More examples

Example $4$:

A wire that has a diameter of $0\mathrm{.}085$ inches. How much its circular mils?

$1$mil$=\frac{1}{1000}$ inch

$0\mathrm{.}085$ inches $=\frac{85}{1000}$

$\frac{85}{1000}$ inches $=85$mils

Circular mils $={85}^2=7225$

Example $5$:

If a current of $20$ amps flows through $90$ feet Copper wires that has a diameter of $0\mathrm{.}085$ inches. How much voltage the wire will drop?

The equations that we use is

Resistance $($R$)=\frac{KxL}{CM}$

Voltage Drop $($V$)=$ I x R

$(K)$ for copper is $=10\mathrm{.}4$

$($L$)$ wire length $=902=180$ feet

$($CM$)$ circular mils $={85}^2=7225$

$($I$)$ current $=20$ Amps

Then

$R=\frac{10\mathrm{.}4180}{7225}=0\mathrm{.}259$ ohms

$V=IR=200\mathrm{.}259=5\mathrm{.}18$ volts