Principio di Huygens en
From "Physics, Waves, Music": a website about the physics of waves and sound, acoustics of musical instruments, musical scales, harmony and music.
| AI-translated from Italian. Original page: Principio_di_Huygens |
Huygens' principle
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In 1678 the Dutch scientist Christiaan Huygens formulated a "heuristic" rule that made it possible to interpret light phenomena as wave phenomena. In open contrast with Newton's corpuscular theory of light, Huygens derived from his principle a consistent wave interpretation of all the light phenomena then known.
In Huygens' own words [1] "...each particle of matter in which a wave spreads ought not to communicate its motion only to the next particle which is in the straight line drawn from the luminous point, but that it also imparts some of it necessarily to all the others which touch it and which oppose themselves to its movement. So it arises that around each particle there is made a wave of which that particle is the centre" In short, the principle states that: "All the points of a wavefront can be considered point sources of secondary spherical waves with the same frequency as the main wave. After a time the new position of the front will be the envelope surface of these secondary waves" The image alongside clarifies this. |
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Although it was born to interpret light phenomena, Huygens' principle actually provides a powerful heuristic tool for predicting the behaviour of any wave phenomenon.
For example, to explain the straight-line propagation of light (certainly a strong point of the corpuscular interpretation of light), Huygens' principle uses the construction alongside, which undoubtedly looks contrived compared with the simplicity of the explanation in terms of corpuscles. To see Huygens' principle at work in other situations, visit the pages on reflection, refraction and diffraction. You will discover that the explanatory power of the principle lies precisely in its great versatility and generality. |
Experiments on Huygens' principle
On the following pages you will find instructions for carrying out, in the 2D Waves virtual laboratory, a series of experiments that illustrate, once again, the explanatory power of the principle.
Check your understanding
According to Huygens' principle, how is the position of a wavefront one instant later constructed?
Answer. Each point of the present front is regarded as a source of secondary spherical waves, with the same frequency and the same speed as the wave. After a time each secondary wave has radius ; the new front is the surface that envelops them, that is, touches them all on the side towards which the wave advances.A plane wave reaches a wall with a gap narrower than the wavelength. What does Huygens' principle predict for the wave beyond the wall?
Answer. Of the part of the front reaching the wall, only the part passing through the gap remains active, and it behaves as a single, almost point-like secondary source. Beyond the wall, therefore, a circular wave (spherical, in space) centred on the gap propagates, reaching also the regions that would remain in shadow with propagation along straight rays: this is diffraction.- ↑ C. Huygens, Traité de la Lumière, Paris, Gauthier Villars, 1920, p. 19
