Match the LIST-I with LIST-II
| LIST-I (Physical Process) | LIST-II (Physical Action) | ||
| A. | Wave front acts | I. | turns around corners |
| B. | Monochromatic light through Young's double slits produces | II. | a broad pattern with a central bright maximum |
| C. | Light spreading out from a narrow slit | III. | as a source of secondary wavelets |
| D. | A single narrow slit illuminated by a monochromatic source | IV. | equally spaced interference fringes |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → A-III, B-IV, C-I, D-II
Each entry describes a result of the wave nature of light: Huygens’ principle, interference and diffraction.
(A) Wave front acts — this matches (III) as a source of secondary wavelets. By Huygens’ principle every point on a wavefront sends out secondary wavelets, whose common envelope gives the wavefront a moment later.
(B) Monochromatic light through Young’s double slits produces — this matches (IV) equally spaced interference fringes. The two slits act as coherent sources, and the bright and dark fringes are separated by the same fringe width \( \beta = \lambda D/d \).
(C) Light spreading out from a narrow slit — this matches (I) turns around corners. This bending of light round the edges of an obstacle or aperture is diffraction.
(D) A single narrow slit illuminated by a monochromatic source — this matches (II) a broad pattern with a central bright maximum. The single-slit diffraction pattern has a wide central maximum, twice as wide as the weaker secondary maxima on either side.
NCERT (2026-27):
Huygens Principle – “… Now, according to Huygens principle, each point of the wavefront is the source of a secondary disturbance and the wavelets emanating from these points spread out in all directions with the speed of the wave.”
Interference of Light Waves and Young’s Experiment – “… Equations (10.13) and (10.14) show that dark and bright fringes are equally spaced.”
The Single Slit – “… Even before Young, early experimenters – including Newton – had noticed that light spreads out from narrow holes and slits. It seems to turn around corners and enter regions where we would expect a shadow.”
The Single Slit – “… When the double slit in Young’s experiment is replaced by a single narrow slit (illuminated by a monochromatic source), a broad pattern with a central bright region is seen.”