Question

The length and area of cross -section of a conductor are doubled, then its resistance is

• A. halved
• B. unchanged
• C. doubled
• D. quadrupled

Answer 1

The correct option is B unchanged

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

$l^{\prime }=2l$ and $A^{\prime }=2A$

Hence, $R^{\prime }=\rho \frac{l^{\prime }}{A^{\prime }}$

$⟹R^{\prime }=\rho \frac{l^{\prime }}{A^{\prime }}=\rho \frac{2l}{2A}=\rho \frac{l}{A}$

$⟹R^{\prime }=R$

Hence, resistance remains unchanged.

Answer-(B)