Given,
diameter of copper wire = 0.5mm = 5 × 10-⁴m
restivity = 1.6 × 10 ^-8 ohm.m
resinstance = 10 ohm
length =?
we know,
R = dL/A
where A , d , L and A are resistance , restivity , length and cross section area.
10 = 1.6 × 10^-8 × L/(πr²)
L = 10 × 3.14 × (2.5 × 10^-4)² × 10 ^-8/1.6
L = 10 × 3.14 × 6.25/1.6
L = 122.656 m
