Selective absorption is the main reason for the appearance of color. In a certain wavelength range, if a substance absorbs the light of various wavelengths passing through it in the same amount (refers to energy) and the absorption amount is small, it is called general absorption; A substance is said to have selective absorption if it significantly absorbs light energy of a certain wavelength. When sunlight hits the sea, part of the light is reflected back and the other part is refracted into the water. The light entering the water will be absorbed by the water during its propagation. The absorption of light by water is related to the wavelength of light, that is, water has selective absorption. Water significantly absorbs light with longer wavelengths, but does not absorb light with shorter wavelengths. Red light, orange light and yellow light are all absorbed at different depths, and the temperature of seawater rises. At a certain depth, green light is also absorbed. Blue light and purple light with shorter wavelength will scatter or reflect back in all directions when encountering water molecules or other particles. Therefore, when the sea is clear and transparent, the blue light and purple light that are least absorbed by the sea are reflected and scattered into our eyes, and the sea we see appears blue.
People will naturally ask the question that violet light has the shortest wavelength and its scattering and reflection should be the strongest. Why isn't the sea purple? Experiments show that human eyes are very insensitive to purple light, so they turn a blind eye to the purple light reflected by seawater. Therefore, the sea water does not appear purple, entirely because the human eye does not truthfully reflect the situation.
"Teaching Resources" Junior Middle School Physics Volume 1
/200406/ca444660.htm
Water molecules have different scattering effects on different wavelengths of visible light (red, orange, yellow, green, cyan, blue and purple) (refers to the phenomenon that some light rays scatter away from the original direction when the light beam propagates in the medium), and the scattering effect on light with short wavelength (such as green, cyan and blue) is far stronger than that of Apollo's long light (such as red and orange). In addition, the intensity of scattering is also related to the length of optical path. When the water layer is shallow, almost all wavelengths of visible light can be transmitted, and the scattering effect is not significant. Therefore, water is colorless and transparent. When the water is deep, due to the obvious scattering effect, the water appears light blue-green, and the more air dissolved in the water, the greener it is. When the water is deep, it will appear dark blue or even black. It is for this reason that the sea is blue when it is deep.
/statics/jtzy 2003 x/TT 2004 x/czpd/jxzy/04-05 Shang/hx/3/04/kb/ 1/kzzl 4 . htm
There is a beautiful legend:
Once upon a time, there was a man who loved the sea. He goes to the seaside to see the sea every day, but the sea is still very cold for him. This man said to the sea, I treat you like this and come to see you every day, but you are always indifferent to me. Can't you show me your passion? Let your love come more violently. Hai listened to his words and asked him, can you accept my love? He replied: Yes, let your love come more violently! The sea was moved by his words. In an instant, the waves rolled and the wind was strong, and the waves came to the shore one after another. He has never seen such a sea. When the waves came to him, he turned and ran. At this time, the sea is very sad.
After this time, the sea dare not give love to others easily. After a long time, another person fell in love with the sea. Not only does he come to see the sea every day, but he also moves his family to the seaside. He wants to be with the sea all his life. The sea was finally influenced by his behavior and gave him both warm love and fierce love. He didn't run away, so they combined. But after a long time, he became a little bored. He always felt that the sea gave him either peace or rolling waves. I don't think the sea can give him any other love, so he left the sea quietly.
The sea is very sad, and these are all seen by the blue sky. He said to the sea, please don't be sad. In fact, none of them understand you. What they see is only the surface of you. In fact, the underwater world is more colorful, with colorful fish, rich mineral deposits and beautiful corals. These are all prepared by you for them, and they don't understand. Blue sky said: Only I know these things.
Later, the blue sky fell in love with the sea. After the sea and the blue sky fall in love, they can't hold hands all the time because of the distant and secular prejudice. They are far apart and miss each other. As time goes by, they miss each other more strongly. In this way, day after day, year after year, when the thoughts are unbearable, the blue sky is Lacrimosa, and the blue sky tears drop into the heart of the sea. I don't know how many tears are left, and the whole sea water is dyed blue. They are all tears in the blue sky, so the sea and the sky are the same.
/printpage.asp？ BoardID = 3 & ampID=7900
The color of seawater seen by human eyes is the color of seawater reflecting light from the sun. When white light shines into seawater, seawater appears blue because of its selective absorption and scattering. When light passes through the medium, part of the energy of light is absorbed by the medium and converted into the internal energy of the medium, so that the intensity of light decreases with the thickness of the medium, which is called light absorption. If a medium absorbs light in a certain wavelength range to a small extent and does not change much with the wavelength, this absorption is called generalized absorption; If a medium absorbs some wavelengths of light very strongly and varies greatly with the wavelength, this absorption is called selective absorption. When sunlight shines on seawater, seawater selectively absorbs red and yellow light, but strongly scatters and reflects blue and purple light, so seawater looks blue. The color of most objects is the result of selective absorption of visible light on the surface or in the body.
/question/q60.htm
The color of seawater is mainly caused by the optical properties of seawater, that is, the absorption, reflection and scattering of solar rays by seawater. We know that sunlight is composed of seven colors: red, orange, yellow, green, cyan, blue and purple. The wavelengths of seven colors are different. From red to purple, the wavelengths are getting shorter and shorter. Among them, red light, orange light and yellow light with longer wavelength have stronger penetration ability and are most easily absorbed by water molecules. Blue light and purple light with short wavelength have weak penetration ability, and are most easily scattered and reflected when encountering pure seawater. Because people's eyes are not sensitive to purple light, they often turn a blind eye and are sensitive to blue light. Therefore, the ocean we see is blue or dark blue. If you put a bucket of seawater in a bowl, the seawater is as colorless and transparent as ordinary water. In fact, the sea looks not all blue, but red, yellow, white, black and so on, colorful. Because the color of seawater is not only affected by the above factors, but also by suspended solids, seawater depth, clouds and other factors. The Yellow Sea in China, for example, looks yellow-green, because a lot of sediment carried by the ancient Yellow River "polluted" the seawater. Although the Yellow River is diverted to the Bohai Sea, there is a wide Bohai Strait in the northern part of the Yellow Sea and rivers such as the Huaihe River inject it, so the sea surface is still pale yellow.
In the Red Sea between Asia and Africa, because of the high water temperature, an algae grows in the sea, which turns reddish brown after a large number of deaths and dyes the seawater red. The Red Sea got its name from this.
In the Black Sea, due to the injection of rivers such as Danube River, Don River and Dnieper River, the surface density is very low, and the deep layer is influenced by the high salinity seawater in the Mediterranean, so the density is very high. In this way, the upper density is small, the lower density is large, and the difference is large, so it is difficult to exchange the upper and lower water bodies. There is only a narrow and shallow Turkish Strait between the Black Sea and the Mediterranean Sea, which makes it difficult to exchange a lot of seawater between them. In this way, the lower seawater of the Black Sea has been in an anoxic environment for a long time, and the sewage secreted by creatures and various animals and plants in the upper seawater sinks into the depths to rot and stink after death, and a large amount of sludge turns the seawater black.
The Arctic Ocean goes deep into the White Sea in northern Russia. Because of its high latitude, cold all year round, boundless ice and snow and low organic matter content, the seawater is white, hence the name "White Sea".
http://www . nhyz . org/yxx/jxzy/gzdlzy/dqs dx/dqs dx _ 15 . htm