LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034

XC 02

B.Sc. DEGREE EXAMINATION – PHYSICS

FIRST SEMESTER – April 2009

 PH 1502 / 1501 – PROPERTIES OF MATTER & ACOUSTICS

 

 

 

Date & Time: 22/04/2009 / 1:00 – 4:00   Dept. No.                                                   Max. : 100 Marks

 

 

PART A: ANSWER ALL QUESTIONS                                                      (10 x 2 = 20)           

 

• Define Poisson’s ratio.
• The Young’s modulus of a metal is 2×10¹¹N/m² and its breaking stress is 1.078×10⁹N/m². Calculate the maximum amount of energy per unit volume which can be stored in the metal when stretched.
• What is streamline motion?
• Define coefficient of viscosity. Give its SI unit.
• Give the dimension and unit of surface tension.
• Define the term angle of contact.
• State the principle of superposition of waves.
• What are beats?
• Define reverberation time.
• Give the principle of magnetostriction effect.

 

PART B: ANSWER ANY 4 QUESTIONS                                                          (4 x 7.5 = 30)

 

• (Show that.) Obtain a relation between the three elastic modulii.
• Discuss the working of a McLeod gauge.
• (a) A liquid drop of radius R breaks up into 64 small drops.  Calculate the change in energy.
  (b) An air bubble of radius 0.1mm is situated just below the surface of water.  Calculate the

excess pressure inside the air bubble. (Surface tension of water = 7.2 x 10^-2N/m).

• (a) Discuss the vibration of the air column in an open organ pipe.
  (b) An open organ pipe sounds the fundamental note of frequency 200Hz.  Find the length of the

pipe (velocity of sound in air is 350m/s).

• What is piezo-electric effect? Explain how this method is employed to produce ultrasonic waves. Mention any two applications of ultrasonics.

 

PART C: ANSWER ANY 4 QUESTIONS                                                           (4 x 12.5 = 50)

 

• (a) Derive an expression for the couple per unit twist due to torsional oscillations.

(b) Calculate the work done in twisting a steel wire of radius 10^-3m and length 0.25m through an

angle 45˚. Given rigidity modulus = 8×10¹⁰N/m².

 

• (a) Obtain Stoke’s law for the motion of a body in a viscous medium from dimensional

considerations.

 

 

(b) Find the limiting velocity of a rain drop.  (Given diameter of the drop = 10^-3m, density of air

relative to water = 1.3 x10^-3, coefficient of viscosity of air = 1.8 x 10^-5SI units and density of

water 10³kg/m³).

 

• a) Show that the vapor pressure on the curved surface of a liquid differs from that on the

plane surface of the same liquid by.
(b)  Calculate the difference in vapor pressure of water for a plane surface and for a drop of

radius 0.2mm.  Density of water vapor = 6 x 10^-4g/cm³ and surface tension of water = 70

dynes/cm.

 

• Explain Doppler effect. Derive an expression for the change in frequency of a note when
  • observer is at rest and source in motion
  • observer in motion and source is at rest and
  • observer and source in motion.

and Discuss the effect of wind.

 

• (a) Write down Sabine’s reverberation formula and explain the symbols.
  (b) Derive an expression to calculate the absorption coefficient.
  (c) The volume of a room is 600m³. The wall area of the room is 220m², the floor area is 120

m², and the ceiling area is 120 m².  The average sound absorption coefficient,

(i) for the walls is 0.03:

(ii) for the ceiling is 0.8 and

(iii) for the floor is 0.06.  Calculate the average sound absorption coefficient and reverberation

time.

 

 

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