The incident wave fronts are either spherical or cylindrical.,, Fraunhofer diffraction,, In this class of diffraction, the source and screen are placed at infinite distances, from the obstacle. This diffraction can be studied in the direction of, propagation of light. To study this diffraction, lenses are not necessary as the source and, screen are at a finite distance. In this, class of diffraction, the source and screen are placed at finite distances from the, obstacle. The, bright and dark fringes in the shadow forms a diffraction pattern., The diffraction phenomena are broadly classified into two types.,, Fresnel diffraction,, To study diffraction, there should be a light source, obstacle and screen. This bending of light is known as diffraction. These fringes are due, to the superimposition of bended light waves around the corners of an obstacle., The amount of bending depends upon the size of an obstacle and wavelength of, light.,, ,, ,, ,, ,, Screen,, Light | A A!, -_>, - Geometrical Shadow, -,, i BI,, B,, | Obstacle,, Figure 2.1 Diffraction,, When light falls on an obstacle whose size is comparable with the wavelength, of light then light bends around the edges or corners of an obstacle and entersĮngineering Physics,, 22 iy,, into the geometrical shadow. In practice, the, geometrical shadow consists of bright and dark fringes. 2.1, when light falls on an obstacle then the corresponding, geometrical shadow on the screen should be completely dark. It was first observed by Gremaldy.,, 2.1 DIFFRACTION,, As shown in Fig. The bending of light waves, around the edge of an obstacle is diffraction. This bending is predominant when the size of the, obstacle is comparable to the wavelength of light. When light waves encounter an obstacle, they bend, round the edges of the obstacle. It is common experience that waves bend around, obstacles placed in their path. The word ‘diffraction’ is derived from the Latin word diffractus, which means to break to pieces. ,, _ INTRODUCTION,, ,, The wave nature of light is further confirmed by the optical phenomenon of, diffraction. [CHAPTER 2°,, DIFFRACTION,, 2,, ,, ,, ) what ave the lypes oF dP and guee be difleencee hebucen Bern,, due.,, 2) ob m the condition abe py Ory maxima imbeitho Pec di PRo ifs y,, Single elit anddeve an ex preasion Bax caiich bs of Peete,, pax me.
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