### NEET Solved Paper 2014 Question 13

##### Question: Copper of fixed volume Vis drawn into wire of length $ l $ . When this wire is subjected to a constant force F, the extension produced in the wire is $ \Delta l $ . Which of the following graphs is a straight line? [AIPMT 2014]

#### Options:

A) $ \Delta l $ versus $ \frac{1}{l} $

B) $ \Delta l $ versus $ l^{2} $

C) $ \Delta l $ versus $ \frac{1}{l^{2}} $

D) $ \Delta l $ versus $ l $

## Show Answer

#### Answer:

Correct Answer: B

#### Solution:

For Hooke’s law. Young Modulus $ y=\frac{F/A}{\Delta l/l}=\frac{F\times l}{\Delta l\times A} $ $ V=A\times l $ =constant From Eqs. (i) and (ii),

$ y=\frac{F\times l\times l}{\Delta l\times V} $ ?(i) $ \Delta ,l=\frac{F}{V\times y}l^{2} $ ?(ii)

Þ $ \Delta l\propto l^{2} $