Question

Explain the factors that affect electric resistance.

Answer 1

Hint:Electric resistance or resistance is the opposition offered by the conductor for the flow of current. $S.I$Unit for electric resistance is ohms $\left( \Omega \right)$. 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, $R = \dfrac{V}{I}$.

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
$R \propto l$………….......$\left( 1 \right)$

-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.
$R \propto \dfrac{1}{A}$ $...(2)$

-Temperature: Resistance of a conductor is directly proportional to the temperature that is as the temperature increases, the resistance of the conductor increases.
$R \propto T$ $...\left( 3 \right)$

-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 $\left( 1 \right)$ and equation $\left( 2 \right)$, we get
$R \propto \dfrac{l}{A}$ $...\left( 4 \right)$
On removing the proportionality above equation can be written as
$R = \dfrac{{\rho l}}{A}$ $...(5)$
Where, $\rho = $ 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. $S.I$Unit for specific resistance is ohm metre$\left( {\Omega m} \right)$. 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.