Question

Wire resistance $R$ is stretched to thrice of its original length, what is its new resistance

• A. $9R$
• B. $\frac{R}{9}$
• C. $3R$
• D. $R/3$

Answer 1

The correct option is A $9R$

As volume is constant is streching of wire
$A_1{l}_1=A_2{l}_2$
$R=\rho \frac{l}{A}$
$l_2=3l_1$
$A_2=\frac{A_1}{3}$
$\Rightarrow R^{\prime }=\frac{\rho \times 3l}{\frac{A}{3}}$
$R^{\prime }=9R$