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12. An ideal gas is taken through the cycle A→ B → C → A, as shown in the figure. If the net heat supplied to the gas in the cycle is 5 J, the work done by the gas in the process C → A is

(a) – 5 J (b) – 10 J (c) – 15 J (d) – 20 J Answer-a (118)

11. The P-V diagram of a system undergoing thermodynamic transformation is shown in figure. The work done on the system in going from A → B → C is 50 J and 20 cal heat is given to the system. The change in internal energy between A and C is

(a) 34 J (b) 70 J (c) 84 J (d) 134 J Answer-d (202)

10. In pressure-volume diagram given below, the isochoric, isothermal, and isobaric parts respectively, are

(a) BA, AD, DC (b) DC, CB, BA (c) AB, BC, CD (d) CD, DA, AB Explanation-(d) Process CD is isochoric as volume is constant, Process DA is isothermal as temperature constant and Process AB is isobaric as pressure is …

9. Four curves A, B, C and D are drawn in the adjoining figure for a given amount of gas. The curves which represent adiabatic and isothermal changes are

(a) C and D respectively (b) D and C respectively (c) A and B respectively (d) B and A respectively Answer-c (105)

8. P-V plots for two gases during adiabatic process are shown in the figure. Plots 1 and 2 should correspond respectively to

(a) He and O2 (b) O2 and He (c) He and Ar (d) O2 and N2 Answer-b (138)

7. A thermodynamic process is shown in the figure. The pressures and volumes corresponding to some points in the figure are :

PA=3×104 Pa and PB=8×104 Pa, VA=2×10-3 m3 and VD=5×10-3 m3 . In process AB, 600 J of heat is added to the system and in process BC, 200 J of heat is added to the system. The change in internal energy …

6. Which of the following graphs correctly represents the variation of

β=-(dV/dP)/V with P for an ideal gas at constant temperature Answer-a (108)

5. An ideal gas of mass m in a state A goes to another state B via three different processes as shown in figure. If

Q1,Q2 and Q3 denote the heat absorbed by the gas along the three paths, then (a) Q1 < Q2 < Q3 (b) Q1 < Q2 = Q3 (c) Q1 =Q2 > Q3 (d) Q1 > Q2 > Q3 Answer-a (98)

27. A Carnot engine whose low temperature reservoir is at 7°C has an efficiency of 50%. It is desired to increase the efficiency to 70%. By how many degrees should the temperature of the high temperature reservoir be increased

(a) 840 K (b) 280 K (c) 560 K (d) 380 K Answer-d (81)

4. The P-V diagram shows seven curved paths (connected by vertical paths) that can be followed by a gas. Which two of them should be parts of a closed cycle if the net work done by the gas is to be at its maximum value

(a) ac (b) cg (c) af (d) cd Explanation-(c) Area enclosed between a and f is maximum. So work done in closed cycles follows a and f is maximum. (114)

3.An ideal gas is taken around ABCA as shown in the above P-V diagram. The work done during a cycle is

(a) 2PV (b) PV (c) 1/2PV (d) Zero Answer-a (45)

2. A thermodynamic system is taken through the cycle PQRSP process. The net work done by the system is

(a) 20 J (b) – 20 J (c) 400 J (d) – 374 J Ans. b (62)

1. A system goes from A to B via two processes I and II as shown in figure. If

ΔU1 and ΔU2 are the changes in internal energies in the processes I and II respectively, then (a) ΔUII > ΔUI (b) ΔU1 < ΔU2 (c) ΔU1 = ΔU2 (d) Relation between ΔUI and ΔUII can not be determined Ans. (c) …

30. Two cylinders A and B fitted with pistons contain equal amounts of an ideal diatomic gas at 300 K. The piston of A is free to move while that of B is held fixed. The same amount of heat is given to the gas in each cylinder. If the rise in temperature of the gas in A is 30 K, then the rise in temperature of the gas in B is

(a) 30 K (b) 18 K (c) 50 K …

29. Following figure shows on adiabatic cylindrical container of volume V0 divided by an adiabatic smooth piston (area of cross-section = A) in two equal parts. An ideal gas

(Cp/Cv=γ) is at pressure P1 and temperature T1 in left part and gas at pressure P2 and temperature T2 in right part. The piston is slowly displaced and released at a position where it can stay in equilibrium. The final pressure …

28. P-V diagram of a diatomic gas is a straight line passing through origin. The molar heat capacity of the gas in the process will be

(a) 4 R (b) 2.5 R (c) 3 R (d) 4R/3 Answer-c (9)

26.An ideal gas expands in such a manner that its pressure and volume can be related by equation

PV2= constant. During this process, the gas is (a) Heated (b) Cooled (c) Neither heated nor cooled (d) First heated and then cooled Answer-b (7)

25.Find the change in the entropy in the following process 100 gm of ice at 0°C melts when dropped in a bucket of water at 50°C (Assume temperature of water does not change)

(a) – 4.5 cal/K (b) + 4.5 cal/K (c) +5.4 cal/K (d) – 5.4 cal/K Answer-b (18)

24. An engineer claims to have made an engine delivering 10 kW power with fuel consumption of 1 g/sec. The calorific value of the fuel is 2 kcal/g. Is the claim of the engineer

(a) Valid (b) Invalid (c) Depends on engine design (d) Depends of the load Answer-b (2)

23. A reversible engine converts one-sixth of the heat input into work. When the temperature of the sink is reduced by 62°C, the efficiency of the engine is doubled. The temperatures of the source and sink are

(a) 80°C, 37°C (b) 95°C, 28°C (c) 90°C, 37°C (d) 99°C, 37°C Answer-d (4)

22.A thermally insulated rigid container contains an ideal gas heated by a filament of resistance 100Ω through a current of 1A for 5 min then change in internal energy is

(a) 0 kJ (b) 10 kJ (c) 20 kJ (d) 30 kJ Answer-d (8)

21. Initial pressure and volume of a gas are P and V respectively. First it is expanded isothermally to volume 4V and then compressed adiabatically to volume V. The final pressure of gas will be

(a) 1P (b) 2P (c) 4P (d) 8P Answer-b (6)

20. Two samples A and B of a gas initially at the same pressure and temperature are compressed from volume V to V/2 (A isothermally and adiabatically). The final pressure of A is

(a) Greater than the final pressure of B (b) Equal to the final pressure of B (c) Less than the final pressure of B (d) Twice the final pressure of B Answer-c (9)

19.Which one of the following gases possesses the largest internal energy

(a) 2 moles of helium occupying 1m3 at 300 K (b) 56 kg of nitrogen at 107N/m2 and 300 K (c) 8 grams of oxygen at 8 atm and 300 K (d) 6×1026 molecules of argon occupying 40m3 at …

18. When an ideal gas (γ=5/3 ) is heated under constant pressure, then what percentage of given heat energy will be utilised in doing external work

(a) 40 % (b) 30 % (c) 60 % (d) 20 % Answer-a (8)

17. When an ideal monoatomic gas is heated at constant pressure, fraction of heat energy supplied which increases the internal energy of gas, is

(a) 2/5 (b) 3/5 (c) 3/7 …

16. Two Carnot engines A and B are operated in succession. The first one, A receives heat from a source at

T1=800K and rejects to sink at T2K . The second engine B receives heat rejected by the first engine and rejects to another sink at T3=300K. If the work outputs of two engines are equal, then the value of T2 …

15. The temperature of a hypothetical gas increases to √2 times when compressed adiabatically to half the volume. Its equation can be written as

(a) PV3/2 = constant (b) PV5/2 = constant (c) PV7/3 = constant (d) PV4/3 = constant Answer-a (5)

14. The volume of air increases by 5% in its adiabatic expansion. The percentage decrease in its pressure will be

(a) 5% (b) 6% (c) 7% (d) 8% Answer-c (2)

13. An insulator container contains 4 moles of an ideal diatomic gas at temperature T. Heat Q is supplied to this gas, due to which 2 moles of the gas are dissociated into atoms but temperature of the gas remains constant. Then

(a) Q = 2RT (b) Q=RT (c) Q= 3RT (d) Q= 4RT Ans. b (3)

8. A gas mixture consists of 2 moles of oxygen and 4 moles argon at temperature T. Neglecting all vibrational modes, the total internal energy of the system is

(a) 4 RT (b) 15 RT (c) 9 RT (d) 11 RT Ans. d (6)

15. The temperature of a hypothetical gas increases to √2 times when compressed adiabatically to half the volume. Its equation can be written as

(a) PV3/2 = constant (b) PV5/2 = constant (c) PV7/3 = constant (d) PV4/3= constant Answer-a (7)

14. The volume of air increases by 5% in its adiabatic expansion. The percentage decrease in its pressure will be

(a) 5% (b) 6% (c) 7% (d) 8% Answer-c (4)

13. An insulator container contains 4 moles of an ideal diatomic gas at temperature T. Heat Q is supplied to this gas, due to which 2 moles of the gas are dissociated into atoms but temperature of the gas remains constant. Then

(a) Q=2RT (b) Q=RT (c) Q=3RT (d) Q=4RT Answer-b (7)

12. The molar heat capacity in a process of a diatomic gas if it does a work of Q/4 when a heat of Q is supplied to it is

(a) (2/5)R (b) (5/2)R (c) (10/3)R (d) …

11. A cylindrical tube of uniform cross-sectional area A is fitted with two air tight frictionless pistons. The pistons are connected to each other by a metallic wire. Initially the pressure of the gas is

P0 and temperature is T0, atmospheric pressure is also P0. Now the temperature of the gas is increased to 2T0, the tension in the wire will be (a) 2P0 A …

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