Phenomenon of diffraction occurs

Explanation

When light passes through a small opening or by the edge of an Obstacle and falls on a screen, the principle of rectilinear propagation of light from geometrical optics predicts a sharply defined shadow.
However, some of the light deviates from its rectilinear path and penetrates into the region of the geometrical shadow. This is a generel characteristic of wave phenomena and occurs whenever a portion of the wavefront is obstructed in some way. This bending of light waves at an edge into the region of the geometrical shadow is called diffraction of light.