The following are the main laws of resistance:
(i) Resistance of a conductor is directly proportional to its length, provided temperature and other physical conditions remain unchanged.
It means that R ∝ l i.e., if the length increases, the resistance also increases and if length decreases, its resistance also decreases.
(ii) Resistance of a conductor is inversely proportional to its area of cross section, other conditions remaining the same.
(iii) R depends on the nature of the material of the conductor. It means, if we take equal lengths of wires of copper, aluminium and iron and all of the same cross-sectional area, their resistance are different from each other since they are of different materials.
