Question

A wire of diameter d, length l and resistivity ρ forms a circular loop. A current enters
and leaves the loop at points P and Q as shown in the Figure. Show that the resistance R of
the wire is given by the expression (4)
R =
4ρx(l − x)
πd2l

Answer 1

$R=\frac{\rho l}{s}$

$l$ is a length of wire, $S$ is the area of the cut of the wire (circle).

$S=\pi r^2=\pi \frac{d^2}{4}$

So, the resistance is

$R=\frac{4\rho l}{\pi d^2}$