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1.
The electrons move toward the high-potential (more positive) point,
while the ions move toward the low-potential (more negative) point.
2.
However, if a voltage is applied to the two ends of a copper bar by
means of a battery, the free electrons tend to drift toward one end.
3.
Such substances are called semiconductors.
4.
In liquids and gases, however, a two directional flow is made
possible by the process of ionization.
5.
This separation is called electrolysis.
6.
This phenomenon is widely applied in modern technology.
7.
As in gases, the electric current is composed of these flows of
opposite charges.
8.
Insulators cannot conduct electric currents because all their electrons
are tightly bound to their atoms.
9.
However, some are free to move from atom to atom, enabling current
to flow.
ELECTRIC CURRENT CONDUCTION
All electric currents consist of charges in motion. However, electric
current is conducted differently in solids, gases, and liquids. When an electric
current flows in a solid conductor, the flow is in one direction only, because the
current is carried entirely by electrons.
(A)
_________________
Conduction in Solids
The conduction of electric currents in solid substances is made possible
by the presence of
free electrons
(electrons that are free to move about). Most
of the electrons in a bar of copper, for example, are tightly bound to individual
copper atoms.
(B)
________________ Ordinarily the motion of the free
electrons is random; that is, as many of them are moving in one direction as in
another.
(C)
______________________ This end is said to be at a higher
potential and is called the positive end. The other end is said to be at a lower
potential and is called the negative end. The function of a battery or other
source of electric current is to maintain potential difference. A battery does this
by supplying electrons to the negative end of the bar to replace those that drift
to the positive end and also by absorbing electrons at the positive end.
(D)
____________________ A perfect insulator would allow no charge to be
forced through it, but no such substance is known at room temperature. The
best insulators offer high but not infinite resistance at room temperature.
Some substances that ordinarily have no free electrons, such as silicon
and germanium, can conduct electric currents when small amounts of certain
impurities are added to them.
(E)
_____________________ Semiconductors
generally have a higher resistance to the flow of current than does a conductor,
such as copper, but a lower resistance than an insulator, such as glass.
