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 graph is a straight line?

• A

  $∆l$ versus $1/l$
• Correct answer
  B

  $∆l$ versus $l^2$
• C

  $∆l$ versus $1/l^2$
• D

  $∆l$ versus $l$

Hence, the correct answer is option: 'B'.