Question

A copper wire has diameter 0.5 mm and resistivity 1.6 x 10-8 ohm meter. what will be the
length of this wire to make its resistance 10 ohm ? How much does the resistance change
if the diameter is doubled?​​

Answer 1

Given:

d=0.5mm=0.5×10^−3 m

r=  d/2 =0.5×10  −3/2 = 0.25×10 ^−3 m

 A=Πr^ 2

=3.14×(0.25×10 −3)^2

 

ρ=1.6×10 ^-8 Ωm

R=10Ω

We know R=Pl/a   

or l=Ra/p  =  1.6×10 ^−8

 10×3.14×(0.25)^2×10^-6

=122.6m