RGU Question Paper Physics Semester II 2020: Heat and Thermodynamics

 

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BSc (II Semester) Examination

PHYSICS

Paper : PHY–121 (New Course)

( Heat and Thermodynamics )

Full Marks : 60

Pass Marks : 35%

Time : Two Hours

Note : 1. Students have to attempt three questions out of five questions from Section—A and three questions from Section—B.
2. The figures in the margin indicate full marks for the questions.

Section—A

1. (a) What is Brownian motion? Why are the laws of kinetic theory of gases applicable to Brownian particles? 2+1=3

(b) Describe Einstein’s theory of Brownian motion. 7

2. (a) Deduce Clausius-Clapeyron equation. 4

(b) “The boiling point of the liquid is raised by increasing the pressure.” Explain on the basis of Clausius-Clapeyron equation. 2

(c) Water boils at a temperature of 101 °C at a pressure of 787 mm of Hg. 1 gm of water occupies 1601 $c{m}^{\mathrm{3 }}$on evaporation. Calculate the latent heat of steam. Given, $J=(4.42\times {10}^7 erg/cal)$ 4

3. (a) State Kirchhoff’s law of radiation. Derive the relation $E_{\lambda }=\frac{e_{\lambda }}{a_{\lambda }}$ , where $E_{\lambda }$ is the emissive power of a perfectly blackbody, $e_{\lambda }$ is the emissive power of a body and $a_{\lambda }$ is the adsorptive power of a body. 2+4=6

(b) State and deduce Stefan’s law. 1+3=4

4. Derive van der Waals’ equation of state and use it to obtain the expression for
critical constant. 10

5. Write short notes on any two of the following : 5×2=10
(a) Platinum resistance thermometer
(b) Kirchhoff’s law of radiation
(c) Gibbs phase rule
(d) Joule-Thomson effect

Section—B

6. (a) State and prove Carnot’s theorem. 6

(b) A heat engine operates between a cold reservoir at temperature $T_2=300 K$ and a hot reservoir at temperature $T_1$. It takes 200 J of heat from the heat reservoir and
delivers 120 J of heat to the cold reservoir in a cycle. What could be the minimum temperature of the heat reservoir? 4

7. (a) “Slope of the adiabatic curve is steeper than the slope of the isothermal curve.” Explain. 4

(b) State first law of thermodynamics “Perpetual motion machine of second kind is not forbidden by the first law of thermodynamics.” Explain. 2+4=6

8. (a) Show that the entropy of a system is a state function. 5

(b) Show that the entropy of a system increases in all irreversible processes. 5

9. Derive the following relations : 10

Here symbols have their usual meaning.

10. Write short notes on any two of the following : 5×2=10
(a) Adiabatic demagnetization
(b) Triple point
(c) Thermodynamic potentials