Question

The electric resistance of a certain wire of iron is R. If its length and radius are both doubled, then?

• A. The resistance will be halved and the specific resistance will be doubled
• B. The resistance and the specific resistance, will both remain unchanged
• C. The resistance will be doubled and the specific resistance will be halved
• D. The resistance will be halved and the specific resistance will remain unchanged

Answer 1

The correct option is B The resistance and the specific resistance, will both remain unchanged

$R\propto \frac{l}{r^2}\rho \frac{R_2}{R_1}=\frac{l_2}{l_1}\ast \frac{{r_1}^2}{{r_2}^2}=\left(21\right)\ast \left(12\right)2=12ÞR_2=R_1,$specific resistance doesn't depend upon length,and radius.