Question

Kabir and Neha conducted experiments on light as part of their school project. Both of them worked with the same source of monochromatic yellow light. Both obtained patterns on the screen which consisted of alternate bright and dark bands.

The images below depict their results.

1. Identify the phenomenon observed by Neha.
2. The teacher asked Kabir to replace monochromatic yellow light with white light. What would be Kabir’s observation now?
3. What conclusion would be drawn by Kabir and Neha about the nature of light?

Answer 1

(i) The phenomenon observed by Neha is Diffraction of light (specifically, single-slit diffraction). Single‑slit diffraction (a broad central bright band with much weaker side maxima and dark bands). This pattern is characteristic of diffraction when the aperture size is comparable to the wavelength.

(ii) The central fringe would remain white (the zero‑order maximum), while the nearby fringes would become coloured (a few coloured side fringes) and farther out the different colours overlap into almost uniform illumination. This is because different wavelengths produce slightly different fringe positions (β ∝ λ).

(iii) The conclusion drawn by both Kabir and Neha is that light behaves like a wave. Interference and diffraction arise from the superposition of waves, so light behaves as a wave. From the white‑light result, they would also conclude that white light is made of many wavelengths (colours) since different colours produce different fringe positions.