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?

• A

  $∆\mathrm{l} \mathrm{versus}\frac{1}{\mathrm{l}}$

• B

  $∆l versus l^2$

• C

  $∆\mathrm{l} \mathrm{versus} \frac{1}{{\mathrm{l}}_2}$

• D

  $∆l versus l$