
an extra electron (or a hole caused
by one leaving), is balanced
immediately. An atom with one extra
is negatively charged, and with one
missing is positively charged. This
process is called ionisation, because an
atom wrongly charged is called an
ion, which we will come across latter
when we look at the ionosphere, or
what is now called the mesosphere.
Some components, like transistors,
depend on the movement of
electrons or holes (missing electrons)
one way or the other.
Electrons spinning round an atom
occupy energy levels, or shells, rather
like the orbits of the planets around
the Sun. The first shell can hold up
to 2 electrons, and the second up to
8, but it’s always the outer shell,
which contains valence electrons that is
important. Such atoms can be
dislodged easily by applying stress in
the form of heat or a magnetic field,
which is how an electrical current is
produced.
Electricity
There are three types of electricity:
· That which stays right where it
is, called static electricity.
· That which goes in one
direction only, usually at one
speed, called Direct Current.
· That which flip-flops back and
forth to form a wave pattern, or
Alternating Current.
The essential point is movement, since
nothing much happens when
everything is still, but it is the last
one, AC, with which we will mainly
be concerned.
Batteries
Certain chemicals when combined
with metals can cause electrons to
flow as direct current, until all the
electrons disappear from the metal,
causing it to eventually get eaten
away – since the atoms comprising it
lose electrons, they cease to be the
same atoms and therefore cease to
exist in their former state – if you
could contrive to put the electrons
Electricity & Radio 115
back, you would regain your metal
plate, and recharge the battery.
Actually, a battery is a collection of
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