RESISTANCE AND LAW OF RESISTANCE
RESISTANCE
Conductor:
A
material which gives up free electrons easily and offer little opposition
resistance to flow of current is called conductor.
Example: Gold,
Silver, Copper, Aluminum, Iron, Brass
Insulator:
A
material which does not give up free electrons easily and offers great
opposition resistance to flow of current is called insulator.
Example: Glass, Rubber, Oil, Porcelain, Ceramic
Resistance:
(R)
Opposition offered to the flow
of electrons in any substance is called Resistance, it is denoted by Ω and
measured in ohm.
All materials have resistance, which we used as a conductor
in wires and cables. Two materials copper and aluminum are using as a conductor
in wires. Electrician must follow the law of resistance during lying and installation
of a wire or cable.
LAW
OF RESISTANCE
1.
The resistance of a
conductor varies directly as its length.
Example:
one meter of a copper wire has
a resistance of 0.03Ω then 2 meters will have 0.06Ω and 40 meters a resistance
of 1.2Ω.
2.
The resistance of a
conductor varies inversely as its cross section.
Example:
If a piece of wire has twice
the cross-section of another of the same material and length, it will have only
half the resistance.
3.
The resistance of a conductor
depends on the material.
Example:
A piece of wrought iron will
have 8.84 times the resistance of a piece of copper of the same length and
cross-section.
4.
The resistance of a
conductor depends on its temperature.
Page No. 13
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