Diffraction — Predicted 2026

AI-Predicted Question Angles for UPSC 2026

Based on trend analysis, current affairs, and recurring themes in Diffraction.

Combined Interference and Diffraction (Double Slit with finite slit width)

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While NEET primarily focuses on single-slit diffraction and Young's double-slit interference separately, a slightly more advanced conceptual question could combine the two. For instance, asking about the missing orders in a double-slit pattern when the slit width is comparable to the slit separation. This tests a deeper understanding of how the diffraction envelope modulates the interference pattern. Students should be aware that the intensity of interference fringes is modulated by the single-slit diffraction pattern.

Effect of Medium on Diffraction Pattern

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Most diffraction problems assume the experiment is conducted in air or vacuum. A slightly trickier question could involve performing the experiment in a different medium (e.g., water). Since the wavelength of light changes in a medium ($\lambda' = \lambda/n$, where $n$ is the refractive index), this would affect the width of the central maximum and angular positions. This tests the understanding that wavelength is the critical factor in diffraction and it changes with the medium.

Qualitative Analysis of Diffraction from Different Aperture Shapes

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While single-slit and circular apertures are standard, a conceptual question might briefly touch upon diffraction patterns from other simple shapes (e.g., a square aperture or a pinhole). This would likely be qualitative, asking about the general shape of the pattern (e.g., a square aperture produces a square-like pattern). This tests a broader conceptual understanding of how aperture geometry influences the diffraction pattern, without requiring complex calculations.

Resolving Power of Human Eye

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Questions on resolving power are common, but specifically applying the Rayleigh criterion to the human eye (considering the pupil as a circular aperture) is a practical and relatable application. This could involve calculating the minimum distance between two points on an object that the eye can resolve at a certain viewing distance, or the minimum angular separation. It combines the diffraction concept with human physiology.