If the length of the wire is changed its resistance would obviously change
and we know that resistance is directly proportional too length
Doubling the length will double the resistance, but the wire also must
get thinner as it is stretched, because it will contain the same amount
of metal in twice the length.
The volume of a cylinder is length * cross sectional area, but in
order to find the new cross section, you need to consider what the wire
is made of. Most materials resist a change in volume more than they
resist a change in shape, and because of that, they lose less volume
than otherwise would be expected when stress is applied.
In the case of the stretched wire, its density will be less after
stretching than it was before. This means that the volume of space
occupied by the metal in the wire expands, due to the cross sectional
area not shrinking in proportion to the stretch of its length. The
amount of reduction in cross section is determined according to
Hope this helped u