# Tag Info

### Why exactly does diffraction occur?

For the full math, you can look up 'diffraction' and 'Huygens Principle' but here I will just post a quick observation that is enough to get a good physical intuition. Suppose we are considering ...
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### Why exactly does diffraction occur?

The first thing to realize is that waves only appear to travel. But when you look at a fish in the water, it becomes clear that the water only sloshes back and forth. Waves occur because the water ...
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### Question on wave interference?

Actually, you're completely right. Most treatments of the double slit involve some kind of simplification. The usual idea is that we approximate each slit in the double slit to be a point source, so ...
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### Why exactly does diffraction occur?

"Why are waves straight?" is the first question. Let's start with a model of waves where particles don't have much kinetic energy. They just have potential energy. Each location, if it has less ...
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### Why don't plane waves always expand according to Huygens' principle?

A plane wave, by definition, is already infinite in extent in the directions perpendicular to its propagation, so it has nowhere to expand to. A wave that is finite -- as in your drawing--- is not a ...
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### Why exactly does diffraction occur?

Your aperture only allows a very short segment of the incoming plane wave to pass through. As the aperture becomes smaller, the segment looks more and more like a point source. A point source emits ...
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### Is Huygens's Wave Theory still correct?

Huygens's Wave Theory is what you call a first order scalar diffraction theory of light. So what does it describe and what does it fail to describe? First order means that electromagnetic effects ...
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### Why exactly does diffraction occur?

A quick answer would be that they are not changing direction. Each point in the plane is the source of a single wave. Single waves expand in circles, but as you put many single waves together you ...
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### Why exactly does diffraction occur?

Tausif commented: I think OP wants to know why the diffraction occurs and why the waves don't just continue like they pointed out in the diagram. In any elastic medium, a pressure effect not only ...
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### How does Huygens Principle incorporate the unidirectional property of a traveling wave?

I'd like to add to ACuriousMind's Answer. His/Her answer emphasizes that Maxwell's equations and other equations that give rise to the Huygens spherical wave kernel in their Green's functions are ...
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### Why does the speed of light change?

The speed of light in a medium is given by $\frac{1}{\sqrt{\epsilon \mu}}$, where $\epsilon$ and $\mu$ are the relative permittivity and permeability of the medium respectively (these in turn affect ...
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### Why don't plane waves always expand according to Huygens' principle?

When you apply Huygen's principle you also have to think about all the different phases that might constructively or destructively interfere. An infinite plane wave is one example where the region of ...

### Can Schrödinger Equation be derived from Huygens' Principle?

Even mathematically, Schrödinger's equation cannot be derived from the principle of least action because it only depends on the first derivatives of time, $\psi' = \partial \psi / \partial t$. This ...
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Accepted

### Where does Huygens–Fresnel principle follow from?

The Huygens-Fresnel principle comes from looking at the Green's function for the wave equation. If we look at the response of free space to a point disturbance, it turns out to be a spherical ...
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Accepted

### Can the Huygens principle be justified rigorously mathematically?

Huygens principle is not exactly true. This is discussed in Sommerfelds 'Optics'. The problem is for example for an absorbing screen with holes the Greens function used for Huygens principle does not ...
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