Construct · 4 fields · 4 citations
One name. Different field. Different construct. One map.
● jingle · one word, four kinds of wave spreading Nearest construct by meaningBragg's lawcompare the meaningsEvery construct on the map is compared with every other by the meaning of its definitions, and the closest one is surfaced here. The nearest construct to diffraction is Bragg's law.
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Diffraction is the spreading and bending of a wave as it passes the edge of an obstacle or goes through an opening, so the wave reaches places that a straight ray would leave in shadow. When light passes through a narrow slit it fans out, and light through two slits builds a pattern of bright and dark bands, because the spreading waves overlap and either add or cancel. The same effect sets the diffraction limit, the smallest detail an optical instrument can resolve, since a lens of finite width gathers only part of the spreading wavefront. Born and Wolf's Principles of Optics treats diffraction as a consequence of the wave nature of light and works out these patterns from how a wavefront propagates past an aperture. The referent is the spreading of a wave through an opening or past an edge, set by the wavelength and the size of the aperture, and it is not a probe of crystal structure, sound bending around a wall, or a beam of electrons.[1]
In x-ray crystallography, diffraction is the scattering of X-rays off the regularly spaced atoms of a crystal, which reinforces the scattered waves only in certain directions and so encodes the arrangement of the atoms. Because the spacing between planes of atoms is close to the wavelength of X-rays, a crystal acts as a three-dimensional grating, and the sharp spots it produces follow Bragg's law, which links the angle of each spot to the spacing of the planes and the wavelength. Bragg and Bragg's The reflection of X-rays by crystals set out this relation and used it to read the spacings inside real crystals. From the positions and brightnesses of the diffracted spots, the electron density and the atomic structure can be reconstructed, which is how the structures of DNA and countless proteins were solved. The referent is the ordered scattering of X-rays by a crystal lattice, recorded as a pattern of spots and used to determine atomic structure, not the general spreading of a wave through a slit, sound around a barrier, or electron waves in a beam.[2]
Diffraction of sound is the bending of sound waves around the edge of a barrier or through a gap, which is why you can hear someone talking around a corner or on the far side of a wall. Because audible sound has wavelengths from centimetres to metres, comparable to the size of everyday obstacles, it bends around them far more readily than light does. This bending sets how well a noise barrier along a road or railway actually shields the area behind it, since sound diffracts over the top edge and fills in part of the shadow. Maekawa's Noise reduction by screens measured how much a screen cuts sound as a function of its size and the wavelength, and gave a widely used way to predict the attenuation behind a barrier. The referent is the bending of sound around obstacles and through openings, measured as the sound level left in the shadow of a barrier, and it is distinct from light through a slit, X-rays off a lattice, or electron waves.[3]
In quantum physics, diffraction is the spreading and interference of matter waves, the wave-like behaviour that particles such as electrons show when they scatter off a regular array of atoms. A beam of electrons aimed at a crystal does not simply bounce off in one direction but comes back strongest at particular angles, exactly as a wave through a grating would, which was direct evidence that particles have a wavelength. Davisson and Germer's Diffraction of electrons by a crystal of nickel reported these angle-dependent peaks and matched them to the wavelength that de Broglie had predicted from the electrons' momentum. The effect confirmed wave-particle duality and is now the basis of electron diffraction methods for studying surfaces and materials. The referent is the wave behaviour of massive particles scattering off a crystal, measured as peaks in scattered intensity at particular angles, and it is a different object from a light wave, an X-ray pattern, or a sound wave, even though all four are named diffraction.[4]
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