Question

A cylindrical rod has length $L$ and resistance $R$. If it is melted and formed into another rod of length $2L$ , the resistance will be :

• A. $R$
• B. $2R$
• C. $4R$
• D. $8R$

Answer 1

The correct option is C $4R$

$R=\frac{\rho \ell }{A}$
$R=\frac{\rho \ell }{A}\times \frac{\ell }{\ell }$
$R=\frac{\rho {\ell }^2}{V}$
$R=\frac{\rho (2\ell {)}^2}{V}=4R$