- #1
Andre
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So what is it?
This is not a homework question. But I anticipate a good discussion.
This is not a homework question. But I anticipate a good discussion.
Just out of curiosity, how does "light rise up"??Originally posted by sridhar_n
(SNIP) The light from a distant object rises up, and moves from an optically denser layer to an optically lighter layer and if the angle of incidence is such that the critical angle is achieved, (SNoP)
Reflections or Refractions?
Pedants and purists insist that all mirages are purely refraction phenomena; and, strictly speaking, they are correct. Nevertheless, it is so useful to regard the classical inferior and superior mirages as approximately due to internal reflection that we cannot avoid considering that point of view — but with the caveat that certain subtle phenomena, which turn out to be essential for green flashes, are not explained by the ``reflection'' approach.
Furthermore, one should bear in mind that the words for ``mirage'' in the major languages are all derived from terms meaning ``reflection.'' I have already pointed out that the French term ``mirage'' is derived from a phrase meaning ``to be reflected.'' In German and Dutch, the terms used translate literally to ``air-reflection.'' (Luchtspiegeling -Edit) Thus the notion of reflection is implicit in every discussion of mirages. I think this close association of ``reflection'' with the classical inferior and superior mirages is a good reason to distinguish them from the ``pseudomirages,'' which are purely refractive.
Still, one can regard all these inverted images as real images (in one dimension) formed by a positive lens. From that point of view, even the classical mirages are refraction, rather than reflection, phenomena.
Originally posted by Integral
As far as I know reflection is not a carefully defined term.
Originally posted by Andre
Semantics? I don't think so. I think that sridhar_n is about right. As far as the input and output of a Mirage producing system is concerned I think it is 100% reflection and 0,0% refraction. Not even a little refraction as net result.
Why is it that none of these pages explaining mirages do not substantiate it with Snellius law? Because it doesn't work.
Originally posted by Adrian Baker
Perhaps not that relevant, but we use a nice experiment at my school to show refraction of light.
A long thin tank has extremely saturated salt solution in the bottom, to a depth of about an inch. Tap water is then slowly put on top of this (with a U shaped tube), to a depth of several inches. and allowed to stand for a few hours.
A laser beam is then placed at the side of the tank, about midway up, and if you've done it right, the beam takes a beautiful curved path, dipping down to the bottom.
Simple to do and VERY impressive.
TIR (Total internal reflection) only takes place when both of the following two conditions are met:
-a light ray is in the more dense medium and approaching the less dense medium.
-the angle of incidence for the light ray is greater than the so-called critical angle.
I do have some problems with this. Would this be the sole reason why it takes a generation before a correct paradigm shift can take place. I think that general understanding should be questioned at all times if not the Earth would still have been flat. Arent those forums to discuss those things. OK most challenges will be plain wrong. Please explain where I am wrong.then please do not continue your criticisms of the general understanding, when it is YOU who is having the trouble.
You're not totally wrong, but I think that you're not considering the appropriate situation. This business with the critical angle and total internal reflection if for a stark boundary between two distinct media. Mirages and the like are phenomena that occur in continuous media (no boundaries, but gradients). You are correct in that total internal reflection occurs when the angle of incidence is greater than the critical angle (by DEFINITION), but you are not correct to assume that the phenomenon of a mirage is a total internal reflection, as there is no distinct medium to which it is internal.Originally posted by Andre
Please explain where I am wrong.
Originally posted by Andre
Okay but that still does not legalize the refraction to exceed the critical angle.
Getting back on this
Sometimes theory may need revisiting.
What I was trying to explain is that the critical angle concept is probably not the right way to think about the situation. If you consider the light in terms of phase-fronts, then the part of the phase-front in lower index of refraction will travel faster than the part of the phase-front in the higher index of refraction. For the desert sand in the heat of the day, the air just above the surface is very hot, and the temperature decreases with height above the surface, so the index of refraction is lowest closest to the surface, BUT IT'S ALL AIR, NO BOUNDARY. There isn't a critical angle in the sense that there isn't a boundary, and therefore there is no question whether the light will remain in the medium; it will. If you want to think about the critical angle, then it IS 90 DEGREES less some MINUTE deficit. Why? Because the difference in the index of refraction from infinitesimal layer to adjacent infinitesimal layer is practically zero. That's why it is better to think of the problem in terms of gradients.Originally posted by Andre
Okay but that still does not legalize the refraction to exceed the critical angle.
A mirage is a naturally occurring optical phenomenon in which light rays are bent or distorted due to differences in air temperature and density. This creates an illusion of water or objects that are not actually there.
Refraction is the bending of light as it passes through different mediums with varying densities. This causes the light to change direction and can create distortions or illusions, such as a mirage.
Reflection occurs when light bounces off a surface, such as a mirror or water. This is due to the smoothness and flatness of the surface, which allows the light to bounce back at the same angle it hit the surface.
No, mirages are more commonly seen in desert or hot, arid regions where there is a significant difference in temperature between the ground and the air. However, they can also occur in other locations with similar atmospheric conditions.
It is not possible for objects to be completely invisible due to refraction alone. However, light refraction can create illusions and distortions that can make objects appear to be hidden or invisible from certain angles.