Interference and diffraction are both phenomena due to the wave nature of light, but they differ in origin and behavior:
Interference is the phenomenon where two or more coherent light waves (i.e., having constant phase difference and same frequency) superpose to produce a resultant intensity pattern. This pattern shows constructive interference (bright fringes, where waves are in phase) and destructive interference (dark fringes, where waves are out of phase). It typically involves two or more sources, like in Young's double slit experiment.
Diffraction, on the other hand, occurs when a wave encounters an obstacle or a slit that is comparable in size to its wavelength, causing the wave to bend around the edges and spread out. The diffraction pattern arises due to the interference of secondary wavelets (from different parts of the same wavefront), even when there's only one slit or obstacle. It is explained by Huygens' principle.
In summary:
- Interference: Superposition from two coherent sources → clear alternate bright and dark fringes.
- Diffraction: Bending and spreading from edges of one source/slit → central maximum is the brightest and widest, with decreasing side maxima.
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