CONDUCTIVITY OF METALS
INTRODUCTION:
The most important properties of metals are their high thermal and electrical conductivities.
Silver has the highest electrical conductivity. Copper comes next and is similar to silver from the
point of view of atomic structure ; both belonging to the same group of periodic table. The
conductivity of copper is less than that of silver. Since supplies of copper are not abundant in
nature, aluminium which is light and has a high conductivity is rapidly becoming more important
as a conductor material. Gold which has a conductivity higher than that of aluminium but lower
than that of silver or copper does not find use in electrical industry because it is expensive.
Metals having complex structures such as As, Sb, Bi, Sn, Hg have lower conductivities which lie
between those of ideal metal (very high conductivity) and of insulators (negligible
conductivities).
FACTORS AFFECTING THE RESISTIVITY OF ELECTRICAL MATERIALS
1. Temperature : The electrical resistance of most metals increases with increase of
temperature while those of semiconductors and electrolytes decreases with increase of
temperature. Many metals have vanishing resistivity at absolute zero of temperature
which is known as superconductivity.
2. Alloying : A solid solution has a less regular structure than a pure metal. Consequently,
the electrical conductivity of a solid solution alloy drops off rapidly with increased alloy
content. The addition of small amount of impurities leads to considerable increase in
resistivity.
3. Cold Work : Mechanical distortion of the crystal structure decrease the conductivity of a
metal because the localized strains interfere with electron movement.
4. Age Hardening : It increases the resistivity of an alloy.
MOTION OF AN ELECTRON IN AN ELECTRIC FIELD
In a conductor, the electrons are moving about with random velocity , the magnitude of which
depends upon the temperature. There are two comonents of motion, as follows :
1. Random motion , due to thermal effects.
2. Directed motion , the direction being determined by the polarity of the electric field.
EQUATION OF MOTION OF AN ELECTRON
When no electric force is applied , the free electrons move about through the conductor in a
random manner in such a way that the number of electrons moving from right to left is the same
as the number moving from left to right and the resultant current is nil. If an electric force is
applied to the conductor, each electron has superposed on to its random motion, a motion
impressed on it by electric force, and the electrons as a whole are driven through the conductor
by the continued action of this electric force.
INTRODUCTION:
The most important properties of metals are their high thermal and electrical conductivities.
Silver has the highest electrical conductivity. Copper comes next and is similar to silver from the
point of view of atomic structure ; both belonging to the same group of periodic table. The
conductivity of copper is less than that of silver. Since supplies of copper are not abundant in
nature, aluminium which is light and has a high conductivity is rapidly becoming more important
as a conductor material. Gold which has a conductivity higher than that of aluminium but lower
than that of silver or copper does not find use in electrical industry because it is expensive.
Metals having complex structures such as As, Sb, Bi, Sn, Hg have lower conductivities which lie
between those of ideal metal (very high conductivity) and of insulators (negligible
conductivities).
FACTORS AFFECTING THE RESISTIVITY OF ELECTRICAL MATERIALS
1. Temperature : The electrical resistance of most metals increases with increase of
temperature while those of semiconductors and electrolytes decreases with increase of
temperature. Many metals have vanishing resistivity at absolute zero of temperature
which is known as superconductivity.
2. Alloying : A solid solution has a less regular structure than a pure metal. Consequently,
the electrical conductivity of a solid solution alloy drops off rapidly with increased alloy
content. The addition of small amount of impurities leads to considerable increase in
resistivity.
3. Cold Work : Mechanical distortion of the crystal structure decrease the conductivity of a
metal because the localized strains interfere with electron movement.
4. Age Hardening : It increases the resistivity of an alloy.
MOTION OF AN ELECTRON IN AN ELECTRIC FIELD
In a conductor, the electrons are moving about with random velocity , the magnitude of which
depends upon the temperature. There are two comonents of motion, as follows :
1. Random motion , due to thermal effects.
2. Directed motion , the direction being determined by the polarity of the electric field.
EQUATION OF MOTION OF AN ELECTRON
When no electric force is applied , the free electrons move about through the conductor in a
random manner in such a way that the number of electrons moving from right to left is the same
as the number moving from left to right and the resultant current is nil. If an electric force is
applied to the conductor, each electron has superposed on to its random motion, a motion
impressed on it by electric force, and the electrons as a whole are driven through the conductor
by the continued action of this electric force.
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