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Huygens principle states that

1) Every point on a given wavefront may be considered as a source of secondary wavelets which spread out with the speed of light in that medium. 2) The new wavefront is the forward envelope of secondary wavelet at that instant.

What does this actually mean in both theoretical and practical view? Does this explain in this way: Taking sun as a source, As the light from sun reaches every object, Do each & every object actually act as a new source of that light"..? Or a ray of light inside a room causes its walls to reflect the light. Then, do the walls act as a new source?

Explanation and examples related to both principles would be helpful...

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up vote 3 down vote accepted

One thing that the Huygens principle means, and I think it is this that you're getting at, is that the propagation of a wavefront is independent of where the light actually came from.

So yes, when a ray of light inside a room reflects off the walls, the walls act as a new source. If the original light source didn't exist, but the walls emitted a wavefront with exactly the same amplitude and phase as before, then you wouldn't be able to tell the difference.

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What it means from a practical view is the same thing is means from an abstract view: diffraction and refraction and all the clever things you can do with them.

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