Question

A plane wave front is entering a lens is given in the figure

1. What is meant by a wave front

2. What are different types of wave fronts

3. Complete the diagram and draw the refracted wave front.

Answer 1

1. Locus of all points having same phase of vibration is called wavefront.

2. Spherical wavefront, cylindrical wavefront plane wave front

3. Wave frond through a thin convex lens:

Consider a plane wave passing through a thin convex lens. The central part of the incident plane wave travels through the thickest portion of lens. Hence central part get delayed. As a result the emerging wave frond has a depression at the centre. Therefore the wave front becomes spherical and converges to a point F.