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BSc (II Semester) Examination
PHYSICS
Paper : PHY–121 (Old Course)
( Heat and Thermodynamics )
Full Marks : 50
Pass Marks : 35%
Time : Two Hours
Note : 1. Section—A is compulsory and answer any four questions from Section—B.
2. The figures in the margin indicate full marks for the questions.
1. (a) “Internal energy is an extensive variable.” Explain. 2
(b) State Carnot’s theorem. 2
(c) What do you mean by degree of freedom? What will be the degree of freedom of a diatomic molecule at high temperature? 2
(d) Explain why is greater than . 2
(e) Give the limitations of 1st law of thermodynamics. 2
2. (a) What do you mean by adiabatic process? 2
(b) Deduce adiabatic equation of a perfect gas. 6
(c) Calculate the change in internal energy of a gas kept in a rigid container when 100 J of heat is supplied to it. 2
3. Derive van der Waals’ equation of state and use it to obtain the expression for
critical constant. 10
4. (a) Deduce the efficiency of a Carnot’s engine in terms of temperature between which it works. 7
(b) Efficiency of a Carnot’s cycle changes from 1/6 to 1/3 when source temperature is raised by 100 K. Calculate the temperatures of the source and sink. 3
5. (a) Deduce Clausius-Clapeyron equation. 6
(b) Why, at room temperature, hydrogen and helium gas show heating effect in porous plug experiment? 4
6. (a) What do you mean by entropy? Give the physical significance of entropy. 4
(b) Show that entropy of a system remains constant in reversible cycle. 6
7. Write short notes on any two of the following : 5×2=10
(a) Thermocouple thermometer
(b) Thermodynamic potentials
(c) Adiabatic demagnetization
(d) Enthalpy
