IGNOU BPHCT-137 June 2025 Previous Year Question Paper

Q1.Answer any five parts : 2x5=10

(a) State characteristic properties of a graded index multimode fiber.

(b) How is holography different from a photography?

(c) List three essential components required for laser operation.

(d) Draw intensity distribution of

(i) single slit and

(ii) double slit diffraction patterns.

(e) When one mirror of a Michelson interferometer is moved by a distance of 0.0112 cm, 400 fringes are seen to cross the field of view. Calculate the wavelength of light.

(f) Monochromatic light passes through two narrow slits 0.40 mm apart. The third order bright fringe in the interference pattern obtained on a screen placed 0.8 m from the slit is

Q2.6 mm from the centre of the central maximum. Calculate wavelength of light.

(g) Define birefringence. Give one example of a birefringence material.

(h) The intensity level of sound at a place is 40 dB. Calculate intensity of sound. Take threshold of hearing as 1x10-2 Wm.

Q3.Answer any two parts : 2x5=10

(a) Write the expression for speed of sound in air proposed by Newton. Write the discrepancy in this formula. How Laplace corrected the Newton’s formula ? 1+2+2

(b) A train whistle generates sound waves of frequency 480 Hz. If you are standing on the platform and the train moves towards you at 30 ms-!, what frequency will you hear ? Take the speed of sound to be 340 ms“.

(c) Consider a string of length L stretched between two fixed ends. A standing wave is generated on the string due to superposition. Obtain an expression for the fundamental frequency of the standing wave.

Q4.Answer any two parts : 2x5=10

(a) Two waves of equal frequency and having constant phase difference & while travelling in the same direction are superposed. Show that intensity of the resultant wave is given by I=a? + az + 26169 ९08 6 where a; and az are amplitudes of these waves.

(b) Newton’s rings arrangement is used with a source emitting two wavelengths : a1 = 5.4 x 10 cm and A2=4.5 x 10% cm It is found that nth dark ring due to A1 coincides with (n + 1)th dark ring due to Az. If the radius of curvature of the curved surface is 100 cm, find the diameter of the nth dark ring for 1.

(c) Discuss the working of Michelson interferometer with the help of an appropriate line diagram.

Q5.Answer any two parts: 2x5=10

(a) What is Nicol prism ? Discuss how linearly polarized light is obtained using a Nicol prism.

(b) Show that a zone plate acts like a converging lens.

(c) Calculate the maximum number of principal maxima that can be formed with a grating having 6250 lines per inch for light of wavelength 5000 A.

Q6.Answer any two parts: 2x5=10

(a) State the salient features of single slit diffraction pattern. In the diffraction pattern of a vertical slit of width

Q7.3 mm obtained on a screen at a distance of 30 cm, determine the angle and position of 1st, 2nd and 3rd minima. Take 4 = 6000 A

(b) With the help of a labelled diagram, explain the working of He—Ne laser.

(c) Discuss the applications of lasers in communication and research. I=a? + az +