diffraction
dif·frac·tion
D0217100 (dĭ-frăk′shən)diffraction
(dɪˈfrækʃən)dif•frac•tion
(dɪˈfræk ʃən)n.
dif·frac·tion
(dĭ-frăk′shən)diffraction
Noun | 1. | ![]() |
单词 | diffraction | |||
释义 | diffractiondif·frac·tionD0217100 (dĭ-frăk′shən)diffraction(dɪˈfrækʃən)dif•frac•tion(dɪˈfræk ʃən)n. dif·frac·tion(dĭ-frăk′shən)diffraction
diffractiondiffraction,bending of waves around the edge of an obstacle. When light strikes an opaque body, for instance, a shadow forms on the side of the body that is shielded from the light source. Ordinarily light travels in straight lines through a uniform, transparent medium, but those light waves that just pass the edges of the opaque body are bent, or deflected. This diffraction produces a fuzzy border region between the shadow area and the lighted area. Upon close examination it can be seen that this border region is actually a series of alternate dark and light lines extending both slightly into the shadow area and slightly into the lighted area. If the observer looks for these patterns, he will find that they are not always sharp. However a sharp pattern can be produced if a single, distant light source, or a point light source, is used to cast a shadow behind an opaque body. Diffraction also occurs when light waves interact with a device called a diffraction grating. A diffraction grating may be either a transmission grating (a plate pierced with small, parallel, evenly spaced slits through which light passes) or a reflection grating (a plate of metal or glass that reflects light from polished strips between parallel lines ruled on its surface). In the case of a reflection grating, the smooth surfaces between the lines act as narrow slits. The number of these slits or lines is often 12,000 or more to the centimeter (30,000 to the inch). The ruling is generally done with a fine diamond point. Since the light diffracted is also dispersed (see spectrumspectrum,arrangement or display of light or other form of radiation separated according to wavelength, frequency, energy, or some other property. Beams of charged particles can be separated into a spectrum according to mass in a mass spectrometer (see mass spectrograph). ..... Click the link for more information. ), these gratings are utilized in diffraction spectroscopesspectroscope, optical instrument for producing spectral lines and measuring their wavelengths and intensities, used in spectral analysis (see spectrum). When a material is heated to incandescence it emits light that is characteristic of the atomic makeup of the material. ..... Click the link for more information. for producing and analyzing spectra and for measuring directly the wavelengths of lines appearing in certain spectra. The diffraction of X rays by crystals is used to examine the atomic and molecular structure of these crystals. Beams of particles can also exhibit diffraction since, according to the quantum theoryquantum theory, modern physical theory concerned with the emission and absorption of energy by matter and with the motion of material particles; the quantum theory and the theory of relativity together form the theoretical basis of modern physics. ..... Click the link for more information. , a moving particle also has certain wavelike properties. Both electron diffraction and neutron diffraction have been important in modern physics research. Sound waves and water waves also undergo diffraction. DiffractionThe bending of light, or other waves, into the region of the geometrical shadow of an obstacle. More exactly, diffraction refers to any redistribution in space of the intensity of waves that results from the presence of an object that causes variations of either the amplitude or phase of the waves. Most diffraction gratings cause a periodic modulation of the phase across the wavefront rather than a modulation of the amplitude. Although diffraction is an effect exhibited by all types of wave motion, this article will deal only with electromagnetic waves, especially those of visible light. For discussion of the phenomenon as encountered in other types of waves See Electron diffraction, Neutron diffraction, Sound Diffraction is a phenomenon of all electromagnetic radiation, including radio waves; microwaves; infrared, visible, and ultraviolet light; and x-rays. The effects for light are important in connection with the resolving power of optical instruments. See X-ray diffraction There are two main classes of diffraction, which are known as Fraunhofer diffraction and Fresnel diffraction. The former concerns beams of parallel light, and is distinguished by the simplicity of the mathematical treatment required and also by its practical importance. The latter class includes the effects in divergent light, and is the simplest to observe experimentally. To illustrate the difference between the methods of observation of the two types of diffraction, Fig. 1 shows the experimental arrangements required to observe them for a circular hole in a screen S. The light originates at a very small source O, which can conveniently be a pinhole illuminated by sunlight. In Fraunhofer diffraction, the source lies at the principal focus of a lens L1 which renders the light parallel as it falls on the aperture. A second lens L2 focuses parallel diffracted beams on the observing screen F, situated in the principal focal plane of L2. In Fresnel diffraction, no lenses intervene. The diffraction effects occur chiefly near the borders of the geometrical shadow, indicated by the broken lines. An alternative way of distinguishing the two classes, therefore, is to say that Fraunhofer diffraction concerns the effects near the focal point of a lens or mirror, while Fresnel diffraction concerns those effects near the edges of shadows. Photographs of diffraction patterns are shown in Fig. 2. diffraction(di-frak -shŏn) The bending of light or other electromagnetic radiation at the edges of obstacles, with the resulting formation of light and dark bands or rings (diffraction patterns) at the edges of the shadow. An example of a diffraction pattern is the Airy disk observed in telescope images of distant celestial objects. A small aperture or slit produces similar annular or banded patterns. Diffraction results from the wave nature of electromagnetic radiation. See also interference.
diffraction[di′frak·shən]diffractiondiffractionThe bending of electromagnetic waves as they pass around corners or through holes smaller than the wavelengths of the waves themselves. See diffraction grating and refraction.diffractiondiffraction[dĭ-frak´shun]dif·frac·tion(di-frak'shŭn),dif·frac·tion(di-frak'shŭn)diffractiondiffraction
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