IGNOU BPHCT-137 June 2022 Previous Year Question Paper

Q1.Attempt any five parts : 5x2=10

(a) If the amplitude of a wave is doubled, by what factor will its energy change ?

(b) Is it correct to say that on a standing wave formed on a string fixed at both ends, we observe antinodes at the fixed ends ? Justify your answer.

(c) Write any two differences between the fringes obtained using a biprism and a Lloyd’s mirror.

(d) State the principle of optical reversibility.

(e) What is the path difference between the waves emanating from two consecutive transparent zones of a zone plate ?

(f) Explain briefly how gratings are used in spectroscopy.

(g) Draw the energy level diagram for a three-level pumping scheme in a Ruby laser.

(h) List two basic differences between a hologram and a normal photograph.

Q2.Attempt any fwo parts: 2x5=10

(a) Show that the speed of sound in a gaseous medium is proportional to the square root of temperature. 5

(b) Two light waves having different frequencies and wavelengths are propagating in free space. Do they travel with the same speed ? Justify your answer. Also, calculate the frequency of the electromagnetic wave having wavelength 110 m. (Givenc=3x108 ms!) 342

(c) A slab of glass having refractive index 1-5 is immersed in water. Calculate the polarising angle for a beam of light incident from

(i) glass on to glass-water interface, and

(ii) water on to water-glass interface. Take refractive index of water to be 1:25.

Q3.Attempt any fwo parts : 2x5=10

(a) Derive an expression for the displacement of the n‘® bright fringe in Young’s double-slit experiment when a thin transparent plate (of mica or glass) of refractive index » and thickness t is introduced in the path of one of the constituent interfering beams of light. 5

(b) Newton’s rings are formed in reflected light of wavelength 5890 x 10-8 cm with a liquid between the plane and the curved surfaces. The diameter of the fifth ring is 0-3 cm and radius of curvature of the curved surface is 100 cm. Calculate the refractive index of the liquid when the ring is dark. 5

(c) Explain how Michelson interferometer is used for determination of the difference in wavelengths.

Q4.Attempt any one part : 1x10=10

(a) Derive an expression for the intensity distribution in the Single Slit Fraunhofer diffraction pattern. 10

(b) G) A coin has a diameter of 2-5 cm. How many Fresnel zones does it cut off if the screen is 2-0 m away ? If the screen is moved to a distance of 3-0 m, how many zones will it cut off ? (Take 4 = 5 x 1077 m) 5 Gi) Monochromatic light of wavelength 500 nm illuminates a_ diffraction grating having 2000 lines. If the value of the grating element is 16 um, calculate the angular half-width of the first order principal maxima.

Q5.Attempt any two parts: 2x5=10

(a) What is speckle pattern of laser light ? Explain the formation of speckle pattern from a rough surface. 1+4

(b) In an optical fibre, the refractive index of core is 1-51 and that of cladding is 1-46. Calculate its critical angle, numerical aperture and acceptance angle in air. 24+2+1

(c) With the help of energy level diagram, explain the spontaneous emission, absorption and stimulated emission of light.