Copper of fixed volume V is drawn into wire of length ι. When this wire is subjected to a constant force F, the extension produced in the wire is ∆ι. Which of the following graphs is a straight line?

As V=Al                                      . . . .(i)where A is the area of cross - section of the wire. Young's modulus, Y=(F/A)(Δl/l)=FlAΔlΔl=FlYA=Fl2YV  (Using (i)Δl∝l2 Hence, the graph between Δl and l2 is a straight line.