1. Attempt any three parts

(a) Show that, in vacuum, the wave equation for the electric field vector, E is

<img src='./qimages/12716-1a.jpg'> Draw the ray diagram showing the formation of coherent sources by a biprism. State three important differences' between the interference fringe patterns produced by biprism and Lloyd's mirror. With appropriate diagrams, explain Rayleigh's criterion for resolution. A big plane metal sheet· has a circular aperture of diameter 2 mm. A beam of parallel light of wavelength 5000 A is incident upon it normally. The shadow is cast on a screen whose distance can be varied continuously. Calculate the distance at which the aperture will transmit 3 Fresnel Zones. Draw the energy level diagram of a He-Ne laser indicating the lasing transitions. Write the wavelengths corresponding to lasing transitions.

2. Attempt any one parts Discuss polarisation of light due to reflection. State Brewster's law. List the processes involved in image formation by unaided eye. Explain any one of them.

3. Attempt any two parts: Discuss the use of Michelson interferometer for determining the refractive index of a thin transparent plate. Show that the radius of dark rings in 'Newton's rings experiment is proportional to the .square root of natural numbers. In a Newton's rings experiment, the diameter of the 7th and 18th dark rings are 0.386 em and O.663 cm respectively. If the light of wavelength 5890 A has been used in the experiment, calculate the radius of curvature of planoconvex lens. Light is incident obliquely on a thin film of thickness t and refractive index u. Show that the condition for constructive interference in reflected light is given by <img src='./qimages/12716-3c.jpg'>

4. Attempt anyone part Write down the salient features of Fraunhofer diffraction pattern due to a single slit. Derive an expression for the intensity distribution in the Fraunhofer diffraction pattern due to single slit.
What is a zone plate? What is the difference between a positive and a negative zone plate Show that a zone plate acts like a converging lens.

5. Attempt any two parts: Distinguish between spontaneous emission and stimulated emission. Discuss the importance of population inversion for lasers. What are the salient features of a hologram Discuss the reconstruction of image from a hologram. What is a step-index fibre Obtain an expression for the angle of incidence beyond which light will get refracted into the cladding material. What will happen if the refractive index of the cladding is higher than that of the core?