Why is the sea blue and the waves white?
Everyone knows that water is colorless and transparent, but when you walk along the beach, all you can see is blue sea water and white waves. Why? In the eyes of most people, sunlight is white, but it is not. Sunlight consists of a variety of lights, including visible light and invisible infrared and ultraviolet light. If a beam of sunlight is injected into a prism, the true appearance of Lushan Mountain can be revealed: what appears before our eyes is a beautiful rainbow, from top to bottom, red, orange, yellow, green, blue, and purple. The color of visible light is determined by its wavelength. Red light has the longest wavelength and violet light has the shortest wavelength.
After sunlight passes through the prism, different colors of light are absorbed, refracted and scattered to different degrees in clean seawater. In seawater, red light with longer wavelengths has strong penetration and low refraction and scattering degrees, so it is easily absorbed by seawater; while blue light and violet light with shorter wavelengths have poor penetration and will produce stronger refraction and scattering. Although the seawater looks very uniform, there is still an uneven distribution of density, so light of different colors is scattered in the seawater. The scattered light energy is inversely proportional to the fourth power of the wavelength. Therefore, blue and violet light with shorter wavelengths are easily scattered and reach our eyes. After sunlight enters the seawater and is scattered, the red light that reaches our eyes is only about 1/12 of that of violet light. Because human eyes are not sensitive to violet light but sensitive to blue light with slightly longer wavelengths, the ocean we see appears blue or dark blue.
The situation with waves is different. The spray is mainly composed of foam and some small water droplets. The surface of the foam is a water film, and the small water droplets are like small prisms. When light shines on the waves, three things happen: First, it is reflected by the waves. The surfaces of the foam and water droplets that make up the spray have almost equal opportunities to reflect light of various colors, rather than selective reflection. Secondly, the light is scattered by bubbles and droplets of water. Compared with tiny water molecules, foams and water droplets are "large particles." When large particles scatter, the relationship between the scattered light intensity and wavelength is not obvious. It is white light on it, but it is still white light in our eyes. Third, the refraction of light by small water droplets like a prism. It seems that there will be a seven-color rainbow, but since the light will reach our eyes from different directions after being refracted by countless water droplets, the eyes receive a mixture of colorful light, so what we see is still a white spray.