A wire of resistance ‘R’ is elongated n-fold to make a new uniform wire. The resistance of new wire

Volume will remain same.       lA=l'A' ⇒lA=nlA' ⇒A'=An Now take ratio of new and old values of resistances R'R=ρl'/A'ρl/A=nl/A/nl/A=n2 II method: If wire is elongated then R∝l2 ⇒R'R=l'l2⇒R'=Rnll2=n2R