(a) When monochromatic light is incident on a surface separating two media, the reflected and refracted ligth both have the same frequency as the incident frequency. Explain why ?
(b) When light travels from a rarer to a denser medium, it loses speed. Does the reduction in speed imply a reduction in energy carried by the light wave ?
( c) In the wave picture of light, intensity of ligth is determined by the square of amplitude of wave. What determines the intensity of light in teh photon picture of light ? (NCERT Solved Example)

Explanation

(a) The refelction and refraction of light occur on account of interaction of light with the atoms of the surface of separation. These atoms can be regarded as oscillators.
Light incident on the interface forces the atomic oasillators to osillate with frequency of incident light. As frequency of light emitted by these (charged) oscillators is equal to their own frequency of osillation, therefore, relfected and refracted light have the same frequency as that of incident light.
(b) No, energy carried by the wave does not depend on its speed. Instead, it depends on the amplitude of wave.
( c) In the photon picture of light, the intensity of light at a point is determined by the number of photons per unit area around the point.