Question

A 8ohm resistance wire is stretched to double its lenght .the new reistance of wire will be

Answer 1

The new resistance will be 32 ohm
Just apply R is directly proportional to L^2

Answer 2

volume of wire before stretching= volume of wire after stretching
Area of cross section × length = Area of cross section × length
A×L=a×l
A×L=a×2L
A = a×2
A/2= a

Resistivity of the both wire will be same as they are made up of same material.
P=p
R×A/L = r×a/l
8×A/L = r×A/4L
8 = r/4
32= r


Therefore, the new resistance will be 32 Ohm.