Question

A copper wire has diameter 0.5mm and resistivity 1.6x10^-8ohm m what will be the length of this wire to make its resistance 12 ohm

Answer 1

Here is your answer

Resistance = rho × length÷area of cross section.

Resistance R = 12 ohm
Resistivity (rho)= 1.6×10^(-8)ohm.m
Radius = diameter÷2 = .5/2 = .25mm. = [0. 25×10^(-3)]m
area of cross section= π.r.r

= π×[.25×10^(-3)]×[(. 25)×10^(-3)]

put these in equation
then we have

12=[1.6×10^(-8)×length]÷[π×0.0625×10^(-6)]

rearranging terms ,
12×π×0.0625×10^(-6) =1.6×10^(-8)×length
so
length = [12×π×0.0625×10^(2)] ÷ [1.6]

= 1.472m

Hope it helped you.