Diffused reflection definition8/26/2023 These three types of diffusion correspond to different modes of interaction of light with the diffusing object. The central spot has the largest width L= 2Dθ, where the small angle θ is λ/a. The diffraction of a red light through a thin slit leads to a pattern of red spots separated by dark areas. Thus, this colour is typical of the blue line of the Vosges above coniferous forests emitting pollen and isoprene microbeads (originally a compound of natural rubber).įigure 2. On the other hand, at intermediate scales, close to the wavelengths of light, such as pollens, aerosols and fumes, Mie scattering imposes a slightly bluish greyish grey colour. It is therefore no longer selective, which explains the white colour of the clouds, with shades of grey depending on the amount of sunlight absorbed. Diffusion is then reduced to multiple reflections on the droplet surface. Water droplets suspended in clouds and fogs can reach 100 microns, much larger than the wavelength of light. At the scales of air molecules, or water molecules constituting ice, objects much smaller (nanometers) than the wavelengths of light (between 0.4 and 0.8 μm), scattering is predominant for short wavelengths, thus selecting the color blue. Bluish colours in an ice cave due to Rayleigh scattering. The diffusion of light depends on the size of the diffusing objects, read The colours of the sky.įigure 1. In English, the distinction between this phenomenon and molecular diffusion is clear since this phenomenon is called scattering. On the other hand, in a transparent medium, such as air or ice, whose composition is not uniform, diffusion may occur. It is then not subject to any distribution. On the contrary, light can propagate in a vacuum. SOMMERIA Jöel, Joël Sommeria Author Encyclopedia Environment Research Director at the CNRS, Laboratory of Geophysical and Industrial Flows (LEGI).įor quantities such as the mass of a contaminant, heat or the amount of movement, the existence of a stirring material at microscopic scales is necessary for their diffusion. ![]() Each individual reflection still obeys the law of reflection, but the different parts of the rough surface are at different angles.MOREAU René, Professor Emeritus in Grenoble-INP, SIMaP Laboratory (Science and Engineering of Materials and Processes), member of the Academy of Sciences and the Academy of Technologies. This may cause a distorted image of the object, as occurs with rippling water, or no image at all. Instead of forming an image, the reflected light is scattered in all directions. If a surface is rough, diffuse reflection happens. ![]() A ray diagram showing how an image forms in a plane mirror Diffuse reflection ![]() In a virtual image, the rays appear to diverge from behind the mirror, so the image appears to come from behind the mirror. ![]() This is the type of reflection that happens with a flat mirror. Reflection from a smooth, flat surface is called specular reflection. The diagrams show a water wave being reflected at a barrier, and a light ray being reflected at a plane mirror. The angles of incidence and reflection are measured between the light ray and the normal - an imaginary line at 90° to the surface. The reflection of sound causes echoes.įor example, if a light ray hits a surface at 32°, it will be reflected at 32°. Waves - including sound and light - can be reflected at the boundary between two different materials.
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