Insulator
Insulators are the materials from
which electrons cannot move freely and provides large amount of resistance that
electric current cannot pass from it and these are used to protect from
electricity. Electrons and ions in insulators are bound in the structure and
cannot move easily as much as 1023 times more slowly than in
conductors. Pure water and dry table salt are insulators, for example, whereas
molten salt and salty water are conductors. Examples of insulators are glass,
porcelain, rubber, paper, polyethylene, fiberglass etc.
Examples of Insulators are:
Rubber, Glass, Pure water, Oil,
Air, Diamond, Dry wood, Dry cotton, Plastic, Asphalt, Fiberglass, Dry paper,
Porcelain, Ceramics, Quartz, Yarn, Fabric, cotton.
Energy Bands in Insulator
The concept of the Energy bands
is very useful for us to understand the various properties of solids. We can
determine from the nature of the energy bands that the material is an
electrical, insulator or a semiconductor.
In an insulator at zero
temperature, the highest band that is filled completely called the valence band
and it is also the highest band that has electrons in it. The next higher band
is the conduction band and it is completely empty and there are no electrons in
it.
Consider the two outermost energy
bands of a material in which the lower band is filled with electrons and the
higher band is empty. The lower filled band is called the valence band and the
upper empty band is the conduction band. The conduction band is the one that is
partially filled in a metal. It is common to refer to the energy separation
between the valence and conduction bands as the energy gap of the material. The
Fermi energy lies somewhere in the energy gap. Suppose a material has a
relatively large energy gap of approximately 5 eV. At 300 K (room temperature)
the Fermi–Dirac distribution predicts that very few electrons are thermally
excited into the conduction band. There are no available states that lie close
in energy above the valence band and into which electrons can move upward to
account for the extra kinetic energy associated with motion through the
material in response to an electric field. Consequently, the electrons do not
move, the material is an insulator. Although an insulator has many vacant states
in its conduction band that can accept electrons, these states are separated
from the filled states by a large energy gap. Only a few electrons occupy these
states, so the overall electrical conductivity of insulators is very small.
Insulation of Electrical Wires
Some insulators are used on electrical
conductors and wrapped on it to separate with other wires to provide insulated
conductors and use them as electrical wires. These insulating materials are
polyvinyl chloride, PVC (Polyvinyl Chloride), PE (Polyethylene),
ECTFE, PVDF, Nylon etc.
Power Transmission Insulators
The purpose of an insulator in an
electrical transmission and distribution system is to prevent the flow of electric
current between any electrically charged part of the system or another charged
or non-charged metal part. In other words, insulators are used to prevent from
flow of electric charge between two parts of the system and to provide
insulation between them. It also supports the overhead line conductor and supports
the weight of the conductor. Most of the insulators are made of materials of
porcelain, glass, stealite, polymer etc.
Source: -
-
College Physics | Openstax College
-
Physics for Scientists and
Engineers with Modern Physics 9th
Edition | Serway - Jewett
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