Question

Find the radius of the wire of length 25m needed to prepare a coil of resistance 25Ω. (Resistivity of material of wire is 3.142 x 10^-7Ωm)

Answer 1

Given: l = 25m, R = 25Ω, p = 3.142 x 10^-7Ωm

R `=(pl)/A = (pl)/(pir^2)`

`r^2=(pl)/(piR)=(3.142xx10^-7xx25)/(3.142xx25)`

`r^2 = 10^-7=10xx10^-8`

`r = sqrt(10xx10^-8)`

`r=3.162xx10^-4 m`