Question

A copper wire of resistivity 1.63 x 10^-8 ohm meter has cross section area of 10.3 x 10^4 cm^2 . Calculate the length of the wire required to make a 20ohm coil

Answer 1

ρ = 1.63 X 10⁻⁸ Ohm-m
A = 10.3 * 10⁴ cm²  = 10.3 m²
R = 20 Ohm  

R = ρ L / A

L = R A / ρ = 20 * 10.3 / (1.63 * 10⁻⁸)     m
   =  1.264 * 10¹⁰ m
very long wire indeed...  cross section is very large...that is why the resistance is too small.

If the area A = 10.3 * 10⁻⁴ cm²  = 10.3 * 10⁻⁸ m²
then  L = 20 * 10.3 * 10⁻⁸ / 1.63 * 10⁻⁸   m
               = 126.4 m

Answer 2

Explanation:

Hope it's helpful to you