Wave Optics Question 9
Question 9 - 2024 (30 Jan Shift 1)
The diffraction pattern of a light of wavelength $400 \mathrm{~nm}$ diffracting from a slit of width $0.2 \mathrm{~mm}$ is focused on the focal plane of a convex lens of focal length $100 \mathrm{~cm}$. The width of the $1^{\text {st }}$ secondary maxima will be :
(1) $2 \mathrm{~mm}$
(2) $2 \mathrm{~cm}$
(3) $0.02 \mathrm{~mm}$
(4) $0.2 \mathrm{~mm}$
Show Answer
Answer: (1)
Solution:
Width of $1^{\text {st }}$ secondary maxima $=\frac{\lambda}{a} \cdot D$
Here
$a=0.2 \times 10^{-3} \mathrm{~m}$
$\lambda=400 \times 10^{-9} \mathrm{~m}$
$D=100 \times 10^{-2}$
Width of $1^{\text {st }}$ secondary maxima
$=\frac{400 \times 10^{-9}}{0.2 \times 10^{-3}} \times 100 \times 10^{-2}$
$=2 \mathrm{~mm}$
