X-rays are electromagnetic waves of very short wavelengths ( of the order of 0.1 nm). of the order of wavelength λ of the wave, is available. The wavelength of an electromagnetic wave can be determined if a grating of the proper spacing i.e. A narrow slit, therefore, produces a series of bright and dark regions with the first bright region at the centre of the pattern. The region between any two consecutive minima both above and below O will be bright. In general, the conditions for different orders of minima on either side of the centre are given by: The equation for the first minimum is, then Similarly, each pair 2 and 6,3 and 7,4 and 8 differ in the path by λ/2 and will do the same. Thus, when these two rays reach point p on the screen they will interfere destructively. When these reach the wavefront AC, ray 5 would have a path difference ab say equal to λ/2. Let us consider rays 1 and 5 which are in phase on in the wavefront AB. In this figure, only nine rays have been drawn whereas actually there are a large number of them. It becomes simple to deal with rays instead of wavefronts as shown in the figure. These wavelets then interfere to produce the diffraction pattern. Each point of this section of the wavefront sends out secondary wavelets to the screen. A small portion of the incident wavefront passes through the narrow slit. The screen S is placed parallel to the slit for observing the effects of the diffraction of light. The slit AB of width d is illuminated by a parallel beam of monochromatic light of wavelength λ. The figure shows the experimental arrangement for studying diffraction of light due to the narrow slit. See Also : Interference of light Diffraction due to Narrow slit The diffraction of light occurs, in effect, due to the interference between rays coming from different parts of the same wavefront. The phenomenon is found to be prominent when the wavelength of light is compared with the size of the obstacle or aperture of the slit. These two experiments clearly show that when light travels past an obstacle, it does not proceed exactly along a straight path, but bends around the obstacle. According to Huygens’s principle, each point on the rim of the sphere behaves as a source of secondary wavelets which illuminate the central region of the shadow. The shadow of the spherical object is not completely dark but has a bright spot at its centre. Another simple experiment can be performed by exhibiting the same effect.Ĭonsider that a small and smooth ball of about 3 mm in diameter is illuminated by a point source of light.The shadow of the object is received on a screen as shown in the figure. If light travels in a straight path, the central region should appear dark i.e., the shadow of the screen between the two slits. In Young’s double-slit experiment for the interference of light, the central region of the fringe system is bright. See Also: Refraction of light Diffraction of light
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