Question

a wire is doubled over itself what will be the new resistance and resistivity with the original resistance is 10 Ohm

Answer 1

R=rho*l/a
Resistivity will be same while resistance will be double =20ohm

Answer 2

When wire is doubled over itself, area is doubled and length is halved.

Resistance is proportional to Length and inversaly proportional to Area.

So

R` = R(1/2)/2

R'=R/4

R' = 10/4 =2.5 Ohm