Match List-I with List-II.
| List-I | List-II |
| 1. Huygens principle | A. Coherence |
| 2. Diffraction | B. Apparent depth |
| 3. Interference | C. Secondary wavelets |
| 4. Refraction | D. Bending of light |
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 1-C, 2-D, 3-A, 4-B
1. Huygens principle — This matches C. Secondary wavelets. Every point of a wavefront acts as a source of secondary wavelets. The common tangent (forward envelope) of these wavelets gives the wavefront at a later time.
2. Diffraction — This matches D. Bending of light. Light passing through a narrow slit or past an edge spreads out and bends into the region of geometrical shadow.
3. Interference — This matches A. Coherence. A stable interference pattern needs coherent sources, whose phase difference does not change with time. With incoherent sources the intensities just add up.
4. Refraction — This matches B. Apparent depth. Light from the bottom of a tank of water bends at the surface. So the bottom appears raised.
NCERT (2026-27):
Huygens Principle – “… 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. These wavelets emanating from the wavefront are usually referred to as secondary wavelets and if we draw a common tangent to all these spheres, we obtain the new position of the wavefront at a later time.”
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. These effects, known as diffraction, can only be properly understood using wave ideas.”
Coherent and Incoherent Addition of Waves – “Now if the two sources are coherent (i.e., if the two needles are going up and down regularly) then the phase difference φ at any point will not change with time and we will have a stable interference pattern; i.e., the positions of maxima and minima will not change with time.”
Refraction – “… Another familiar observation is that the bottom of a tank filled with water appears to be raised … For viewing near the normal direction, it can be shown that the apparent depth (h1) is real depth (h2) divided by the refractive index of the medium (water).”