Identify the correct statement for the single slit diffraction pattern.
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → If the width of single slit is made twice of its original width, then the half angular width of the central maximum is reduced to half of its original value.
In single-slit diffraction the first minimum is at \( \sin\theta = \lambda/a \), so the half angular width of the central maximum is \( \theta \approx \lambda/a \), inversely proportional to the slit width a.
Option (1) All bright bands have the equal intensities. — Incorrect. The secondary maxima get fainter away from the centre.
Option (2) If the width of single slit is made twice of its original width, then the half angular width of the central maximum is reduced to half of its original value. — Correct. Doubling a halves \( \theta \).
Option (3) The formation of diffraction pattern is due to superposition of the secondary wavelets from different parts of the two different wavefronts. — Incorrect. The wavelets come from the same wavefront.
Option (4) All diffraction bands have equal width. — Incorrect. The central maximum is twice as wide as the others.
NCERT (2026-27):
The Single Slit – “… We are treating different parts of the wavefront at the slit as secondary sources.”
Summary – “… 5. A single slit of width a gives a diffraction pattern with a central maximum. The intensity falls to zero at angles of \( \pm\frac{\lambda}{a}, \pm\frac{2\lambda}{a} \), etc., with successively weaker secondary maxima in between.”