1. Attempt any three parts State Fermat's principle. Derive the laws of refraction using it. Obtain an expression for the fringe shift when a thin glass plate is introduced in the path of one of the interfering beams in a double slit interference experiment. Deduce an expression for the resolving power of a microscope. A diffraction-limited laser beam =6300 of diameter 5 mm is directed at the Earth from a space laboratory orbiting at an altitude of 600 km. How large an area would the central beam illuminate? With the help of the refractive index profile, distinguish between the step-index fibre and the gradient-index fibre. Why, in an optical fibre, should the refractive index of the core be higher than that of the cladding?

2. Attempt anyone part Define Poynting vector and state its significance.

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A plate of flint glass is immersed in water. Calculate the Brewster angle for internal as well as external reflection at an interface. Take the refractive index of flint glass and water as 1.67 and 1.33, respectively.

3. Attempt any two parts: What do you understand by division of wavefront and division of amplitude Explain the formation of coherent sources in the interference experiment set-up using Lloyd's mirror.
Two waves of the same frequency and constant phase difference have intensities in the ratio 36 4. These waves are superposed and Interference fringe pattern. is obtained. Calculate the ratio of the maximum to minimum intensity. Explain the determination of the difference in the wavelengths of two nearly equal wavelengths using a Michelson interferometer.

4. Attempt anyone part Explain the concept of half period elements and show that individual Fresnel zones have approximately the same area. The seventh boundary of a zone plate has a diameter of 5 mm. Calculate its principal focal length for light of wavelength 5000 A. Write down the salient features of the double slit diffraction pattern. Derive an expression for the intensity distribution in double slit diffraction pattern.

5. Attempt any two parts What are the pre-requisites of a laser Discuss the applications of laser in communication. Explain the basic principle of holography. With the help of a diagram, describe the production of hologram. Derive an expression for the light gathering capacity of an optical fibre. Suppose the refractive indices of core and cladding of an optical fibre are 1.53 and 1.39, respectively. Calculate the numerical aperture of the fibre.