Q. The resistance of a wire is $20\ ohm.$ It is so stretched that the length becomes three times, then the new resistance of the wire will be
A) $6.67\ ohm$
B) $60.0\ ohm$
C) $120\ ohm$
D) $180.0\ ohm$
Explanation
(d) In case of stretching of wire $R \propto l^{2}$
$\Rightarrow$ If length becomes 3 times so Resistance becomes 9 times $i.e.\ R^{'} = 9 \times 20 = 180\Omega$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.