Question

A wire of length L and resistance R is streched to get the radius of cross-section halved. What is the new resistance of the wire?

• A. 5 R
• B. 8 R
• C. 4 R
• D. 16 R

Answer 1

The correct option is D 16 R

By using $\frac{R_1}{R_2}={\left(\frac{r_2}{r_1}\right)}^4\Rightarrow \frac{R}{R^{{}^{\prime }}}={\left(\frac{\frac{r}{2}}{r}\right)}^4\Rightarrow R^{{}^{\prime }}=16R$