### NEET Solved Paper 2019 Question 45

##### Question: A copper rod of 88 cm and an aluminium rod of unknown length have their increase in length independent of increase in temperature. The length of aluminium rod is $ ({\alpha _{Cu}}=1.7\times 10^{5}K^{1}and,{\alpha _{Al}}= $ $ ~2.2\times 10^{5}K^{1}) $ -[NEET 5-5-2019]

#### Options:

A) 88 cm

B) 68 cm

C) 6.8 cm

D) 113.9 cm

## Show Answer

#### Answer:

Correct Answer: B

#### Solution:

$ \Delta {\ell_1}=\Delta {\ell_2} $

$ {\ell_1}{\alpha_1}={\ell_2}{\alpha_2} $

$ \frac{{\ell_1}}{{\ell_2}}=\frac{{\alpha_2}}{{\alpha_1}} $

$ \frac{88}{{\ell_a}}=\frac{2.2\times {10^{-5}}}{1.7\times {10^{-5}}} $

$ {\ell_a}=68cm $

Comment: In this question it should be difference in length instead of increase in length.