Question

A copper wire of resistance 4$\Omega$ is stretched to thrice its original length. The resistance of stretched wirebecomes x times . Find the value of x.

Answer 1

Resistance of a wire is $R=\frac{\rho l}{A}=\frac{\rho l^2}{V}$
here volume V is constant. so $R\propto l^2$
thus, $\frac{R_2}{R_1}=\frac{(3l{)}^2}{l^2}=9$
$\therefore R_2=9R_1$ so $x=9$