Q

# Need explanation for: - Optics - NEET

In a diffraction pattern due to a single slit of width 'a', the first minimum is observed at an angle 30° when light of wavelength   is incident on the slit. The first secondary maximum is observed at an angle of:

• Option 1)

• Option 2)

• Option 3)

• Option 4)

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As we learnt in

Fraunhofer Diffraction -

$b\sin \theta = n\lambda$

- wherein

A condition of nth minima.

$b=$ slit width

$\theta =$ angle of deviation

For first minima; $b\sin \Theta =\lambda$

$\sin \Theta =\frac{\lambda }{b}$

since $\Theta = 30\:\lambda =\frac{b}{2}$

For $1^{st}$ secondary maxima

$b\sin \Theta ^{1}=\frac{3\lambda }{2}$

$\sigma r \sin \Theta ^{1}=\frac{3\lambda }{2b}=\frac{3}{4}$

$\Theta ^{1}=\sin ^{-1}\left ( \frac{3}{4} \right )$

Option 1)

Incorrect

Option 2)

Incorrect

Option 3)

Incorrect

Option 4)

Correct

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