Poisson/Arago's spot in water?

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In summary, Poisson's spot is an effect of light caused by its wave nature, where a bright point appears in the center of the shadow of a round object. The question was posed whether Arago's spot, a similar phenomenon, can also be observed in water waves, taking into account their differences from electromagnetic waves. While it seems possible in theory, further research is needed, making it an interesting undergraduate project. The 2D equivalent of Arago's spot would be similar to an inverted single slit experiment and should be observable.
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nonequilibrium
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Hello,

So Poisson's spot is a (peculiar) effect of light due to its wave nature (it's the bright point one would see in the middle of the shadow of a perfectly round coin).

So I was wondering, has Arago's spot been observed for water waves too? For example in a 2D equivalent, i.e. for surface gravity waves.
 
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Interesting... it seems that there could be, but water waves are slightly different than electromagnetic waves- the dispersion relation for example, and dissipation due to viscosity. Lamb only treats sound waves diffracted though a aperture that is smaller than the wavelength, and those results do not indicate any phenomenon similar to the spot of Arago.

Seems like a good undergraduate project, actually!
 
  • #3
The 2D equivalent would be like an inverted single slit experiment - should be observable.
 

Related to Poisson/Arago's spot in water?

1. What is Poisson/Arago's spot in water?

Poisson/Arago's spot is a phenomenon in which a bright spot is seen in the center of a circular shadow when a small object is placed in a pool of water in a well-lit area. It was first observed by French physicist Siméon Denis Poisson and later studied by French scientist François Arago in the early 19th century.

2. What causes the Poisson/Arago's spot?

The Poisson/Arago's spot is caused by the diffraction of light waves around the edges of the object which interfere with each other, creating a bright spot in the center of the shadow. This is due to the wave nature of light.

3. Can the Poisson/Arago's spot be observed with any object?

No, the Poisson/Arago's spot can only be observed with small, round objects that have a diameter that is comparable to the wavelength of light, which is approximately 500 nanometers.

4. How is the Poisson/Arago's spot related to the size of the object and the distance from the water's surface?

The size of the spot and the distance from the water's surface are directly proportional. This means that as the size of the object or the distance from the water's surface increases, the size of the spot also increases.

5. What is the significance of the Poisson/Arago's spot?

The Poisson/Arago's spot is significant because it provides evidence for the wave nature of light, which was a topic of debate in the early 19th century. It also has practical applications in various fields, such as microscopy and astronomy, where it can be used to improve the resolution of images.

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