Huygens’ Principle provides a clear wave-based explanation for both the laws of reflection and refraction, showing how these fundamental optical laws naturally arise from the way wavefronts propagate.
Relation to the Law of Reflection:
- When a wavefront hits a smooth surface, each point on the wavefront at the boundary acts as a source of secondary wavelets.
- These wavelets spread out and combine to form a new wavefront that moves away from the surface.
- The direction of this new wavefront corresponds to the angle of reflection, which is equal to the angle of incidence.
- This happens because the geometry of wavelet propagation ensures the reflected wavefront forms symmetrically, matching the classical law: angle of incidence equals angle of reflection.
Relation to the Law of Refraction:
- When the wavefront passes from one medium to another with a different speed of light, the secondary wavelets in the second medium move at a different speed.
- This difference causes the new wavefront in the second medium to bend at the interface.
- The bending angle follows Snell’s law, which relates the angles of incidence and refraction to the refractive indices of the two media.
- Huygens’ Principle explains this by showing how the changing speeds of secondary wavelets on either side of the boundary reshape the wavefront direction.
In essence:
- The laws of reflection and refraction emerge naturally from the way secondary wavelets spread and interfere at boundaries.
- Huygens’ Principle gives a physical, wave-based understanding of these laws, reinforcing that light behaves as a wave and explaining why these laws hold true for all wave phenomena.