So I’m at the Red Lobster the other day, looking into the Lobster tank, when I remember that I’ve always wondered why the inside of the glass appears as a mirror. Now I have a little understanding of light-physics and refraction densities, but what is light doing in there to cause this phenomenon? I know if I were to dip my head in the tank I would see through, and in that respect, I can look through from one side to the other, but if I’m on an angle: Perfect Mirror. Hmmph?
The phenomenon is known as total internal reflection; a google search on those three words turned up a whole load of hits, all of which looked pretty good, so d’ya mind if I don’t bother posting any of them here?
I believe it’s the same sort of thing that causes hot roads to look like they have puddles on them (something to do with boundaries between materials of different refractive indexes).
Yes, it has to do with total internal reflection. I just did a quick experiment where I turned on my fish tank lights (waking up the fish) and tried to see my hand on the side of the tank by looking through the front. You can do it if you look at a high enough angle with respect to the side ie; plaster your cheek against the front and you can just see your hand on the side. I make aquariums, and this is what can make odd-shaped (not rectangular) tanks look cool or confusing when filled. It can also make tank look larger inside by reflecting back some of the internal areas.
Another thing about this; this effect is exactly what makes optical fibres work so well; the light travelling along inside the fibre never strikes the internal surface at a steep enough angle to exit the medium, so the only loss is through absorption (which is minimal due to the purity of fibre optic glass)
Total Internal Reflecion occurs when the sine of the angle of incience equals or exceeds 1/(index of refrction) = 1/1.333 for water at the sodium D line.
A really good illustration of this can be seen in you go down to the bttom o a swiming pool with a really flat surface and look up. You’ll see a sort of Fish-Eye view of the surface world in the center, but beyond a certain range you get a mirror reflection of the bottom.