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

Young's modulus Y = StressStrainor Y = FA∆ll = FlA∆l⇒ ∆l = FlAY-------(i)The volume of wire V = Alor A = VlSubstituting the value of A from (ii) in equation (i) We get ∆l ∞ l2Hence the graph of ∆l versus l2 will give a straight line.