What is the resistivity (in ohms-m) of a 2 ohm cylindrical wire when the length and the diameter of the wire are 10 m and 0.4 m respectively?

• A. 0.25
• B. 0.0025
• C. 0.05
• D. 0.025

Answer: (D)

The resistance of the conductor is determined by the 
R = ρL/A
Where
ρ = Resistivity of the conductor
L = Length of the conductor = 10 m
A = Area of the conductor = πR2 = 3.14 × 0.22 = 0.125 m2
R = Resistance = 2 Ω
Therefore the resistivity is
ρ = A × R ⁄ L
= 0.125 × 2 ⁄ 10
ρ = 0.025 Ω-m