67 votes

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 ...
Andrew Steane's user avatar
25 votes

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 ...
MSalters's user avatar
  • 5,574
22 votes

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 ...
Maximal Ideal's user avatar
17 votes

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 ...
Yakk's user avatar
  • 4,292
10 votes

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 ...
mike stone's user avatar
  • 53.1k
9 votes

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 ...
user45664's user avatar
  • 3,036
8 votes

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 ...
Wolpertinger's user avatar
  • 11.6k
7 votes

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 ...
JalfredP's user avatar
  • 4,739
7 votes

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 ...
HolgerFiedler's user avatar
6 votes

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 ...
Selene Routley's user avatar
6 votes

Why is Huygens' principle only valid in an odd number of spatial dimensions?

This is a more detailed version of @tparker's answer. Suppose $\phi(x,t)$ is a spherically symmetric solution to the wave equation satisfying the initial conditions $$\phi(x,0)=0$$ $${\partial \phi \...
WillO's user avatar
  • 15.1k
5 votes

How does Huygens' principle deny the possibility of diffraction?

In the original statement of the principle by Huygens (sometimes known as the Huygens principle of wave propagation), he stated that every point on the propagating wavefront serves as a secondary ...
Mostafa's user avatar
  • 3,974
5 votes

Can the Huygens principle be justified rigorously mathematically?

Consider the expression for Fresnel diffraction. The electric field is given by: $$E(\vec{r})\propto\intop_{Aperture}{}E(x',y',0)\frac{e^{ikr}}{r}dx'dy'\ $$ The integrand is composed of two parts; the ...
YoA's user avatar
  • 535
5 votes

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 ...
Allure's user avatar
  • 20.5k
5 votes

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 ...
AccidentalTaylorExpansion's user avatar
4 votes

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 ...
Luboš Motl's user avatar
4 votes
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 ...
KF Gauss's user avatar
  • 7,823
4 votes
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 ...
lalala's user avatar
  • 1,771
4 votes

Does Hyugens principle apply in three dimensions?

Yes, absolutely, in general. The Huygens' principle is an intuitive picture of the solution of the Helmholtz equation through superposition of Green's functions. The basic solution is $E(\mathbf{r})=\...
Selene Routley's user avatar
4 votes

Does Huygens Principle, by itself, explain diffraction?

In short, no. Huygens principle provided a simple qualitative explanation for evolving a given wave into its future. However, beyond that it doesn't provide a prescription for how two wavefronts may ...
lineage's user avatar
  • 2,678
4 votes

Why is the path of light not visible in vacuum?

The following may be useful to consider. It is true that Huygen's principle states that every point on a wavefront acts as a source of secondary waves which travel in all possible directions. However,...
ad2004's user avatar
  • 919
4 votes
Accepted

How does Huygens' principle work with a wave pulse?

With a compact wave pulse, Huygens’ Principle still holds, and points along the wave front acts as sources. On the advancing side of the pulse, the outgoing waves from different parts of the front ...
Buzz's user avatar
  • 16k
4 votes
Accepted

Did Huygens understand light to be a transverse wave or a longitudinal wave?

Possibly interesting quote from the "Note by the translator" section (page ix) of "Treatise On Light" by Huygens, Christiaan https://archive.org/details/treatiseonlight031310mbp/...
robphy's user avatar
  • 11.8k
4 votes

Is Huygens' Law satisfied in the following case?

If by Huygens' principle, properly modified by the obliquity factor, you mean that each point of the wavefront is a source of spherical wavelets then it is not true for a variable index material. If ...
hyportnex's user avatar
  • 18.9k
3 votes

Huygens' principle under the wind

The wind basically adds new sources for waves that also have to be considered regarding Huygens' principle. These new wave sources will look different depending on the wind you choose. Maybe you can ...
Densch's user avatar
  • 136
3 votes

Is Huygens's Wave Theory still correct?

Huygens worked with scalar, longitudinal waves. This was proved to be incorrect in 1821 by Fresnel, who showed that polarization requires transverse waves. A (relevant but incomplete) history of light ...
Arnold Neumaier's user avatar
3 votes
Accepted

Is there any limit to distance between two waves when used in Huygens principle?

I think that you have found from first principles that a hemispherical lens suffers from spherical aberration? Later Here is my attempt. It might look a mess but I think that it does illustrate the ...
Farcher's user avatar
  • 95.9k
3 votes

Why is Huygens' principle only valid in an odd number of spatial dimensions?

Huygen's principle is basically equivalent to the fact that the Green's function $G(s)$ for the wave equation only has support at $s = 0$, where $s$ in the invariant spacetime interval. In other ...
tparker's user avatar
  • 47.5k

Only top scored, non community-wiki answers of a minimum length are eligible