Question

A wire of length 10 cm and resistance 2 ohm is stretched to 30 cm then its resistance is?

Answer 1

$r = n ^{2} r$
since lenth is increased to 3 times n= 3

Answer 2

resistance = resistivity × length of the conductor /area
resistivity =resistance×area/length of the conductor=2×A/10=A/5
now the wire is stretched to 30 cm that is the length of the wire is increased by 3 times
therefore the area of the wire is divided by 3
therefore required resistance=resistivity×length of the wire/area
=A/5×30/A/3=18 ohm