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lots of very complex answers The simple answer is this. A wave is a distribution of pressure caused by things being closer together than their natural . This could be interpreted as therefor having a higher energy or entropy which they seek to shed. As such this happens in all directions ... so a point wave will dissipate in a spherical fashion. A moving ...

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The wave propagates in the direction perpendicular to the surface of the wave front. The bit of the wave front that passes through the hole now has a surface on all sides, so it propagates in all directions. Why does the wave propagate perpendicular to the wave front? Because waves are caused by restoring forces that smooth out differences - if you pull a ...

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I'll take a stab at a less scientific or mathematical approach to the problem. You can think of water molecules as wanting to make the surface of the water as flat as possible. Seeing as any body of water will eventually become still (flat surface) if no outside forces work on it, it makes sense intuitively. Of course water molecules can only feel the ...

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As Chris Mueller pointed out, plane waves can simply be regarded as caused by a given distribution of point sources. As to why point sources should form spherical waves, you can maybe think of it as a consequence of the definition itself of a "point source". Indeed, when you say "point source" you are implicitly defining an object which has no privileged ...

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The best intuition is the well-defined mathematics underlying the concept. The simplest equation for the wave is $$\frac{\partial^2}{\partial t^2} h = c^2 \frac{\partial^2}{\partial x^2} h + c^2\frac{\partial^2}{\partial y^2} h$$ Here, $c$ is the speed of the waves ("fundamental" physicists would think about the speed of light as the most well-known example ...

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I think you are looking at the question in a slightly backwards way. It would be better phrased as: Why is it possible to have plane waves? In physics all point sources, wave sources which are smaller than the wavelength, generate outgoing spherical waves. As an example consider throwing a rock into a pond; the outgoing waves are emitted equally in all ...

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If the slit width is large compared to the electron wavelength then the spot size will be the same as the slit width (assuming the electron beam doesn't diverge): $$\text{spot size} = w$$ In the limit of small slit width you get the equation you cite for the (half) angular divergence, and the spot width will be (assuming $\sin\theta \approx \theta$):  ...

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I think you have invented the zone plate, a kind of specialized flat circular diffraction grating that acts as a lens. It consists of a set of concentric transparent zones of decreasing widths. The width you have derived is the diameter of the first zone. Subsequent zones interfere constructively by allowing paths differing by integer multiples of the ...

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