## wave-optics Question 31

Question: Q. 10. (i) Write three characteristic features to distinguish between the interference fringes in Young’s double slit experiment and the diffraction pattern obtained due to a narrow single slit.

(ii) A parallel beam of light of wavelength $500 \mathrm{~nm}$ falls on a narrow slit and the resulting diffraction pattern is observed on a screen $1 \mathrm{~m}$ away. It is observed that the first minima is at distance of 2.5 $\mathrm{mm}$ away from the centre. Find the width of the slit.

A [Foreign 2014]

## Show Answer

Solution:

Ans. (i) Try yourself, similar to Q. 1 Short Answer Type Questions -I

(ii)

$$ y_{n}=\frac{n \lambda D}{d} $$

$$ \Rightarrow \quad d=\frac{n \lambda D}{y_{n}} $$

$\therefore \quad d=\frac{1 \times 500 \times 10^{-9} \times 1}{2.5 \times 10^{-3}} \mathrm{~m} \quad 1 / 2$

$d=2 \times 10^{-4} \mathrm{~m}(=0.2 \mathrm{~mm}) 1$

[CBSE Marking Scheme 2014]