IGNOU BPHCT-137 June 2023 Previous Year Question Paper

Q1.Attempt any five parts : 5×2=10

(a) Is it possible to lase a Ruby laser with excitation wavelength of 8000 Å ? Justify your answer.

(b) A note of a piano is sounded with a tuning fork of frequency 512 Hz. If eight beats are heard every second, calculate the frequency of the note.

(c) Construct wavefronts using Hu ygens’ principle.

(d) Show o- and e-wave surfaces in negative uniaxial crystal.

(e) Write two differences between biprism and Lloyd’s mirror fringes.

(f) Suppose the radius of the first half period of a zone plate is 0.4 mm. When a l ight of wavelength 6 × 10–5 cm is incident on the zone plate, it brings the rays of light to focus at its brightest point. Calculate the focal length of the zone plate.

(g) Depict intensity curve for a double shift diffraction pattern.

(h) Draw energy lev el diagram of helium -neon laser.

Q2.Answer any two parts : 2×5=10

(a) A progressive transverse wave is travelling on a string of length 3.0 m and mags 300 g. The tension in the string is 40 N. If the frequency and amplitude of the wave are 40 Hz and 6 mm, repectively, calculate the average power of the wave over one period.

(b) Show that speed of sound in air is given by : sound TV k

(c) What do you understand by the term reverberation ? What is its significance in design of a hall ?

Q3.Answer any two parts : 2×5=10

(a) The wavelength of an electromagnetic wave is 400 nm. The wave is travelling along the +y-direction and its  field is along the z-direction. Calculate the angular frequency and wave number of the wave. If the electric field amplitude is 500 V m–1, determine the amplitude of the magnetic field.

(b) What is polarization of light ? Discuss polarization by reflection.

(c) In a Young’s double slit experiment, a monochromatic light of wavelength 600 nm is used. One of the slits is covered by a transparent sheet of thickness

Q4.7 × 10–5 m and refractive index 1.6 . Calculate the number of fringes that will shift due to introduction of the sheet.

Q5.Answer any two parts : 2×5=10

(a) Show that the radii of dark rings obtained in the Newton’s ring experiment are proportional to the square root of the natural numbers.

(b) Explain how Michelson interf erometer can be used to determine wavelength of light.

(c) A coin has a diameter 2 cm. How many Fresnel zones will it cut -off if the scree n is 2 m away ? If the screen is further moved by 2 m, how many zones will be cut -off ? Take

Q6.Answer any two parts :

(a) Obtain Enistein ’s relations for abso rption and stimulated emission. 5

(b) Discuss applications of lasers in industry and environmental monitoring. 5

(c)

(i) Name the factors on which number of modes that can propagate i n a fibre depend. 2

(ii) Depict the modes that

( 1) a step index multimode and

(2 ) grade d index multimode fibre can support. 3 2023 -137

(ii)

(iii)

(iv) 5×2=10 8000 Å [ 7 ]