JEE Main 2026 — Apr 4, Shift 1 — Physics solution

JEE Main2026Apr 4, Shift 1Physics

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
$2 \frac{D λ}{a}$
D
$3 \frac{D λ}{a}$

Solution

In single-slit diffraction the $n^{th}$ minimum sits at $y_{n} = \frac{nλ D}{a}$ (small-angle approximation).

Separation between $3^{rd}$ and $1^{st}$ minima:

$Δ y = y_{3} - y_{1} = \frac{3 λ D}{a} - \frac{λ D}{a} = \frac{2 λ D}{a} .$

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