A slit of width a is illuminated by light of wavelength $\lambda$. The linear separation between $1^{\text{st}}$ and $3^{\text{rd}}$ minima in the diffraction pattern produced on a screen placed at a distance D from the slit system is ______.

JEE Main · 2026 · 04 Apr 2026 · Shift 1 · Wave Optics

A slit of width a is illuminated by light of wavelength

λ

. The linear separation between

1^{st}

and

3^{rd}

minima in the diffraction pattern produced on a screen placed at a distance D from the slit system is ______.

(A) $\frac{D λ}{a}$
(B) $1.5 \frac{D λ}{a}$
(C) $2 \frac{D λ}{a}$ ✓ Correct
(D) $3 \frac{D λ}{a}$

Answer: (C)

Solution

In single-slit diffraction the minima occur where

a sin θ = nλ

, so for small angles the

n^{th}

minimum lies at

y_{n} = \frac{n D λ}{a}

. The first minimum is at

y_{1} = \frac{D λ}{a}

and the third minimum at

y_{3} = \frac{3 D λ}{a}

. Their separation is

y_{3} - y_{1} = \frac{3 D λ}{a} - \frac{D λ}{a} = \frac{2 D λ}{a}

JEE Main · 2026 · 04 Apr 2026 · Shift 1 · Single correct option

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