Law of Resistance:
This law states that the resistance of conductor material is directly proportional to the length of the conductor, inversely proportional to the cross-section of the conductor, and depends upon the nature of the conductor material at a constant temperature.
Now, we can say that
R=ρ.(l/a)
Where R= resistance of the conductor material
l= length of the conductor material
a= cross-sectional area of the conductor material
ρ=specific resistance or resistivity of the conductor material.
Factors on which the resistance of a conductor depends:
The following are the factor on which the resistance of a conductor depends:
1. Length of the Substance (L): The resistance of a conductor directly increases with the length of the substance (R ∝ L)
2. The cross-sectional area of substance (A): The resistance of the conductor is inversely proportional to the cross-sectional area of the substance (R ∝ 1/A). If the cross-sectional area increases, the resistance will be decreased.
3. The material used in the substance: The resistance of the conductor varies with the material used (R ∝ ρ)
4. Working Temperature: Resistance of the conductor increases with the rise of temperature but in the case of Insulators, semi-conductors & electrolytes decrease the resistance with the rise of temperature.
5. Nature of Current use: Due to the skin effect, the resistance of the material will be higher when alternating current flows than that of the flow of direct current.
6. Other factors: In some specified materials, the resistance will depend upon magnetic fields, light, pressure, and whatnot. Bismuth shows higher resistance when placed in a magnetic field when the semi-conductor is kept in light energy, its resistance will be lower.