Engineering Physics

14.7 Fraunhofer diffraction at single slit

The single slit is represented as AB in Fig. 14.8. The slit is in the form of a narrow rectangle in shape. The width of the slit AB is equal to ‘e’ and the plane of the slit is perpendicular to the plane of the paper. A plane wave front WW of monochromatic light of wave length ‘λ’ is incident on the slit AB. Every point on the wave front in the slit will act as a source of secondary wavelets. The secondary wavelets travelling in the direction of OP are brought to focus at P₀ on the screen SS by using a converging lens L. The secondary wavelets from AB which are brought to focus at P₀ have no path difference. Hence the intensity at P₀ is high and it is known as central maximum. The secondary wavelets ...