Question

a wire of resistivity P is pulled to double its length what will be its new resistivity

Answer 1

HEY DEAR ...

R=ρL/A
When L becomes 2L, A becomes A/2
New R=ρ 2L/A/2
           =4 ρL/A
           =4 R
New resistance becomes 4 times the original one.
But, resistivity remains the same as it is the property of the substance and does not change with length or area.

HOPE , IT HELPS ...

Answer 2

Let the initial Resistivity be p (since *rho* isn't available on my on-screen keyboard).
R = p•A/L
p = R • (L / A) ---------- (I)
since, Length L is doubled, Area A is halved, the new Resistivity is p',
p' = R • (2L / A/2)
p' = 4 [R • (L / A)]
p' = 4•p ----------(from (I))
Therefore, New Resistivity becomes 4 times the initial Resistivity.