A: 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.
R: Waves diffracted from the edge of the circular obstacle interfere constructively at the centre of the shadow producing a bright spot.

Assertion (A) : When tiny circular obstacle is placed in the path of light from some distance, a bright spot is seen at the centra of the shadow of the obstacle. Reason (R ) : Destructive interference occurs at the centre of the shadow.

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 central 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 7 m partition wall in a room 10 m high. If both light and sound waves can bend around obstacles, how is it that the students are unable to see each other even though they can converse easily (e) Ray optics is based on the assumption that light travels in a straight line. Diffraction effects (observed when light propagates through small apertures/slits or around small obstacles) disprove this assumption. Yet the ray optics assumption is so commonly used in understanding location and several other properties of images in optical instruments. What is the justification?

A man running along a circular track has the speedof 10 km per hour. A source of light is at the centre of the circular track. A wall is along the tangent to the circular track at the point from which he starts.What is the speed of the shadow of the man on the wall when he covers 1/8th of the track? (Assume thetrack to be a line.)

On a particle moving on a circular path with constant speed v , light is thrown from a projectors placed at the centre of the circular path. The shadow of the particle is formed on the wall. The velocity of shadow up the wall is