Question

The resistance of a wire is 20 ohm.It is streched that the length become 3 times then the new resistance will be

Answer 1

The new R will be 9 times the previous one ...

That is

180 ohm

Answer 2

$\tt \: \blue{Resistnace \: of \: the \: original \: wire } \\ \bf \: R = \frac{ ρL}{A}, \: \: \sf \: where \: A= \frac{V}{L} \\ \\ \bf ⟹ R = \frac{ρL²}{V} \\ \\ \cal \small { Now \: its \: length \: is \: stretched \: such \: that \: new \: length }\\ \rm L′ = 3L \\ \\ \tt \: {Thus \: resistance \: of \: the \: wire} \\ \rm \: R′ = \frac{ρ(3L)²}{V} = 9R \\ \\ \red{ \small{ \bf Hence ,\: \: resistance \: becomes \: 9 \: times \: the \: initial \: resistance \ i.e \ 180\ Ω.}}$