Question

Define the term wavefront. State Huygens principle. Consider a plane wave front incident on a thin convex lens. Draw a proper diagram to show how the incident wave front traverses through the lens and after refraction focuses on the focal point of the lens, giving the shape of the emergent wave front.

Answer 1

Definition : Locus of all points which oscillate in phase.

(i) Huygens Principle : Each point of the wave front is the source,of a secondary disturbance and the wavelets emanating from these points spread out in all directions. These travel with the same velocity as that of the original wave front. 

(ii) The shape and position of the wave front, after time 't', is given by the tangential envelope to the secondary wavelets.