question_answer

How is a wavefront different from a ray? Draw the geometrical shape of the wavefronts when (i) light diverges from a point source, and (ii) light emerges out of convex lens when a point source is placed at its focus.                                               

Answer:

                A wavefront is a surface obtained by joining all points vibrating in the same phase. A ray is line drawn perpendicular to the wavefront in the direction of propagation of light wave. The wavefronts of light emerging from a point source are spherical as shown in Fig. (a). When a point source is placed at the focus of a convex lens, the emerging light has plane wavefronts, as shown in Fig. (b).