Match List I with List II
| LIST I | LIST II | ||
|---|---|---|---|
| A. | Plane wavefront incident on a convex lens | I. | Diffraction pattern appears |
| B. | Plane wavefront incident on a concave lens | II. | Diverging spherical wavefront emerges |
| C. | One slit is closed in YDSE | III. | Interference pattern becomes less sharp |
| D. | In YDSE if width of source slit is increased | IV. | Converging spherical wavefront emerges |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → A-IV, B-II, C-I, D-III
(A) Plane wavefront incident on a convex lens — this matches (IV) Converging spherical wavefront emerges. The centre of a convex lens is thickest, so the part of the wavefront passing there is delayed most; the emerging wavefront is curved inwards and converges to the focus.
(B) Plane wavefront incident on a concave lens — this matches (II) Diverging spherical wavefront emerges. The centre of a concave lens is thinnest, so the edges are delayed most and the emerging wavefront spreads out as if from a point.
(C) One slit is closed in YDSE — this matches (I) Diffraction pattern appears. With only one slit there is nothing to interfere with, and the light spreads out in the single-slit diffraction pattern.
(D) In YDSE if width of source slit is increased — this matches (III) Interference pattern becomes less sharp. Different parts of a wide source slit produce fringe patterns that are shifted relative to one another, and they overlap, so the fringes get blurred.
Note: Items (A), (B) and (C) of this question are from the latest textbook (2026-27). Item (D), that a wider source slit makes the interference pattern less sharp, is printed only in the pre-rationalised textbook (2022-23). It was removed from the latest book, but Young’s double-slit experiment is still in the CUET 2026 syllabus, so do not skip it.
NCERT (2026-27):
Reflection of a Plane Wave by a Plane Surface – “… In Fig. 10.7(b) we consider a plane wave incident on a thin convex lens; the central part of the incident plane wave traverses the thickest portion of the lens and is delayed the most. The emerging wavefront has a depression at the centre and therefore the wavefront becomes spherical and converges to the point F which is known as the focus. … In a similar manner, we can understand refraction and reflection by concave lenses and convex mirrors.”
The Single Slit – “… In the double-slit experiment, we must note that the pattern on the screen is actually a superposition of single-slit diffraction from each slit or hole, and the double-slit interference pattern.”
NCERT (Pre-rationalised edition, 2022-23):
Interference of Light Waves and Young’s Experiment – “… (e) Same as in (d). As the source slit width increases, fringe pattern gets less and less sharp.”