NEET Solved Paper 2014 Question 35

Question: A beam of light of $ \lambda $ = 600 nm from a distant source falls on a single slit 1 mm wide and the resulting diffraction pattern is observed on a screen 2 m away. The distance between first dark fringes on either side of the central bright fringe is [AIPMT 2014]

Options:

A) 1.2 cm

B) 1.2 mm

C) 2.4 cm

D) 2.4 mm

Show Answer

Answer:

Correct Answer: D

Solution:

From the figure, $ \tan \theta =\frac{x/2}{2} $ For small $ \theta $

and when $ \theta $ is counted in rad, $ \tan \simeq \theta $

So, $ \theta \simeq \frac{x/2}{2}\Rightarrow \frac{\lambda }{9}\simeq \frac{x}{4} $ $ x\simeq \frac{4\lambda }{a}\simeq \frac{4\times 600\times {10^{-9}}}{{10^{-3}}}m $ $ \simeq 24\times {10^{-4}}m $ $ \simeq 2.4\times {10^{-3}}m $ $ \simeq 2.4mm $