Factors on which Resistance depends
Resistance of a conductor depends:
- On its length
- On its area of cross-section
- On the nature of its material
- Resistance of uniform metallic conductor is directly proportional to its length and inversely proportional to area of cross-section.
Therefore, R = ρ(l / A),ρ(rho) is constant of proportionality.
- ρ is called electrical resistivity of the material of the conductor. SI unit is Ωm.
- Resistivity of conductors is very low whereas the insulators have a very high resistivity.
- Resistivity varies with Temperature.
- Alloys having higher resistivity than metals are used in electrical heating devices, like iron and toasters, tungsten is used in filament of electric bulbs and copper and aluminium are used for electrical transmission lines.
Resistivity of Conductors < Resistivity of Alloys < Resistivity of Insulators