What is the shape of the wavefront in each of the following cases? a. Light diverging from a point source. b. Light emerging out of a convex lens when a point source is placed at its focus. c. The portion of the wavefront of light from a distanct star intercepted by the Earth.

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

Answer the following questions: a. In a single slit diffraction experiment, the width of the slit is made double the original width. How does this affect the size and intensity of the cenral diffraction band? b. In what way is diffraction from each slit related to the interference pattern in a double slit experiment? c. When a tiny circular obstacle is placed in the path of light from a distant source, a bright spot is seen at the centre of the shadow of the obstacle. Explain why. d. Two students are separated by a 7m partition wall in a room 10 m high. If both light and sound waves can bend around obstacles, howare the students unable to see each other even though they can converse easily. e.Ray optics is based on the assumption that the light travels in a straight lin. Diffraction effects (observed when light propagates through small apertures/slits a or around small obstacles) disprove this assumption. Yet the ray options assumptioni is so commonly used in understanding location and several other properties of images in optical instruments. What is the justification?