Concept of wavefront:
i. According to Huygens’ theory, light travels in the form of waves which are emitted from the source.
ii. Consider a point source S of light situated in air or vacuum. Light waves spread out in all possible directions from the source of light with same speed c.
iii. After time t seconds, each light wave covers a distance equal to ct.
iv. Draw a spherical surface by considering radius ct and S as its centre. This surface cuts waves of light at different points A, B, C, D, E etc.
v. All the points on this surface are in the same phase. It is an equiphase surface. Such a surface is called spherical wave surface or a spherical wavefront.
