B How does polarisation in nature work?

[jackiepollock]

Why are lights reflecting off horizontal surfaces like the road, water, or snow horizontally polarized? How does the process happen?

 

[tech99]

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.

 

[sophiecentaur]

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.

 

[hutchphd]

Someone should say the magic words "Brewster's Angle". Here you go

https://en.wikipedia.org/wiki/Brewster's_angle

 

[sophiecentaur]

Someone should say the magic words "Brewster's Angle". Here you go

https://en.wikipedia.org/wiki/Brewster's_angle

All good stuff. Just a problem knowing where to stop. I remember finding Brewster a big jump in understanding.