Waves exhibit diffraction when they encounter barriers, bending and spreading into regions beyond the obstacle.

Diffraction is a fundamental property of waves, encompassing light, sound, and water waves. It describes the phenomenon where waves bend around obstacles or disperse after passing through a gap or slit. This bending or spreading becomes particularly pronounced when the dimensions of the obstacle or the width of the gap are comparable to the wavelength of the wave.

When a wave encounters a barrier with an opening or an obstacle, the wavefronts—defined as the lines or surfaces across which the wave maintains a constant phase—interact with the barrier. If there is a gap in the barrier, the wavefronts at this opening act as new sources of waves. These newly generated waves, often referred to as secondary wavelets, emanate from the gap, forming a new pattern known as a wavefront. This process of waves spreading out after passing through a gap is what we call diffraction.

The degree of diffraction, or how much the wave bends, is influenced by both the wavelength of the wave and the dimensions of the barrier or gap. When the wavelength is significantly smaller than the size of the barrier or gap, diffraction is minimal, and the wave primarily continues in a straight path. Conversely, if the wavelength is comparable to or larger than the size of the barrier or gap, substantial diffraction occurs, causing the wave to spread more widely.

In the case of an obstacle, waves bend around it and continue to propagate on the other side, creating a region known as the shadow zone. This shadow zone is not entirely devoid of waves (or silent in the case of sound) since the diffracted waves partially fill in this area. The extent of the shadow zone is determined by both the wavelength of the wave and the dimensions of the obstacle.

In conclusion, diffraction is a remarkable phenomenon that enables waves to bend around obstacles and spread out after passing through gaps. It is a crucial concept in wave physics, with significant implications in various fields, such as optics, acoustics, and water wave dynamics.