Waves and Optics — DU B.Sc. (Prog.) Physical Science courses pertaining to Electronics Previous Year Question Papers

2. Attempt FOUR questions in all. (a) Show that superposition principle is true only in case of homogeneous linear equations. (b) What are stationary waves? How are they formed? (c) In Young's double slit experiment, the separation of four bright fringes is 2.5 mm and the distance from the slit to the screen is 80.0 cm. Calculate the separation between two slits when the wavelength of the light used is 5896Å (d) Distinguish between Division of amplitude and Division of wavefront categories of interference. (e) What is the highest order spectrum which may be seen with a monochromatic light of wavelength 5000Å with a diffraction grating having 5000 lines/ 2. (a) What are Lissajous figures? Give a mathematical analysis to trace graphically the motion of a particle subjected to two perpendicular simple harmonic motions of equal frequencies, different amplitudes and phase differing by (i) zero and (ii) П/4. (b) All simple harmonic motions are periodic but all periodic motions are not simple harmonic. 3. (a) Explain the theory of formation of Newton's rings and derive an expression for the diameter of dark rings formed by reflected light. (10) (b) Newton's rings are observed in reflected light of wavelength 5900Å. The diameter of the 10th dark ring is 0.5 cm. Find the radius of curvature of the lens. (5) 4. (a) Give the theory of Fraunhofer diffraction due to a. single slit. Discuss the intensity distribution pattern obtained in it. (10) (b) For Fraunhoffer diffraction with a single slit of width 0.2 mm and screen placed at a distance of 3.0 m from the slit, find the total width of the central maximum, wavelength of light used is 5. (a) A set of 8 tuning forks is arranged in a series of increasing frequencies. If each fork gives 4 beats per second with the preceding one and the frequency of the last fork is an octave of the first, find the frequencies of the first and the last fork. (5) (b) Give Stokes treatment of reflection and refraction. (c) A parallel beam of light of wavelength 5890 A in incident on a glass plate (u=1.5) such that the angle of refraction into the plate is 60°. Calculate the smallest thickness of the plate which will make it dark by reflection. (5)