- #1
jackiepollock
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Why are lights reflecting off horizontal surfaces like the road, water, or snow horizontally polarized? How does the process happen?
How does polarisation in nature work?
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In summary, when light shines onto a horizontal surface, like the road, water, or snow, the waves are reflected in a horizontal polarization. This happens because the electric field is not perpendicular to the surface, and the waves are excited and reflected more easily because of this.
- #2
tech99
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The shine from water comes from electrons in the water which are vibrating in response to the electric field of the incoming light and causing re-radiation. When a vertically polarised ray of light enters water, it is bent downwards. The charges now vibrate edge-on to the viewer, and do not radiate in their direction.
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sophiecentaur
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The phenomenon of polarisation is the same over the whole electromagnetic spectrum and often it's useful to think in terms of radio waves and the way they interact. It's very complicated and not intuitive (imo) so here's a noddy explanation which has some holes in it but it carries the main message about how EM waves interact with 'substances'.
A horizontally polarised wave will excite the electrons in a long horizontal wire to oscillate and charges flow 'easily' through the wire when the E field is parallel with the wire. This will cause the wave to be (re-radiated) reflected and a 'coherent' wave front is formed from all along the wire. If the wire is not parallel to the plane of the E field, the 'component' of the E field is not parallel to the wire so less induced current will flow and the re-radiation is less. A wire at right angles to the E field will not disturb the incident wave at all because no current will flow along it. For this reason, a grid of parallel wires makes an excellent polariser for microwaves.
A metal plate conducts current so well that the induced currents can be considered to be just on the (2D) surface; it's a simpler system. Waves of any polarisation tend to be reflected well because there's an 'easy' current path across the surface. But water doesn't conduct like metal and the currents that are induced, don't just flow in the surface (not enough current) and you have to deal with a 3D situation where waves will travel through the water as well as being reflected. The angle of the E vector and the direction of the incident wave affect how much is reflected and how much is transmitted. The horizontal component reflects better than the vertical component. The proportion of reflected and transmitted energy depends on the materials involved and the angle of incidence.
PS there is a common explanation of the mechanism of selecting the polarisation of light which is referred to the 'picket fence' model. You need to read this with care, always because it ain't anything like that in most cases.
A horizontally polarised wave will excite the electrons in a long horizontal wire to oscillate and charges flow 'easily' through the wire when the E field is parallel with the wire. This will cause the wave to be (re-radiated) reflected and a 'coherent' wave front is formed from all along the wire. If the wire is not parallel to the plane of the E field, the 'component' of the E field is not parallel to the wire so less induced current will flow and the re-radiation is less. A wire at right angles to the E field will not disturb the incident wave at all because no current will flow along it. For this reason, a grid of parallel wires makes an excellent polariser for microwaves.
A metal plate conducts current so well that the induced currents can be considered to be just on the (2D) surface; it's a simpler system. Waves of any polarisation tend to be reflected well because there's an 'easy' current path across the surface. But water doesn't conduct like metal and the currents that are induced, don't just flow in the surface (not enough current) and you have to deal with a 3D situation where waves will travel through the water as well as being reflected. The angle of the E vector and the direction of the incident wave affect how much is reflected and how much is transmitted. The horizontal component reflects better than the vertical component. The proportion of reflected and transmitted energy depends on the materials involved and the angle of incidence.
PS there is a common explanation of the mechanism of selecting the polarisation of light which is referred to the 'picket fence' model. You need to read this with care, always because it ain't anything like that in most cases.
- #4
hutchphd
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Someone should say the magic words "Brewster's Angle". Here you go
https://en.wikipedia.org/wiki/Brewster's_angle
https://en.wikipedia.org/wiki/Brewster's_angle
- #5
sophiecentaur
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All good stuff. Just a problem knowing where to stop. I remember finding Brewster a big jump in understanding.hutchphd said:
1. What is polarisation in nature?
Polarisation in nature refers to the phenomenon where light waves, or other types of electromagnetic radiation, become aligned in a specific direction as they travel through a medium.
2. How does polarisation occur?
Polarisation occurs when light waves are reflected, refracted, or scattered by surfaces or particles in a medium. These interactions cause the waves to align in a specific direction, resulting in polarised light.
3. What is the importance of polarisation in nature?
Polarisation plays a crucial role in various natural processes, such as animal navigation, communication, and camouflage. It also has practical applications in technology, including 3D glasses, polarised sunglasses, and LCD screens.
4. Can polarisation be observed in other forms of energy besides light?
Yes, polarisation can also occur in other forms of electromagnetic radiation, such as radio waves and microwaves. It can also be observed in sound waves and seismic waves.
5. How is polarisation measured?
Polarisation is measured using a polarimeter, which detects the orientation of the electric field in polarised light. This measurement is typically represented by a value between 0 and 180 degrees, where 0 degrees represents horizontal polarisation and 90 degrees represents vertical polarisation.
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