Which of the following correctly represents the refracted wavefront A'B'.
Answer & explanation
Correct answer: option 1
The correct answer is Option (1)
By Huygens’ principle, a plane wavefront stays plane after passing through a prism, but it is turned. The part of the wavefront that crosses the thicker part of the prism travels through more glass, where light moves more slowly, so it falls behind the part that crosses the thinner part.
The emerging wavefront is therefore plane but tilted, and the rays, which are normal to it, are bent towards the base of the prism. Only the first figure shows a plane tilted wavefront A′B′ with the rays bent in this way.
NCERT (2026-27):
Reflection of a Plane Wave by a Plane Surface – “… In Fig. 10.7(a) we consider a plane wave passing through a thin prism. Clearly, since the speed of light waves is less in glass, the lower portion of the incoming wavefront (which travels through the greatest thickness of glass) will get delayed resulting in a tilt in the emerging wavefront as shown in the figure.”
