Q. The resistance of a $5\ cm$ long wire is $10\ \Omega.$ It is uniformly stretched so that its length becomes $20\ cm.$ The resistance of the wire is
A) $160\ \Omega$
B) $80\ \Omega$
C) $40\ \Omega$
D) $20\ \Omega$
Explanation
(a) $\frac{R_{1}}{R_{2}} = \left( \frac{l_{1}}{l_{2}} \right)^{2} \Rightarrow \frac{10}{R_{2}} = \left( \frac{5}{20} \right)^{2} = \frac{1}{16} = R_{2} = 160\Omega$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.