Huygen's principle is a geometrical construction of a wavefront which is used to determine the position of a wavefront at a later time from its position at any instant. The principle is based on the following assumptions.
- Each point on the primary (given) wavefront acts as a source of secondary wavelets, the light waves sending out from secondary sources travel in all directions with the speed of light.
- The new position of the wavefront at any instant is given by the forward envelope of the secondary wavelets at that instant.
Yes, Huygen's principle can be applied to the sound wave in the air.