Wave Optics - Result Question 35
38. A parallel beam of monochromatic light of wavelength $5000 \AA$ is incident normally on a single narrow slit of width $0.001 mm$. The light is focussed by a convex lens on a screen placed in focal plane. The first minimum will be formed for the angle of diffraction equal to
(a) $0^{\circ}$
(b) $15^{\circ}$
(c) $30^{\circ}$
(d) $50^{\circ}$
[1993]
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Answer:
Correct Answer: 38. (c)
Solution:
- (c) For first minimum, a $\sin \theta=n \lambda=1 \lambda$
$\sin \theta=\frac{\lambda}{a}=\frac{5000 \times 10^{-10}}{0.001 \times 10^{-3}}=0.5$
$\theta=30^{\circ}$
