Resistance of a metal wire of length 2 m is 20 Ω at 20°C. If the diameter of the wire is 0.3 mm, what will be the resistivity of the metal at that temperature?

Resistance R of the wire = 20 Ω, the diameter
d = 0.3 mm = 3 × 10-4 m, and the length l of the wire = 2 m. Therefore, the resistivity of the given metallic wire is ρ = (RA/l) =(Rπd2/4l)
Substitution of values in this gives
ρ = 1.84 × 10–6 Ω m