![]() These waves reinforce each other and give rise to the central maximum at point O.Let C be the center of the slit AB.The secondary waves, from points equidistant from center C of the slit lying on portion CA and CB of wave front travel the same distance in reaching O and hence the path difference between them is zero.Their combined effect at any distant point can be found y summing the numerous waves arriving there from the principle of superposition.According to Huygens principle each point t on unblocked portion of wavefront PQ sends out secondary wavelets in all directions Now consider a plane wave front PQ incident on the narrow slit AB. ![]() Thus diffraction pattern on screen consists of a central bright band and alternate dark and bright bands of decreasing intensity on both sides.The intensity of diffracted beam will be different in different directions and there are some directories where there is no light.All the rays that starts from slit AB in the same phase reinforce each other and produce brightness at point O on the axis of slit as they arrive there in the same phase.A real image of diffraction pattern is formed on the screen with the help of converging lens placed in the path of the diffracted beam.Let us first consider a parallel beam of light incident normally on a slit AB of width 'a' which is of order of the wavelength of light as shown below in the figure.Here in this chapter we will only be considering fraunhofer class diffraction by a single slit.This class of diffraction is simple to treat and easy to observe in practice Ii) Fruanhofer class of diffraction phenomenon where the source and the screen are at infinite distance from the aperture, this is easily achieved by placing the source on the focal plane of a convex lens and placing screen on focal plane of another convex lens. I) Fresnel class of diffraction phenomenon where the source of light and screen are in general at a finite distance from the diffracting aperture The diffraction phenomenon are usually divided into two classes.Thus we can explain diffraction phenomenon using Huygens�s principle.Fresnel then explained that the diffraction phenomenon was the result of mutual interference between the secondary wavelets from the same dif wave front.We now define diffraction of light as the phenomenon of bending of light waves around the corners and their spreading into the geometrical shadows.This effect of bending of beams round the corner was first discovered by grimed (Italy 1618-1663).Light like other waves also bends round corners but in comparison to sound waves small bending of light is due to very short wavelength of light which is of the order of 10 -5.It is a common observation with the waves of all kind that they bend round the edge of an obstacle.Vibrations in unpolarized and polarized light.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |