B B1902 Pages: 2

light is 500nm.
18 Briefly explain the BCS theory of superconductivity. (4)
19 Obtain energy and momentum operators. (4)
8 20 State the postulates of Bose-Einstein statistics. (4)
21 The volume of a hall is 3000 1೫3. It has a total absorption of 100 (4)

m’Sabine. If the hall is filled with audience who add another 80m’Sabine, find
the difference in reverberation time. ١

22 Calculate the thickness of quartz crystal required to produce ultrasonic waves (4)
of frequency 1 MHz. Young’s modulus and density of quartz are 8 x 107
N/m’ and 2650 kg/m? respectively.

23 What is resonant cavity? What is its importance in the production of laser light? (4)
24 What is an LED? Give its working principle. What are the main uses of it? (4)
PART C

Answer any three questions, each carries 6 marks.

25 Frame the differential equation of a forced harmonic oscillator and obtain its (6)
solution.

26 Derive cosine law and explain colours in thin films in reflected light (6)

27 Distinguish between Type I and Type II superconductors citing examples. (6)
Explain the formation of Cooper pairs according to BCS theory.

28 State Uncertainity principle. Explain the absence of electron inside the nucleus (6)

using this principle.
PART D

Answer any three questions, each carries 6 marks.

29 Write any six factors affecting acoustics of buildings and their remedies. (6)

30 What are ultrasonic waves? What is NDT? Explain how the ultrasonic pulse (6)
technique is used for non-destructive testing of materials.

31 With a neat figure and energy level diagrams, explain the construction and (6)

working of a Helium-Neon laser.
32 With a neat diagram derive an expression for numerical aperture. Give any four (6)
applications of optical fibre.

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