Question

A fixed volume of iron is drawn into a wire of length $l.$ The extension $x$ produced in this wire by a constant force $F$ is proportional to:

• A. $l$
• B. $l^{2}$
• C. $\frac{1}{l}$
• D. $\frac{1}{l^{2}}$

Answer 1

Answer: (B)

$l^{2}$

Answer 2

$\begin{pmatrix}\text { as } V=A l \\\ \text { so } A=\frac{V}{l}\end{pmatrix}$
Extension $x=\frac{F l}{A Y}$
$=\frac{F l^{2}}{V Y} \propto l^{2}$