# Thermodynamics Test Questions - Set - 6

1)   A system will be in a state of thermodynamic equilibrium, if it undergoes.

a. mechanical equilibrium
b. chemical equilibrium
c. thermal equilibrium
d. all of the above
 Answer  Explanation  Related Ques ANSWER: all of the above Explanation: When a system does not have any unbalanced force within itself and also between the system and its surrounding then the system is in the mechanical equilibrium. When there is no chemical reaction or transfer of matter from one system to surrounding or vice versa then the system is said to be considered as chemical equilibrium. When there is no transfer of heat from one part to another when system and surrounding are distinguished by a diathermic wall (the wall which allows heat to flow) then the system is said to be in thermal equilibrium. A system will be in a state of thermodynamic equilibrium when it undergoes all there equilibriums.

2)   In electric resistance thermometer, the thermometric property is

a. electric current passing through a metal wire
b. resistance of a metal wire
c. voltage between two extreme end points of a metal wire
d. none of the above
 Answer  Explanation  Related Ques ANSWER: resistance of a metal wire Explanation: When current passes through a metal wire, as the temperature increases the resistance increases due to vibration of molecules in metal and collision of electrons carrying current. Therefore resistance of a metal wire is taken as a thermometric property in electric resistance thermometer. A suitable wire may be used for measuring temperature and the setup is arranged in a Wheatstone bridge circuit. Usually platinum wire is used as it can measure temperature to a high degree of accuracy and sensitivity. Platinum makes electric resistance thermometer suitable for the calibration of other thermometers.

3)   In free expansion of gas, the work transfer is

a. negative
b. zero
c. positive
d. none of the above
 Answer  Explanation  Related Ques ANSWER: zero Explanation: When a gas is expanded against vacuum then this expansion is called as free expansion. Work transfer is a boundary function as it is determined only at boundary. Let us consider a gas is separated from vacuum by a partition. Consider this as a system. When this partition is removed, the gas quickly fills up the vacuum area. If we do not consider the work related to removing the partition, then there is no work transfer involved here, because no work crosses the system boundary. Work is done by a system to overcome some resistance and to fill up the vacuum there is no any resistance to the gas to overcome. Therefore work transfer is zero in free expansion.

4)   A machine which can supply mechanical work continuously without consumption of any energy is called as

a. Perpetual Motion Machine of the First kind (PMM1)
b. Perpetual Motion Machine of the Second kind (PMM2)
c. Perpetual Motion Machine of the Third kind (PMM3)
d. none of the above
 Answer  Explanation  Related Ques ANSWER: Perpetual Motion Machine of the First kind (PMM1) Explanation: The first law of thermodynamics states that the energy can neither be created nor be destroyed. It can only gets transformed from one form to another form. Perpetual Motion Machine is the machine which violates the law of thermodynamics. A machine, which can supply mechanical work continuously without consumption of any energy, violates the first law of thermodynamics. Thus this machine is the Perpetual Motion Machine of the First kind (PMM1). When a machine violates the second law or third law of thermodynamics then this machine is called as PMM2 or PMM3 respectively. Perpetual Motion Machine is a hypothetical concept.

5)   Match the following group 1 items with group 2 items and select the correct option.

(1) PMM1 ---------------------------------- (A) Heat pump
(2) PMM2 ---------------------------------- (B) Violates the statement that total energy of the universe is constant
(3) Reversible heat engine ---------- (C) Violates Kelvin-Planck statement
(4) Carnot cycle ------------------------- (D) Reversible process

a. (1)-(A), (2)-(B), (3)-(C), (4)-(D)
b. (1)-(B), (2)-(D), (3)-(C), (4)-(A)
c. (1)-(B), (2)-(C), (3)-(A), (4)-(D)
d. (1)-(C), (2)-(D), (3)-(B), (4)-(A)
 Answer  Explanation  Related Ques ANSWER: (1)-(B), (2)-(C), (3)-(A), (4)-(D) Explanation: PMM1 is the machine which violates the first law of thermodynamics that the energy can neither be created nor be destroyed. Therefore total energy of the universe is constant. PMM2 is the machine which violates the second law of thermodynamics and Kelvin-Planck statement is one of the statements of second law thermodynamics. Reversible heat engine the engine which absorbs heat from low temperature body and supply it to high temperature body with the expense of external work on the system. This is the operation heat pump. And Carnot cycle is the cycle having all the processes reversible.

6)   The efficiency of the Carnot cycle is the function of

a. temperatures (T1, T2) between which the Carnot cycle operates
b. net work done (Wnet)
c. heat supplied (Q1) and heat rejected (Q2)
d. all of the above
 Answer  Explanation  Related Ques ANSWER: temperatures (T1, T2) between which the Carnot cycle operates Explanation: The efficiency of any heat engine is given byη = Wnet / Q1η = (Q1 – Q2) / Q1η = 1 – (Q2/Q1)It is necessary to know the temperature difference (T1 – T2) between which the cycle is operated. All the heat engines which are operating between the same temperature level have the same efficiency. It does not depend upon the working substance, work done or heat supplied. Therefore the efficiency of the Carnot cycle is the function of temperatures (T1, T2) between the Carnot cycle operates

7)   The Kelvin temperature scale is independent of the certain characteristics of any substance.

a. True
b. False

 Answer  Explanation  Related Ques ANSWER: True Explanation: The Kelvin temperature scale is nothing but the absolute thermodynamic temperature scale. As the heat is absorbed and rejected respectively by the Carnot engine operating between two reservoirs of different temperatures T1 and T2, these two temperatures on the Kelvin scale feature the same relationship with each other. Therefore, the Kelvin temperature scale is independent of the certain characteristics of any substance. It depends only on temperatures between which the heat engine works.

8)   Which point is taken as the standard reference point to define the Kelvin temperature scale?

a. Boiling point of water
b. Triple point of water
c. Freezing point of water
d. Boiling point of Mercury
 Answer  Explanation  Related Ques ANSWER: Triple point of water Explanation: The absolute thermodynamic temperature scale is also known as the Kelvin temperature scale. As the heat is absorbed and rejected respectively by the Carnot engine operating between two reservoirs of different temperatures T1 and T2, these two temperatures on the Kelvin scale feature the same relationship with each other.The heat absorbed and the heat rejected can be measured during two reversible isothermal and two reversible adiabatic processes in a Carnot engine. The triple point of water is used in defining the Kelvin temperature scale.

9)   Arbitrarily, the value of triple point is taken as

a. 0 K
b. 273.16 oC
c. 273.16 K
d. none of the above
 Answer  Explanation  Related Ques ANSWER: 273.16 K Explanation: As the heat is absorbed and rejected respectively by the Carnot engine operating between two reservoirs of different temperatures T1 and T2, these two temperatures on the Kelvin scale feature the same relationship with each other. The heat absorbed and the heat rejected can be measured during two reversible isothermal and two reversible adiabatic processes in a Carnot engine. The triple point of water is used in defining the Kelvin temperature scale. The triple point temperature of water is taken arbitrarily as 273.16 K

10)   The thermometric property in the Kelvin scale is _______

a. Temperature (T)
b. Work energy (W)
c. Heat energy (Q)
d. all of the above
 Answer  Explanation  Related Ques ANSWER: Heat energy (Q) Explanation: Consider the following diagram of heat engine which has sink at triple point of water. The Carnot heat engine takes heat Q from source at temperature T and produce work W and rejects heat Qt at sink which is at triple point of water. According to the definition of Kelvin scale,Q/Qt = T/ TtT = 273.16 (Q/Qt)From the above equation it is clear that Q that is heat plays a role of thermometric property. The amount of heat supply changes with change is temperature.

11)   How is the entropy of a closed system increased?

a. by interaction of heat
b. by internal irreversibilities
c. by dissipative effect in which work is dissipated to increase internal energy of the closed system
d. all of the above
 Answer  Explanation  Related Ques ANSWER: all of the above Explanation: No explanation is available for this question!

12)   The entropy generation

a. does not depend upon path followed by a system
b. depends upon path followed by a system
c. takes place in reversible process
d. none of the above
 Answer  Explanation  Related Ques ANSWER: depends upon path followed by a system Explanation: No explanation is available for this question!

13)   When a process followed by a system is irreversibilities, then what is the entropy generation of the system?

a. less than zero
b. equals to zero
c. greater than zero
d. none of the above
 Answer  Explanation  Related Ques ANSWER: greater than zero Explanation: No explanation is available for this question!

14)   Which thermodynamic process cannot be plotted accurately on thermodynamic coordinates?

a. reversible process
b. irreversible process
c. both reversible and irreversible processes
d. none of the above
 Answer  Explanation  Related Ques ANSWER: irreversible process Explanation: No explanation is available for this question!

15)   When the potential gradient in a process is infinitesimal or zero, what will be the change in entropy of the universe?

a. entropy increases
b. entropy decreases
c. no change in entropy
d. none of the above
 Answer  Explanation  Related Ques ANSWER: no change in entropy Explanation: No explanation is available for this question!

16)   What is the result of all the spontaneous processes in nature on the entropy of the universe?

a. All the spontaneous processes in nature increases the entropy on the universe
b. All the spontaneous processes in nature decreases the entropy on the universe
c. All the spontaneous processes in nature do not produce any change in the entropy on the universe
d. none of the above
 Answer  Explanation  Related Ques ANSWER: All the spontaneous processes in nature increases the entropy on the universe Explanation: No explanation is available for this question!

17)   The process which decreases the entropy of the universe is

a. reversible process
b. irreversible process
c. impossible process
d. none of the above
 Answer  Explanation  Related Ques ANSWER: impossible process Explanation: No explanation is available for this question!

18)   Two reversible processes undergone by a closed system between same two end states

a. produce different amounts of work
b. produce same amount of work if two systems are exchanging energy between themselves
c. produce same amount of work if two systems are exchanging energy with the surroundings
d. none of the above
 Answer  Explanation  Related Ques ANSWER: produce same amount of work if two systems are exchanging energy with the surroundings Explanation: No explanation is available for this question!

19)   How is the Helmholtz functions (F) represented?Where U represents internal energy
T represents temperature
S represents entropy

a. F = U + TS
b. F = U – TS
c. F = UT – S
d. F = UT + S
 Answer  Explanation  Related Ques ANSWER: F = U – TS Explanation: No explanation is available for this question!

20)   How is the Gibbs function (G) represented?
Where U represents internal energy
T represents temperature
S represents entropy

a. G = U + pV + TS
b. G = U – pV – TS
c. G = U + pV – TS
d. G = U – pV + TS
 Answer  Explanation  Related Ques ANSWER: G = U + pV – TS Explanation: No explanation is available for this question!

21)   If m1 and m2 are the masses of liquid and vapour respectively in a liquid-vapour mixture, then what is the formula for dryness fraction x?

a. x = (m1 + m2) / m1
b. x = (m1 + m2) / m2
c. x = m1 / (m1 + m2)
d. x = m2 / (m1 + m2)
 Answer  Explanation  Related Ques ANSWER: x = m2 / (m1 + m2) Explanation: No explanation is available for this question!

22)   What is the dryness fraction (x) for saturated water, when water just starts boiling?

a. x = 0
b. x = 1
c. x = 0.9
d. x = 0.5
 Answer  Explanation  Related Ques ANSWER: x = 0 Explanation: No explanation is available for this question!

23)   In high pressure condition, the real gases conform more closely with

a. van der Waals equation
b. ideal gas equation
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: van der Waals equation Explanation: No explanation is available for this question!

24)   What is reduced property of a substance?

a. critical property of a substance minus existing property of the same substance
b. existing property of a substance minus critical property of the same substance
c. ratio of critical property to existing property of the same substance
d. ratio of existing property to critical property of the same substance
 Answer  Explanation  Related Ques ANSWER: ratio of existing property to critical property of the same substance Explanation: No explanation is available for this question!

25)   The region at which the Joule-Kelvin coefficient is negative is called as

a. cooling region
b. heating region
c. negative region
d. positive region
 Answer  Explanation  Related Ques ANSWER: heating region Explanation: No explanation is available for this question!

26)   When the thermodynamic criterion of equilibrium (H, S, U, G or F) remains constant for all possible variation of finite magnitude then the system is said to be in

a. neutral equilibrium
b. unstable equilibrium
c. metastable equilibrium
d. none of the above
 Answer  Explanation  Related Ques ANSWER: neutral equilibrium Explanation: No explanation is available for this question!

27)   What is the unique feature of regenerative cycle over Rankine cycle?

a. the steam leaving the high pressure turbine again heated and used to run low pressure turbine
b. the condensate leaving the pump recirculated around the turbine case
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: the condensate leaving the pump recirculated around the turbine case Explanation: No explanation is available for this question!

28)   The net work output of an ideal regenerative cycle is

a. more than the net work output of the Rankine cycle
b. less than the net work output of the Rankine cycle
c. equal to the net work output of the Rankine cycle
d. cannot say
 Answer  Explanation  Related Ques ANSWER: less than the net work output of the Rankine cycle Explanation: No explanation is available for this question!

29)   Which among the following has the lowest efficiency than the others, when they are operated between same pressures?

a. Ideal Rankine cycle
b. Ideal regenerative cycle
c. Carnot cycle
d. None. All of the above have same efficiency
 Answer  Explanation  Related Ques ANSWER: Ideal Rankine cycle Explanation: No explanation is available for this question!

30)   What is the reason behind the fact that the ideal regenerative cycle is practically not possible?

a. The reversible heat transfer takes infinite time
b. It is mechanically impossible to exchange heat in the turbine
c. The moisture content of the steam in the turbine will be high
d. all of the above
 Answer  Explanation  Related Ques ANSWER: all of the above Explanation: No explanation is available for this question!

31)   How are the effect of reheat and effect of regeneration on the efficiency of steam power plant compared?

a. effect of reheat is greater that the effect of regeneration on plant efficiency
b. effect of regeneration is greater that the effect of reheat on plant efficiency
c. both the reheat and regeneration have same effect on efficiency of steam power plant
d. cannot say
 Answer  Explanation  Related Ques ANSWER: effect of regeneration is greater that the effect of reheat on plant efficiency Explanation: No explanation is available for this question!

32)   The feedwater heater in which the extracted steam and feedwater have thermal contact for exchanging heat but the extracted steam is not allowed to mix with the feedwater is called as

a. open type feedwater heater
b. contact type feedwater heater
c. closed type feedwater heater
d. none of the above
 Answer  Explanation  Related Ques ANSWER: closed type feedwater heater Explanation: No explanation is available for this question!

33)   The feedwater heater in which the extracted steam and feedwater are allowed to mix and both leave the heater at the same temperature, is called as

a. open type feedwater heater
b. contact type feedwater heater
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: both a. and b. Explanation: No explanation is available for this question!

34)   The maximum limit of the pressure ratio of the Brayton cycle for maximum efficiency

a. is less than the pressure ratio of the Carnot cycle
b. is more than the pressure ratio of the Carnot cycle
c. is equal to the pressure ratio of the Carnot cycle
d. cannot say
 Answer  Explanation  Related Ques ANSWER: is equal to the pressure ratio of the Carnot cycle Explanation: No explanation is available for this question!

35)   What is a free-shaft turbine?

a. the separate turbine which is used only to run compressor
b. the separate turbine which is placed on another shaft on which the compressor is not run
c. the separate turbine which is used only to run condenser
d. all of the above
 Answer  Explanation  Related Ques ANSWER: the separate turbine which is placed on another shaft on which the compressor is not run Explanation: No explanation is available for this question!

36)   What is the purpose of using free-shaft turbine?

a. to increase net work output of the turbine
b. to decrease net work output of the turbine
c. to increase part load efficiency
d. none of the above
 Answer  Explanation  Related Ques ANSWER: to increase part load efficiency Explanation: No explanation is available for this question!

37)   In the gas power plant, the free-shaft turbine is placed

a. right before the turbine used for running compressor
b. right after the turbine used for running compressor
c. right after the heat addition process
d. none of the above
 Answer  Explanation  Related Ques ANSWER: right after the turbine used for running compressor Explanation: No explanation is available for this question!

38)   Gas turbines are suitable for aircraft propulsion because

a. gas turbines are light weight
b. gas turbines are compact in size
c. gas turbines have a high power-to-weight ratio
d. all of the above
 Answer  Explanation  Related Ques ANSWER: all of the above Explanation: No explanation is available for this question!

39)   Which among the following engines is NOT the type of aircraft gas turbine which works on jet propulsion cycle?

a. turbojet
b. turbofan
c. turboprop
d. none of the above
 Answer  Explanation  Related Ques ANSWER: none of the above Explanation: No explanation is available for this question!

40)   What is the purpose of analyser-rectifire in aqua-ammonia absorption system?

a. to absorb ammonia into the water
b. to remove water vapour out from ammonia after generator
c. to exchange heat between weak solution and strong solution
d. none of the above
 Answer  Explanation  Related Ques ANSWER: to remove water vapour out from ammonia after generator Explanation: No explanation is available for this question!

41)   What is an advantage using analyser-rectifier in aqua-ammonia absorption system?

a. it makes ammonia-water solution strong
b. it prevents expansion valve from blocking due to ice formation
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: it prevents expansion valve from blocking due to ice formation Explanation: No explanation is available for this question!

42)   For a same pressure the saturation temperature of ammonia is

a. higher than the saturation temperature of water
b. lower than the saturation temperature of water
c. same as the saturation temperature of water
d. none of the above
 Answer  Explanation  Related Ques ANSWER: lower than the saturation temperature of water Explanation: No explanation is available for this question!

43)   Which type of energy is required to expend in vapour absorption refrigeration system?

d. none of the above

44)   The vapour absorption refrigeration system is

a. more noisy than the vapour compression refrigeration system
b. more silent than the vapour compression refrigeration system
c. equally noisy as the vapour compression refrigeration system
d. it depends upon plant capacity
 Answer  Explanation  Related Ques ANSWER: more silent than the vapour compression refrigeration system Explanation: No explanation is available for this question!

45)   For the same capacity of plant, the COP of the vapour absorption refrigeration system is

a. lower than the COP of the vapour compression refrigeration system
b. higher than the COP of the vapour compression refrigeration system
c. same as the COP of the vapour compression refrigeration system
d. cannot say
 Answer  Explanation  Related Ques ANSWER: lower than the COP of the vapour compression refrigeration system Explanation: No explanation is available for this question!

46)   On psychrometric chart, wet bulb temperature lines are

a. horizontal with uniformly spaced
b. horizontal with non-uniformly spaced
c. inclined with uniformly spaced
d. inclined with non-uniformly spaced
 Answer  Explanation  Related Ques ANSWER: inclined with non-uniformly spaced Explanation: No explanation is available for this question!

47)   At any point on the saturation curve in psychometric chart, the dry bulb temperature is always

a. less than the corresponding wet bulb temperature
b. more than the corresponding wet bulb temperature
c. equal to the corresponding wet bulb temperature
d. cannot predict
 Answer  Explanation  Related Ques ANSWER: equal to the corresponding wet bulb temperature Explanation: No explanation is available for this question!

48)   The moisture content lines in psychrometric chart are also called as

a. relative humidity lines
b. specific humidity lines
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: specific humidity lines Explanation: No explanation is available for this question!

49)   The natural draught in the steam generator depends upon

a. the air condition outside the chimney
b. the temperature of exhaust gases
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: both a. and b. Explanation: No explanation is available for this question!

50)   What is the disadvantage of natural draught?

a. it has less life
b. it has more maintenance cost of cleaning and more capital cost to build the chimney
c. the available draught decreases with increasing outside air temperature
d. all of the above
 Answer  Explanation  Related Ques ANSWER: the available draught decreases with increasing outside air temperature Explanation: No explanation is available for this question!