Question

a given wire stretches to reduce its diameter to half its orginal value what will be its new resistance

Answer 1

I'm think it is high resistance than before
I hope ..

Answer 2

Hey mate here is your answer.....!!

Taking into account that the resistance R of a wire of length L, diameter d and material of electrical resistivity rho, is inversely proportional to the cross section A of the wire,

R = rho L / A

being

A = π d^2 / 4

it could be said that if the diameter is reduced by half (d/2) , the area of ​​the cross section is reduced four times (A/4) and then, the resistance would increase four times (i.e., the new resistance will be 4R).

WRONG ! There is something more, something very important.

The process to reduce the diameter is called "drawing" (“trefilado”, in Spanish), which in this case corresponds to a cold work of 75% (% CW = 75), which is a huge change which produces a lot deformation in the grains of the polycrystalline material that composes the conductor. This large number of deformation defects greatly increases the electrical resistivity rho of the material, and therefore, the answer to the question is

THE NEW RESISTANCE WILL BE GREATER THAN 4R,


Regards
Riyanshu.....!!☺