CHAPTER 10 THERMODYNAMICS

10.1      Multiple choice questions.

1.      When two bodies are made at thermal contact having the same temperature then they are at:
(a) Physical equilibrium	(b) Thermal equilibrium
(c) Mechanical equilibrium	(d) Chemical equilibrium
2.      Normal temperature of a man body is 98.6°F while its atmosphere temperature is 84. 6° F. What will be the temperature of the dead body in such atmosphere
(a) 86.4°F	(b) 98.6°F
(c) 92.5°F	(d) 185°F
3.      When the system is expanded by adding heat energy then the work done is:
(a) Positive and on the system	(b) Negative and on the system
(c) Positive and by the system	(d) Negative and by the system
4.      Which substance possesses the largest internal energy at t°C
(a) Solid	(b) Liquid
(c) Gas	(d) All of these
5.      Internal energy of a substance is defined in terms of
(a) P and V	(b) P and T
(c) T and V	(d) P, V and T
6.      The ratio between work done and heat energy is equal to:
(a) Adiabatic constant	(b) Joule’s constant
(c) Specific heat constant	(d) Real gas constant
7.      A system which transfers neither mass not energy is called;
(a) Open system	(b) Close system
(c) Isolated system	(d) Non-cyclic system
8.      First law of thermodynamics is based upon law of conservation of;
(a) Mass	(b) Energy
(c) Momentum	(d) Charges
9.      A process in which all the heat energy is used for increasing internal energy of the system is known as:
(a) Isobaric	(b) Isochoric
(c) Isothermal	(d) Adiabatic
10.  In which process the internal energy is used for doing work:
(a) Isobaric	(b) Isochoric
(c) Isothermal	(d) Adiabatic
11.  Specific heat of a gas in an isothermal process is:
(a) Zero	(b) Remains constant
(c) Negative	(d) Infinite
12.  A process in which the system remains at thermal equilibrium is known as:
(a) Isobaric	(b) Isochoric
(c) Isothermal	(d) Adiabatic
13.  The value of adiabatic constant for mono-atomic gas is
(a) 1.40	(b) 1.44
(c) 1.60	(d) 1.66
14.  The efficiency of a heat engine will be 100% when.
(a) Engine takes huge amount of heat from source	(b) Engine exhaust a very small amount of heat from sink
(c) The temperature of cold reservoir is 0°C	(d) The temperature of cold reservoir is 0 K
15.  Second law of thermodynamics provides the proper direction of;
(a) Temperature	(b) Force
(c) Pressure	(d) Flow of heat
16.  A device which converts mechanical energy into heat energy is known as:
(a) Heat engine	(b) Carnot Engine
(c) Refrigerator	(d) Turbine
17.  Entropy of a reversible process;
(a) Decreases	(b) Increases
(c) Infinite	(d) Zero
18.  Entropy remains constant in the process of;
(a) Isochoric	(b) Isobaric
(c) Isothermal	(d) Adiabatic

 

Answers

1. (b) Thermal equilibrium
2. (a) 86.4°F
3. (c) Positive and by the system
4. (c) Gas
5. (c) T and V
6. (b) Joule’s constant
7. (c) Isolated system
8. (b) Energy
9. (b) Isochoric
10. (d) Adiabatic
11. (a) Zero
12. (c) Isothermal
13. (d) 1.66
14. (d) The temperature of cold reservoir is 0 K
15. (d) Flow of heat
16. (a) Heat engine
17. (b) Increases
18. (d) Adiabatic

10.2      Short question

1. What is the condition of perfect thermal equilibrium?

ans.    When two or more system are at the same temperature     and there is no net heat between them then the system is said to be perfect thermal equilibrium.

7. Why the measurement of molar specific heat is being preferred than specific heat?

ans.    Because one mole of any substance contains the same number of molecules which is more preferred than specific heat.

9. What is the difference between reversible and irreversible process?

ans.    A reversible process is a process that can be reversed to return the system and its surrounding to their original states, with no generation of entropy. For example, the conversion of the ice into water then water into ice. While irreversible process generate entropy in the system and can’t be retraced in the exact order. For example, flow of heat from hot body to a cold body is an irreversible process.

14. What will be the work done of a system when it’s hot and cold reservoirs are at same temperature?

ans.         If the hot and cold reservoir of a system are at the same temperature, then no work is done because no temperature difference and no heat transfer can occur.

10.3      Numerical problems

2. A sample of gas is compressed to one half of its initial volume at constant  pressure of 1.25 x 10⁵ Nm^-2. During the compression, 100 J of work is done on the gas; determine the final volume of the gas.

5. A mechanical engineer develops an engine, working between 327°C and 27°C and claims to have an efficiency of 50%. Does he claim correctly? Explain.

9. How much work does on ideal Carnot refrigerator require to remove 1 J of energy from helium at 4k and reject this thermal energy to a room temperature 293 K environment.