Question

In a single slit diffraction experiment, 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? State two points of difference between the interference pattern obtained in Young’s double slit experiment and the diffraction pattern due to a single slit.

Answer 1

The waves diffracted at the edge of circular obstacle produce constructive interference at the centre of the shadow; producing a bright spot.

Difference between Interference and Diffraction

	Interference	Diffraction
1.	All bright fringes are of equal intensity.	The central maximum has maximum intensity and the intensity of secondary maxima goes on decreasing with increase of order.
2.	Fringe width of all fringes are equal.	The width of central maximum is maximum and goes on decreasing with increase of order of secondary maxima.