The resistance of a metal wire of length 1 m is 25 Ω at 20° C. If the diameter of the wire is 0.3 mm, What must be the resistivity of metal at that temperature?
We have,
Length of the metal wire, l = 1 m
Diameter of the wire, d = 0.3 mm
Radius, r = 0.3/2 mm = 0.15 mm
= 0.15 x 10-3 m
Resistance of the metal, R = 25 Ω
Thus,
Resistivity (ρ) = 
⇒ ρ = 
⇒ ρ = 
⇒ ρ = 1.9625 × 10-6 Ωm
The resistivity of the metal is 1.9625 × 10-6 Ωm
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