S A = 0.5 Id/4 8/2 d 179 S S A = 0.5" X, X2shaded region shown in liv Example 7.5: An isosceles prism of refracting angle 1790 and refractive index 1.5 is used as a biprism by keeping it 10 cm away from a slit, the edge of the biprism being parallel to the slit. The slit is illuminated by a light of wavelength 500 nm and the screen is 90 cm away from the biprism. Calculate the location of the centre of 20th dark band and the path difference at this location.Example 7.6: What must be the thickness of a thin film which, when kept near one of the slits shifts the central fringe by 5 mm for incident light of wavelength 5400 A in Young's double slit interference experiment? The refractive index of the material of the film is 1.1 and the distance between the slits is 0.5 mm