106) A beam of light consisting of two wavelengths, 650 nm and 520 nm, is used to obtain interference fringes in a Young's double-slit experiment. What is the least distance from the central maximum where the bright fringes due to both the wavelengths coincide?

107) In a double-slit experiment the angular width of a fringe is found to be?0.2^??on a screen placed 1 m away. The wavelength of light used is 600 nm. What will be the angular width of the fringe if the entire experimental apparatus is immersed in water? Take refractive index of water to be 4/3.

108) What is the Brewster angle for air to glass transition? (Refractive index of glass = 1.5.)

109) Light of wavelength 5000 ? falls on a plane reflecting surface. What are the wavelength and frequency of the reflected light? For what angle of incidence is the reflected ray normal to the incident ray?

110) Estimate the distance for which ray optics is good approximation for an aperture of 4 mm and wavelength 400 nm.