Question

A wire of radius 'r' has resistance R. If it is stretched until its radius is 1/2 the original value,then find its resistance and resistivity.

Answer 1

Resistance = ρ L/A

is A become A/2
then 
new R = ρL/(A/2)
=2(ρL/A)

so resistance become 2 times

Answer 2

new resistance is 16 times the first one and resistivity is same because of same material