Question

If a wire is stretched twice its length, how is its resistance and specific resistance change?

Answer 1

Initially R=ρL/A .when we stretch the wire to double it's original length i.e. now 2L the area will become half i.e. now A/2 as the volume before and after will be same.Now putting the value the new resistance is given by R'=ρ2L/A÷2=4ρL/A=4R, i.e. the resistance of the wire will become 4times it's original resistance.
Resistivity or specific resistance is a property of a material it doesn't depend on the area or the length of that material.