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Seminar - Guyton e Hall - Fisiologia medica 13 ed.
Biology
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Phenomena of Light in Nature: An Overview The interaction of light with objects around us creates several spectacular natural phenomena. Some of these include the blue color of the sky, the color of water in the deep sea, and the reddening of the sun at sunrise and sunset. These effects are due to the scattering of light by particles in the atmosphere.
Scattering of Light by Colloidal Particles In our previous class, we discussed the scattering of light by colloidal particles. When a beam of light passes through a true solution, its path is not visible. However, when it passes through a colloidal solution, where the particles are relatively larger, the path becomes visible. This visibility is due to the scattering of light by the colloidal particles.
Tyndall Effect The Tyndall effect is a phenomenon where light is scattered by particles in a colloidal solution, making the path of the light beam visible. The Earth’s atmosphere, a heterogeneous mixture of minute particles like smoke, water droplets, dust, and air molecules, demonstrates this effect. When a beam of light strikes these particles, it gets diffusely reflected, making the beam’s path visible.
This effect can be observed when a beam of sunlight enters a smoke-filled room or when sunlight passes through the canopy of a dense forest. In both cases, the scattering particles, such as smoke or water droplets, make the light path visible.
The color of the scattered light depends on the size of the scattering particles. Very fine particles scatter mainly blue light, while larger particles scatter light of longer wavelengths. If the scattering particles are large enough, the scattered light may even appear white.
Why is the Sky Blue? The blue color of the clear sky is due to the scattering of sunlight by the molecules of air and other fine particles in the atmosphere, which are smaller than the wavelength of visible light. These particles scatter light of shorter wavelengths (blue light) more effectively than light of longer wavelengths (red light). Red light has a wavelength about 1 times greater than blue light.
As sunlight passes through the atmosphere, the fine particles scatter blue light more strongly than red light. The scattered blue light enters our eyes, making the sky appear blue. If Earth had no atmosphere, there would be no scattering, and the sky would look dark, as it does to passengers flying at very high altitudes where scattering is minimal.
Red Danger Signal Lights You may have noticed that danger signal lights are red. This is because red light is scattered the least by fog or smoke, making it visible from a distance in the same color. This property makes red light an effective choice for warning signals.
In summary, the interplay of light with particles in the atmosphere gives rise to various natural phenomena, with scattering playing a significant role in the visibility and color of these effects. The Tyndall effect, the blue color of the sky, and the use of red in danger signals all exemplify the fascinating ways light interacts with our environment.
Seminar - Guyton e Hall - Fisiologia medica 13 ed.
Subject: Biology
