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J. Perelman
"Entertaining physics". Book 2.
Chapter 9. Reflection and refraction of light. Vision

WORLD UNDER WATER

Many people don't know how extraordinary would seem the world, if we were to consider it from under the water: it must be submitted to the observer changed and distorted almost beyond recognition.

Imagine that you are immersed in the water and watch from under the water table in the world surface. The cloud hanging in the sky right above your head, did not change his view: vertical beam is not refracted. But all other items, the rays which meet the water surface at an acute angle, appear distorted: they seemed to shrink in height - the stronger, the more acute the angle between the beam with the surface of the water. It is clear: the whole world, visible above the water, must fit in close underwater cone; 180 degrees should be compressed almost doubled to 97, and the image will inevitably be distorted. Subjects rays which meet the water surface at an angle of 10 degrees, is compressed in the water so that almost cease to differ. But just more impressed if you view the water surface from under the water she is not flat, and the cone shape! You feel that you are at the bottom of a huge crater, the sides of which are inclined to each other at an angle a little more direct (97 degrees). The top edge of the cone is surrounded by a rainbow ring of red, yellow, green, blue and purple edges. Why? White solar light consists of a mixture of rays of different colors; each genus of rays has its own refractive index, and therefore its "critical angle". The consequence of this is that when viewed from the water, the subject seems to be surrounded by colorful halo of rainbow colors.

What is seen beyond the edges of the cone that encompasses the entire surface world? There is a scene of glittering surface of the water, in which, as in a mirror, reflected underwater objects.

Quite an unusual appearance for underwater observer those items that are part of the submerged part of the same act over it. Let the river submerged water rail (Fig. 1). That will see the observer, placed under water, at point a?


Figure 1. View emergent water Reiki for underwater observer whose eyes are placed in A.
In the corner 2 is visible in the hazy outlines of the immersed part of Reiki. In the corner 3 - its reflection from the inner surface of the water. Still visible above the protruding portion of the rail in the reduction, and, moreover, separated from the rest of the period. In the corner 4 shows the bottom. In the corner 5 entire visible surface of the world in the form of a conical tube. In the corner 6 shows the reflection of the bottom from the bottom surface of the water. In the corner of 1 - dim image of the bottom.

Divide the monitored space to them - 360 degrees - at the plots will look at each section separately. Within an angle 1 he will see the bottom of the river, unless, of course, it is well lit. In the corner 2 he will see the underwater part of the Reiki without distortion. Around the corner 3, he will see the reflection of the same part, Reiki, i.e. inverted submerged half of it (remember what was said about "total internal reflection"), Even higher underwater observer will see the protruding portion of the rail, but she will not continue underwater, and will move much higher, completely separated from its Foundation. Of course, the observer will not think that this floating rake is a continuation of the first! In addition, the rake will seem strongly compressed, especially in the lower part, where the division will be noticeably close. The tree on the Bank, flooded by the spill, should from under the water to look the way it is depicted in Fig. 2.


Figure 2. As appears from under the water a half-tree (cf. with Fig. 1).

And if Reiki were people, from under the water he would figure Fig. 3. In this form the bather must appear to the fish! For them we are going on a shallow bottom, split into two beings: the upper legs, the lower - headless with four legs! When we are removed from the underwater observer, the upper half of our body is increasingly compressed in the lower part; at a distance almost all surface torso disappears, only one freely blowing head...


Figure 3. As bather, submerged up to his chest in water, it is an underwater observer (cf. with Fig. 2).

Can I directly experience, check out these extraordinary conclusions? Ducking under the water, we would have seen very little, even if I trained myself to keep my eyes open. First, water does not have time to calm down in those few seconds, what we are able to spend under water, and through the undulating surface is difficult to distinguish anything. Secondly, as we have explained previously, the refraction of the water is not very different from the refractive index of the transparent media of our eye, and the retina is therefore very unclear image; surroundings will seem vague and blurred. Observation of the diving bell helmet or through a glass window of a submarine also could not give the desired results. In these cases, as we have already explained, the observer though it is under water, but not in terms of "underwater view": before engaging in his eyes, the light rays in these cases, passing the glass, re-entering, into the air and, therefore, feels the opposite refraction; or recover the same direction of the beam, or he gets a new direction, but at least not the one that was in the water. This is why observations from the glass Windows of the submarine areas may not give a correct view about the conditions of the underwater view."

Entertaining physics J. Perelman

 




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