Question

A cylindrical wire is compressed in length by $10$. The percentage decrease in the resistance will be

• A. $16\%$
• B. $19\%$
• C. $20\%$
• D. $25\%$

Answer 1

The correct option is B $19\%$

$l\to \frac{l90}{100}$

$R=e\times \frac{L}{A}$

$L^{\prime }=0.9l$

$A^{\prime }=1.1A$

$R^{\prime }=P^{\ast }\frac{0.9L}{1.1A}=0.81R$

change is resistance is $=1-0.8$

$=0.19$

$=19\%$.