Huygens’ Principle explains the bending of light around obstacles—known as diffraction—by treating every point on a wavefront as a source of new, tiny wavelets that spread out in all directions.
When a light wave encounters an obstacle or a narrow opening:
- Each point at the edge of the obstacle or slit acts like a source of these secondary wavelets.
- These wavelets continue to spread into the region behind the obstacle, even where the original wavefront would have been blocked.
- As these secondary wavelets overlap and combine, they form a new wavefront that curves or bends around the edges.
This behavior is most noticeable when the obstacle or slit is comparable in size to the wavelength of light. In such cases, light doesn’t travel strictly in straight lines but spreads into the shadow region, producing interference and fringe patterns.
Thus, Huygens’ Principle gives a wave-based explanation for why light bends around corners or through small openings, a phenomenon that cannot be explained by ray theory alone. It supports the wave nature of light and is essential for understanding diffraction effects in optics.