IGNOU BPHCT-135 December 2022 Previous Year Question Paper

Q1.Attempt any five parts: 5x2=10

(a) Calculate the temperature at which the mean square speed of nitrogen molecules will be equal to 9 km sl. [Take R = 83 J/mol K, molecular weight of nitrogen = 28 g mol]

(b) What is the effect of pressure on viscosity ?

(c) State the third law of thermodynamics. Write its mathematical expression in terms of entropy.

(d) Define spectral emissive power of a body. How is it related to emissivity ?

(e) What is an intensive variable in a thermodynamic system ? Give one example.

(f) Write down the mathematical form of the first law of thermodynamics applied to a thermally insulated system. Comment on the nature of change in its internal energy.

(g) Draw the labelled diagram of phase space for a linear harmonic oscillator.

(h) Define Fermi energy. Plot Fermi function versus energy at T=0 K.

Q2.Attempt any fwo parts: 2x5=10

(a) One mole of CO, occupies 200 cm? at 34°C. Calculate the pressures exerted by CO, molecules, assuming that

(i) it obeys perfect gas equation, and

(ii) it obeys Van der Waal’s equation. It is given that a= 3-59 x 10-6 atm m$ mol, b = 42-7 x 10-6 m3 mol"! and R=82 x 10% atm m? K! mort. 243 BPHCT-135 2

(b) Define mean free path. How is it related with collision frequency ? If the radius of an oxygen molecule is 1-8 A and the mean speed of oxygen molecules at room temperature is 450 ms~, calculate mean free path. Take n= 3 » 10“ जाए, 14143

(c) Discuss Perrin’s method for determination of Avogadro number in Brownian motion. How can this method be used to estimate the mass of a molecule ?

Q3.Attempt any fwo parts : 2x5=10

(a) Explain the classification of boundaries in a thermodynamic system. 5

(b) State the Zeroth law of thermodynamics. How does it introduce the concept of temperature ? 243

(c) (Obtain an expression for work done in expanding a gas from volume V; to Vr in an isobaric process.

(ii) Two moles of an ideal gas occupy 0-035 m? volume at 2:6 x 10° Nm? pressure. It is expanded to volume 0-050 m? by isobaric process. Calculate the work done by the gas.

Q4.Attempt any two parts : 2x5=10

(a) With the help of Entropy-Temperature diagram of Carnot cycle, obtain an expression of efficiency of a Carnot engine. 5

(b) Obtain an expression for Clausius-Clapeyron equation. Explain why vegetables cook faster in a pressure cooker. 4+1

(c) Write Planck’s law in terms of wavelength. Hence, deduce Stefan’s Law.

Q5.Attempt any two parts: 2x5=10

(a) Define thermodynamic probability. How is it related to the entropy of a system ? Two systems have thermodynamic probabilities of 1:5 x 1076 and 2-0 x 1074. Calculate the entropies of the individual systems and the composite system. 1+1+3

(b) N particles obeying the Maxwell-Boltzmann statistics are distributed among three states with the energies E, = 0, Ey = 2 kpT and E, = 3 kpT. If the equilibrium energy of the system is 1000 kgT, calculate the total number of particles. 5

(c) Derive Planck’s Law using the Bose-Einstein Distribution Law for photons. 5 BPHCT-135 4 a = 3-59 x 10-6 atm m® mol, b = 42-7 x 10-6 m3 mol! ait R=82 x 10 atm m? K7! mol!.