Question

A coil of annealed copper wire has 820 turns, the average length of which is 9 in. If the diameter of the wire is 32 mils, calculate the total resistance of the coil at 20 degree celsius.

Answer 1

$Resistance=N\space \rho\frac{l}{A}$

$Area\space of \space cross section=\frac{\pi d^{2}}{4}$

Therefore resistance =$4N\rho\frac{l}{\pi d^{2}}$

Resistivity of annealed copper at $20\degree$is $1.72\times10^{-8}$

length =$9\space inches=0.2286m$

$N=820 \space turns$

Diameter=$32\space mils=0.0008128m$

Resistance=$4(820)(1.72\times10^{-8})\frac{0.2286}{\pi \times 0.0008128^{2}}=6.2132$

Resistance= 6.2132 $\Omega$