Question

A parallel beam of light strikes a piece of transparent glass having a cross section as shown in the figure below. Correct shape of the emergent wavefront will be(figures are schematic and not drawn to scale)

A.
B.
C.
D.

Answer 1

Hint: Here we use the concept of Huygens principle. According to the theory of wavefront waves move in such a way that direction of propagation is perpendicular to the wavefront. In every point on a wavefront is the source of spherical wavelets which spread out in the forward direction with the speed of light. The sum of these spherical wavelets can form the wavefront.

Complete step by step solution:
As we know that the rays of light will travel more in air than glass medium. If the glass medium is greater than the wavefront will be slack. Hence the shape of the emergent wavefront will be the figure given as,


Hence option A is the correct answer.

Note: According to Huygens principle the light is the form of wave that propagates through space like ripples form in the water or sound in air. Therefore, the light spread out like a wave in all the directions from a source. The locus of points that travel some distance in a fixed time interval is known as a wavefront. Hence from a point source of light, the locus of points is a sphere that light has travelled during a fixed time period. The concepts of diffraction of light, interference of light, etc all are proved by Huygens principle.