A wire of resistance 4 Ω is stretched to twice its original length. The resistance of stretched wire would be
Resistance of a wire,
When wire is stretched twice, its new length be ‘l’. Then l'=2l
On stretching volume of the wire remains constant.
∴ lA=l'A'where A' is the new cross-sectional area Or A'=1l'A=12lA=A2
∴ Resistance of a stretched wire is R'=ρl'A'=ρ2lA/2=4ρlA