(i) Define term wavefront. State Huygen.s principle.
(ii) consider a plane wavefront incident on a thin convex lens. Draw a proper diagram to show him the incident wavefront traverses throught the lens and after refraction focuses on the focal point of the lens, giving the shape of the emergent wavefront.
(iii) When light travels from a rarer to a denser medium, it loses speed. Does, this loss imply a reduction in energy carried by the light waves.