Question

Explain the construction and propagation of a spherical wavefront using Huygens's principle.

Explain the construction of a spherical wavefront by using Huygens’ principle.

Answer 1

A spherical wavefront is generated when the light source is at a finite distance from the observation point.

Let PQ be a spherical wavefront due to point source 'S' at time t = 0. We wish to find its position after time t.

For this, we take a number of points A, B, C, and D on PQ. According to Huygen's principle, they act as a secondary source and emit secondary wavelets. Let c be the speed of light in the medium. In time t, each wave will describe the same distance ct.

Taking ct as a radius, draw a circle around points A, B, C, and D, then draw the common tangent P'Q' to all secondary waves as shown in the figure. The P'Q' will represent the new spherical wave front.