Question

Resistance of a wire is 20 ohm, it is stretched upto three times of length, then its new resistance will be

• A. $6.67\Omega$
• B. $60\Omega$
• C. $120\Omega$
• D. $180\Omega$

Answer 1

The correct option is D $180\Omega$

$\frac{R_1}{R_2}=\frac{{\ell }_1}{A_1}\times \frac{A_2}{\ell }=\frac{{\ell }_1^2}{V}\times \frac{V}{{\ell }_2^2}\Rightarrow \frac{R_1}{R_2}=\frac{{\ell }_1^2}{{\ell }_2^2}{R}_2=9\times 20=180\Omega$