Xiang Yangyang, science teacher at Jingyuan Middle School, Qiantang District, Hangzhou City
In summer, it is easy for us to see a seven-color rainbow appearing in the sky after a rain. Many passers-by will take this opportunity to take pictures of this beautiful natural landscape with their mobile phones and send it to their WeChat Moments to express their praise for the gifts of nature. So do you know the cause of the rainbow and the origin of its colors?
Causes of rainbows
Rainbows most often appear when the sky turns sunny just after a rain. At this time, the air is less dusty and full of small water droplets. One side of the sky is darker because there are still rain clouds, but there are no more above or behind the observer. Clouds block the sunlight, making the rainbow easier to see.
Sunlight is actually a kind of composite light, including visible light and invisible light. Invisible light mainly refers to infrared and ultraviolet light, and the rainbow we see is actually caused by visible light shining on small, nearly spherical water droplets in the air, causing refraction and reflection. The specific process is as follows:
sunlight strikes the surface of a water droplet and is refracted once
. The visible light in sunlight is white light, which is composed of different monochromatic lights . Spherical water droplets have a dispersive effect on light. Different monochromatic lights have different refractive indexes due to different frequencies and wavelengths. The refractive index of red light is smaller than that of blue-violet light, causing the deflection angle of blue-violet light to be larger than that of red light. Therefore, the composite white light turns into different monochromatic lights after the first refraction, forming what we often call the seven color bands - red, orange, yellow, green, blue, indigo and violet.
In fact, humans have been able to disperse white light through prism for a long time, but it was Newton who first designed the relevant prism experiment and passed the typical scientific law of "experimental induction-hypothesis theory-experimental test" The research method is permeated with analysis (decomposing white light into monochromatic light for research) and comprehensive methods (compositing monochromatic light into white light).
The refracted light of different colors is reflected on the back of the water drop.
The light will be reflected again in the water droplet after the first refraction, so the spectrum seen by the observer will be exactly opposite to the spectral distribution produced after the first refraction. . When
finally leaves the water droplet, it is refracted again
. After the second refraction, the colored light enters the human eye, and finally forms vision in the human cerebral cortex, that is, the different colors of light we see. (For example, the wavelength of light that causes the brain to produce "red" vision is about 620-760nm, and the wavelength of light that produces "green" is about 520-560nm)
The color of objects
With the continuous deepening of the study of spectrum and color, we found that : Everything in the world is colorful mainly because the sunlight shines on the surface of objects, and the colored light reflected into our eyes determines the color of the objects. For example, when we observe leaves, it is because the green light that hits the leaves is reflected by the leaves, while other colors of light are absorbed, causing the leaves we see to be green. What is relatively special about
is that when an object can absorb all colored lights, our brain cannot receive any visible light and recognize it as "black". Just like when we observe leaves at night without lights, because there is no light at this time, no light is reflected to our eyes, and what we see becomes pitch black. And when an object cannot absorb any color light and reflects all color light, we will recognize it as "white".
With the deepening of research, we found that there are three basic colors in color that can no longer be decomposed, namely the three primary colors of and (red, green and blue) that we now mention. Adding the three primary colors in different proportions can produce a variety of colors.
Extended thinking questions:
Why is there no brown in the visible light spectrum?
In fact, "brown" does not exist at all! Brown is just a color recognized by the human brain, and its formation is also related to its background color. In fact, brown itself is actually a darker "orange" and appears "dark orange" in an environment with a dark background. However, in an environment with a white background, our brains mistakenly recognize it as a new color. --"brown".
Why do the three primary colors in art refer to red, yellow and blue, not red, green and blue?
The three primary colors of light belong to the research category of physics. They are obtained by physicists based on the dispersion theory and experiments of light. The mixing of the three optical primary colors belongs to additive color development. The light will become brighter as the light is added. Mixing two or two can produce a brighter intermediate color. For example, if red and green are mixed to form yellow, yellow is the complementary color of blue because it does not contain blue at all. Two complementary colors mixed in equal amounts also form white. After the two colors of light are mixed, the light is enhanced and the brightness is higher than the initial brightness of the two colors of light. In addition, the more combined colors there are, the more light there is and the closer the color is to white.
The three primary colors of pigments discussed in art are the research system of colorists. Their research shows that the three primary colors of pigments are red, yellow, and blue. The mixing of pigment colors belongs to subtractive color development. The pigment itself cannot emit light and must rely on white light to produce reflection so that it can be seen by the eyes. For example, if you mix yellow pigment and blue pigment, because the yellow pigment absorbs blue light and the blue pigment absorbs red light, only green light is reflected. This is the reason why yellow pigment plus blue pigment form green. When two colors of paint are mixed, their luminosity will be lower than the original luminosity of the two colors. In addition, the more combined colors, the more light will be absorbed, and the closer the color will be to black.
Why do the iron blocks we usually see are white, while iron powder is black?
For iron blocks and iron sheets, when light shines on them, the surface forms a specular reflection, so a lot of visible light is reflected into the eyes, forming white color. The surface area of iron powder is small and there is no fixed geometric shape. Therefore, when light hits the surface of iron powder, it forms diffuse reflection, and not much visible light can be reflected into the eyes, so it appears black.
This article is an original work of Qianjiang Evening News. Without permission, any use of the copyright of the work, such as reprinting, copying, excerpting, adapting and disseminating on the Internet, is prohibited. Otherwise, this newspaper will pursue the legal liability of the infringer through judicial channels.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-