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Explain the factors that affect electric resistance.

Answer
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Hint:Electric resistance or resistance is the opposition offered by the conductor for the flow of current. S.IUnit for electric resistance is ohms (Ω). According to ohm’s, the voltage is directly proportional to the electric current at constant temperature. The proportionality constant is known as resistance i.e, R=VI.

Complete answer:
The resistance of a conductor depends upon following factors:
-Length of the conductor: Resistance of a conductor is directly proportional to the length of the conductor that is as the length increases, the resistance of the conductor increase
Rl………….......(1)

-Area of cross section:
Resistance of a conductor is inversely proportional to the area of cross section of the conductor that is as the area of cross section increases, the resistance of the conductor decreases.
R1A ...(2)

-Temperature: Resistance of a conductor is directly proportional to the temperature that is as the temperature increases, the resistance of the conductor increases.
RT ...(3)

-Nature of material: Different materials have different concentrations of free electrons therefore different materials have different resistance. Therefore resistance varies for different materials.
From equation (1) and equation (2), we get
RlA ...(4)
On removing the proportionality above equation can be written as
R=ρlA ...(5)
Where, ρ= constant of proportionality (Resistivity)

Note:Resistivity or specific resistance is the resistance offered by the conductor of unit area of cross section and unit length. S.IUnit for specific resistance is ohm metre(Ωm). The material which obeys ohm’s law is known as ohmic resistors and the materials which don’t obey ohm’s law are known as non ohmic resistance.