# Fresnel diffraction is produced due to light rays falling on a small obstacle. The intensity of light at a point on a screen beyond an obstacle depends on

(a) the focal length of lens used for observation

(b) the number of half-period zones that superpose at the point

(c) the square of the sum of the number pf half period zones

(d) the thickness of the obstacle

b) the number of half-period zones that superpose at the point