### AU Degree 4th Sem Physics (2018) Question Paper

**B.Sc. Degree Examination.**

**(Examination at the end of Semester - IV)**

**Part Il: PHYSICS**

**Thermodynamics and Radiation Physics**

**[Section - A] (5 x 5 = 25 Marks)**

**Answer any Five from the following Eight questions.**

1. Derive an expression for the thermal conductivity of the gas.

2. What is entropy ? Give its physical significance.

3. Explain thermodynamic potentials.

4. Explain Kapitza’s method for the Liquefaction of helium.

5. Discuss the distribution of energy in the spectrum of black body radiation.

6. The RMS speed of the hydrogen molecule is 1.84 km/sec. What will be the RMS speed of oxygen molecule of the same temperature?

7. A reversible engine works between two temperatures whose difference is 100° C. It absorbs 746 J of heat from the source and given 546 J to sink, calculate the temperature of source and sink.

8. Find the wavelength at which maximum energy is radiated by a black body having a temperature of 327° C. The Wein's constant is 2.897 x 10

^{-1}?

**[Section - B] (5x10=50 Marks)**

**Answer All Questions.**

9. (a) State Maxwell's law of distribution of velocities and obtain an expression for the average speed.

Or

(b) Obtain an expression for the mean free path of the molecule of gas and show that it is inversely proportional to the pressure of the gas.

10. (a) Distinguish between isothermal and adiabatic process and derive an expression for the work done in the isothermal process.

Or

(b) Explain the T-S diagram and obtain an expression for the efficiency of a Carnot engine using the T-S diagram.

11. (a) Derive Clausius-Clapeyron's equation using Maxwell's equations and give its applications.

Or

(b) Obtain an expression for the difference between two molar specific heats Cp and Cy of a perfect gas.

12. (a) Describe Porous plug experiment demonstrating the Joule-Kelvin effect.

Or

(b) Explain the adiabatic demagnetization method for producing low temperatures.

13. (a) Deduce Rayleigh-Jean's radiation law from Planck's radiation law.

Or

(b) Describe the construction and working of a total radiation pyrometer.

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