Question

a wire of resustance 20 ohm is uniformly streched so that its length becomes two times the original length find the resistance of the wire after elongation

Answer 1

If no change in area of crossection assumed, then the resistance of the wire after elongation will be twice that of the earlier. i.e. 40ohm. Unless the change in area of crossection existed, and the area of crossection if changed to half of what it was before, then final resistance of the wire will become, 4 times of the initial value. i.e. 80ohm