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 5000 is incident on the slit. The first secondary maximum is observed at an angle of (a) sin ⁻ 1 (1/2) (b) sin ⁻¹(3/4) (c) sin ⁻¹(1/4) (d) sin ⁻¹(2/3)

Answer: (b). First minimum: asin 30° = λ ⇒ a = 2λ. First secondary maximum: asin θ = (3λ)/(2) ⇒ sin θ = 3/4. So the answer is (b) sin ⁻¹(3/4).

In a diffraction pattern due to a single slit of width a, the first… | NEET 2016 (Phase 1)

Q77NEET 2016 · PHASE 1Easy

Diffraction at a Single Slit

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 5000 $\text{\AA}$ is incident on the slit. The first secondary maximum is observed at an angle of

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Answer: (b)

First minimum: $a\sin 30^\circ = \lambda \Rightarrow a = 2\lambda$ .
First secondary maximum: $a\sin\theta = \dfrac{3\lambda}{2} \Rightarrow \sin\theta = \dfrac{3}{4}$ .
So the answer is (b) $\sin^{-1}\left(\frac{3}{4}\right)$ .

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