Question

Two plane wavefronts of light, one incident on a thin convex lens and another on the refracting face of a thin prism. After refraction at them, the emerging wave fronts respectively become
A. Plane wave front and plane wave front.
B. Plane wave front and spherical wave front.
C. Spherical wave front and plane wave front.
D. Elliptical wave front and spherical wave front.

Answer 1

If a small part of the spherical either cylindrical wave front tends to be plane while the point source either linear light source is at such a wide wavelength, this very wave front is called a plane wave front. The spherical wave front is a component of the surface of the spherical wave.

Complete step-by-step solution:
Given that there are two plane wave fronts of light where one incident on a thin convex lens and another incident on the refracting face of a thin prism. We need to find out what happens to the emerging wave fronts after refraction.
Once the wave passes the prism, the outer parts first pass into the air as well as first speed up. This means that when the first the outer parts pass out more easily and then the curvature of the wave is further improved such that the light converges more intensely.
So, the emerging wave front will be a spherical wave front. It is the bottom half of the wave that reaches the glass first when the wave enters the prism so that this portion of the wave is slowed down suddenly. This suggests that the upper component shifts quickly and therefore the wave front bends when it approaches the lens, so we get a slanted plane wave front.
So, the emerging wave front will be plane wave front.
Hence, option C is correct.

Note: It is the core of the wave which reaches the glass first when the wave strikes the rim, so that this section of the wave is slowed down. This indicates the 'catch up of the major shift of the wave such that the curvature rises to create a converging bear.