The resistance of a copper wire 200m long is 21Ω. If its thickness (diameter) is 0.44 mm, its specific resistance is around -

Correct option is A

To calculate the specific resistance (resistivity) of the copper wire, we can use the formula:

Where:
· R is the resistance (21 Ω)
· L is the length of the wire (200 m)
· A is the cross-sectional area of the wire
The cross-sectional area AAA for a wire with a circular cross-section is given by:


Given:
· Diameter d=0.44 mm=0.44×10−3 m
· L=200 m
· R=21 Ω
First, calculate the area A:

Now, calculate the resistivity ρ:

The correct answer is (a) 1.6 × 10^-8 Ω-m.