When the diffracting object is repeated, the effect is to narrow each maximum, concentrating its energy within a narrower range of angles.The diffraction angles are invariant under scaling that is, they depend only on the ratio of the wavelength to a dimension, a, of the diffracting object.(More precisely, this is true of the sines of the angles.) When the dimensions of the diffracting object are reduced, the angular spacing of the diffraction pattern is increased in inverse proportion.Several qualitative observations can be made: Historically, the first proof that light was a wave phenomenon came from the double-slit experiment of Thomas Young. The destructive-interference locations are the minima. The constructive-interference locations are called maxima, because they have maximum brightness. The second figure shows the result of this process with light waves of a single wavelength originating from a laser. However, when a trough and a crest overlap, they cancel out the interference is destructive. Constructive interference also occurs where a trough overlaps another trough. Where a crest overlaps with a crest, a double-height crest will be formed this is constructive interference. After passing through the slits, two overlapping patterns of semicircular ripples are formed, as shown in the first figure. Suppose, for the sake of visualization, that these are water waves. The most conceptually simple example of diffraction is double-slit diffraction in which both slits have relatively narrow widths compared to the wavelength of the wave. See electron diffraction and neutron diffraction. As the wavelengths of these particle-waves are so small they can be used as probes of the atomic structure of crystals. It is possible, due to wave-particle duality, to observe diffraction of particles such as neutrons or electrons. It is the diffraction of "particles," such as electrons, which stood as one of the powerful arguments in favor of quantum mechanics. Refraction is not an interference phenomenon, and, e.g., can occur without coherence. In well-defined cases, a diffraction pattern may be observed.ĭiffraction is not the same as refraction, although both are phenomena in which a wave does not propagate in a single direction. Diffraction will not occur if the wave is not coherent, and diffraction effects become weaker (and ultimately undetectable) as the size of obstruction is made larger and larger compared to the wavelength. Not all interference is diffraction for example, sound waves emitted by two stereo speakers will interfere with each other if they are of the same frequency and have a definite phase relationship, but this is not diffraction. As a simple example of diffraction, if you speak into one end of a cardboard tube, the sound waves emerging from the other end spread out in all directions, rather than propagating in a straight line like a stream of water from a garden hose.ĭiffraction is one particular type of wave interference, caused by the partial obstruction or lateral restriction of a wave. Diffraction also occurs when any group of waves of a finite size is propagating for example, a narrow beam of light waves from a laser must, because of diffraction of the beam, eventually diverge into a wider beam at a sufficient distance from the laser. It can occur with any type of wave, including sound waves, water waves, and electromagnetic waves such as light and radio waves. Diffraction is the apparent bending and spreading of waves when they meet an obstruction.
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