NCERT · Class 12 · Physics · Wave OpticsState Huygens' Principle.

Huygens' Principle is a geometrical construction used to determine the shape of a wavefront at any subsequent time from its known shape at any previous time. It states that: 1. Every point on a given wavefront acts as a fresh source of secondary disturbance, emitting secondary spherical waveslets in all directions with the speed of light in that medium. 2. The envelope of these secondary wavelets, tangential to them in the forward direction at any later time, gives the new position and shape of the wavefront.