First slide

Diffraction

Question

A parallel beam of monochromatic light of wavelength 5000 Å is incident normally on a single narrow slit of width 0.01 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

Moderate

A

$0^{o}$
B

$1 . 5^{o}$
C

$3^{o}$
D

$5^{o}$

Solution

First minima $\sin θ = \frac{λ}{d} = \frac{5 \times 10^{- 7}}{10^{- 5}}$
$\begin{array}{l} \sin θ = 5 \times 10^{- 2} \\ θ = .05 r a d = \frac{0.05 \times 180}{π} \\ = \frac{9}{3.14} = 3^{0} \end{array}$

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