# Thermodynamics Test Questions - Set - 7

1)   Quasi-static process

a. is infinitely slow process
b. experiences thermodynamic equilibrium at every small point on its path
c. reversible process
d. all of the above
 Answer  Explanation  Related Ques ANSWER: all of the above Explanation: Consider a system of gas exists in a cylinder. The piston consists of many very small pieces of weights. Initially system is in an equilibrium state. When the gas system is isolated, the weights on piston are removed one by one slowly, at any instant of upward travel of the piston. So every state passes through by the system will be in an equilibrium state. Thus the system passes through the locus of all equilibrium points. This infinitely slow system is a quasi-static process. If the same small weights are now placed slowly one by one on top of the piston then the process will reverse in the same manner.

2)   The thermocouple circuit which is used to measure temperature works on ____.

a. Seebeck effect
b. Peltier effect
c. Thomson effect
d. none of the above
 Answer  Explanation  Related Ques ANSWER: Seebeck effect Explanation: The Seebeck effect states that when two ends of a thermocouple are kept at different temperatures then the emf is generated in the circuit depending on the temperature difference between the hot and the cold junction. Therefore emf is a thermometric property of the circuit. The thermocouple is calibrated by measuring the thermal emf at various known temperatures, the reference junction being kept at 0° C. Peltier effect is exact opposite of Seebeck effect that the temperature difference is created by applying the voltage between two junctions of thermocouple circuit.

3)   Heat is transferred across a boundary by virtue of a temperature difference. The heat is transferred, that means

a. force transfer takes place
b. energy transfer takes place
c. temperature transfer takes place
d. all of the above
 Answer  Explanation  Related Ques ANSWER: energy transfer takes place Explanation: When a system changes its state from state 1 to state 2, the work involved depends upon the path through which the system undergoes change. For consistency with the principle of conservation of energy, some other type of energy transfer along with work transfer must have taken place between the system and surrounding. This type of 'energy transfer' is occurred by virtue of a temperature difference. This energy is called as 'heat'.

4)   Total amount of energy in the universe is

a. increasing
b. decreasing
c. constant
d. none of the above
 Answer  Explanation  Related Ques ANSWER: constant Explanation: The first law of thermodynamics states that the energy can neither be created nor be destroyed. It can only get transformed from one form to another form. The universe consists of the system as well as the surrounding together. Energy can only be transferred from system to surrounding or surrounding to system in various forms, but it can never be destroyed or created. Thus the total amount of energy in the universe is constant. We cannot produce a device which can supply mechanical work without consuming any energy.

5)   To achieve a definite zero point on the Kelvin scale, we have to violate

a. first law of thermodynamics
b. second law of thermodynamics
c. both first law and second law of thermodynamics
d. no law has to be violated
 Answer  Explanation  Related Ques ANSWER: second law of thermodynamics Explanation: To achieve a definite zero point on the Kelvin scale or absolute zero temperature scale, we have to consider a series of reversible engines, passing from a source at T1 to lower temperatures. Consider the following diagram, The heat engine E1 is operating between temperatures T1 and T2.Therefore,( T1 / T2 ) = ( Q1 /Q2 )( T1 – T2 ) / T2 = ( Q1 – Q2 ) / Q2( T1 – T2 ) = ( Q1 – Q2 ) ( T2 / Q2 )Similarly,( T2 – T3 ) = ( Q2 – Q3 ) ( T3 / Q3 )and so onIf we make this series of heat engines continue so that the total work output equals to heat supplied Q1. This means there will not be any heat rejection and definite zero point on the Kelvin scale is achieved. But as there is no any heat rejection means total heat supplied is completely converted into work output. This condition violates the second law of thermodynamics.

6)   The temperature at which a system undergoes a reversible isothermal process without transfer of heat is called as _________

a. critical temperature
b. Kelvin temperature
c. absolute zero temperature
d. reversible temperature
 Answer  Explanation  Related Ques ANSWER: absolute zero temperature Explanation: According to the definition of Kelvin scale,Q/Qt = T/ TtT = 273.16 (Q/Qt)from the above equation, it is clear that the heat transferred isothermally between two adiabatic bodies decreases if temperature decreases. Here Qt is the thermometric property. Therefore, from above equation if Q is having smaller value then T also lowers. The smallest possible value of Q is zero and corresponding T is zero. Thus, the temperature at which a system undergoes a reversible isothermal process without transfer of heat is called as absolute zero. At absolute zero, an isotherm and adiabatic are identical.

7)   Any attainable value of absolute temperature is ________

a. always less than zero
b. always equals to zero
c. always greater than zero
d. none of the above
 Answer  Explanation  Related Ques ANSWER: always greater than zero Explanation: It is impossible for a system to undergo a reversible isothermal process without transfer of heat. To make this process possible, the temperature required is an absolute zero temperature and the second law of thermodynamics is also violated. Thus any attainable value of absolute temperature is always greater than zero. This is also called as third law of thermodynamics. It states that it is impossible for any process to reduce any system to an absolute zero temperature in a finite number of operations.

8)   Assume that a reversible heat engine is operating between a source at T1 and a sink at T2. If T2 decreases, the efficiency of the heat engine  ______

a. decreases
b. increases
c. remains constant
d. none of the above
 Answer  Explanation  Related Ques ANSWER: increases Explanation: The efficiency of a reversible heat engine is operating between a source at T1 and a sink at T2 is given by,η = Work done / Heat suppliedηrev = ηmax = ( T1 – T2 ) / T1ηrev = 1 – (T2/T1)From the above equation, as T2 decreases the efficiency increases and tends towards 100%

9)   The irreversibility in the system caused by friction is an example of

a. internal irreversibility
b. external irreversibility
c. frictional irreversibility
d. chemical irreversibility
 Answer  Explanation  Related Ques ANSWER: internal irreversibility Explanation: All the spontaneous processes are irreversible in nature. The irreversibility is caused by finite potential gradient like temperature gradient etc. or by any dissipative effect like friction. There are two types of irreversibilityi. Internal irreversibilityii. External irreversibilityInternal irreversibility is caused by internal dissipative effects in the system like friction, turbulence, electric resistance etc. Thus the irreversibility in the system caused by friction is an example of internal irreversibility.

10)   When a process becomes irreversible due to heat interaction between system and surrounding at the boundary due to finite temperature gradient, then the irreversibility is______

a. internal irreversibility
b. external irreversibility
c. mechanical irreversibility
d. chemical irreversibility
 Answer  Explanation  Related Ques ANSWER: external irreversibility Explanation: All the spontaneous processes are irreversible in nature. The irreversibility is caused by finite potential gradient like temperature gradient etc. or by any dissipative effect like friction. There are two types of irreversibilityi.) Internal irreversibilityii.) External irreversibilityThe external irreversibility occurs due to the temperature difference between the source and a working fluid at heat supply and the temperature difference between the sink and the working fluid at heat rejection. If the hypothetical heat source and sink is considered then the process becomes reversible.

11)   The degree of disorder of a mixture of two gases

a. is always less than the degrees of disorder of individual gases
b. is always greater than the degrees of disorder of individual gases
c. is always equals the degrees of disorder of individual gases
d. none of the above
 Answer  Explanation  Related Ques ANSWER: is always greater than the degrees of disorder of individual gases Explanation: No explanation is available for this question!

12)   What is the relation between thermodynamic probability (W) and entropy?

a. thermodynamic probability increases with entropy
b. thermodynamic probability decreases with entropy
c. thermodynamic probability does not change with change in with entropy
d. none of the above
 Answer  Explanation  Related Ques ANSWER: thermodynamic probability increases with entropy Explanation: No explanation is available for this question!

13)   At the most probable state of a system the entropy of the system is

a. minimum
b. maximum
c. constant
d. none of the above
 Answer  Explanation  Related Ques ANSWER: maximum Explanation: No explanation is available for this question!

14)   If the two parts A and B in a system are considered to be in equilibrium and having thermodynamic probabilities WA and WB, what will be the thermodynamic probability of the system?

a. W = WA . WB
b. W = WA + WB
c. W = (WA + WB) / 2
d. W = √(WA – WB)
 Answer  Explanation  Related Ques ANSWER: W = WA . WB Explanation: No explanation is available for this question!

15)   At the state of perfect order (W = 1) of pure crystalline substance, how is the zero entropy defined?

a. entropy at 0 °C temperature
b. entropy at absolute zero temperature
c. entropy at the freezing point of the substance
d. none of the above
 Answer  Explanation  Related Ques ANSWER: entropy at absolute zero temperature Explanation: No explanation is available for this question!

16)   What is the reason behind the fact that the absolute zero entropy value is not attainable?

a. because absolute zero temperature is not attainable in finite number of operations
b. because theoretically absolute zero temperature has negative value of entropy and it is not possible
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: because absolute zero temperature is not attainable in finite number of operations Explanation: No explanation is available for this question!

17)   What is the entropy chosen at the triple point of water?

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

18)   What is the difference between work done by a system through an ideal reversible process and actual work done by the system called?

a. irreversibility
c. dissipation
d. all of the above
 Answer  Explanation  Related Ques ANSWER: all of the above Explanation: No explanation is available for this question!

19)   Which will be a suitable condition of exergy loss and entropy generation for thermodynamically efficient process?

a. maximum exergy loss with minimum rate of entropy generation
b. minimum exergy loss with maximum rate of entropy generation
c. maximum exergy loss with maximum rate of entropy generation
d. minimum exergy loss with minimum rate of entropy generation
 Answer  Explanation  Related Ques ANSWER: minimum exergy loss with minimum rate of entropy generation Explanation: No explanation is available for this question!

20)   What is the value of exergy in general?

a. only negative
b. only positive
c. sometimes positive sometimes negative
d. cannot say
 Answer  Explanation  Related Ques ANSWER: only positive Explanation: No explanation is available for this question!

21)   What is the dryness fraction (x) on saturated vapour line?

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

22)   What is the line which starts from critical point having constant dryness fraction throughout the line as shown in figure (Line1) called? a. constant vapour line
b. constant liquid line
c. constant quality line
d. none of the above
 Answer  Explanation  Related Ques ANSWER: constant quality line Explanation: No explanation is available for this question!

23)   In a mixture of ideal gases of volume V and temperature T, what is the pressure exerted by each individual gas if it occupies the total volume V alone at temperature T called?

a. individual pressure
b. divided pressure
c. partial pressure
d. total pressure
 Answer  Explanation  Related Ques ANSWER: partial pressure Explanation: No explanation is available for this question!

24)   A mixture of ideal gases of volume V at temperature T, contains n1 moles of gas A, n2 moles of gas B and n3 moles of gas C. What is a correct formula for partial pressure (pB) of gas B?

a. (pB) = ((1/3)(n1+n2+n3) RT) / V

b. (pB) = ((n1 + n3) RT) / V
c. (pB) = (n2 RT) / V
d. (pB) = (n2(n1 + n3) RT) / V
 Answer  Explanation  Related Ques ANSWER: (pB) = (n2 RT) / V Explanation: No explanation is available for this question!

25)   What is the entropy change when the system is at stable equilibrium state?

a. the entropy change will be positive
b. the entropy change will be negative
c. the entropy change will be zero
d. cannot say
 Answer  Explanation  Related Ques ANSWER: the entropy change will be zero Explanation: No explanation is available for this question!

26)   What is the entropy of the system at equilibrium state?

a. zero
b. minimum
c. maximum
d. constant but not maximum
 Answer  Explanation  Related Ques ANSWER: maximum Explanation: No explanation is available for this question!

27)   A closed feedwater heater system

a. has high heat transfer capacity
b. requires pump at each heater to handle the large feedwater stream
c. requires only single pump regardless of the number of heaters
d. does not require any pump as the extracted steam and feedwater are not allowed to mix
 Answer  Explanation  Related Ques ANSWER: requires only single pump regardless of the number of heaters Explanation: No explanation is available for this question!

28)   What is the drawback of the steam as a working substance in a power cycle?

a. in a vapour power cycle, maximum temperature which can be obtained with best available material is more than the critical temperature of water and requires large superheating
b. it allows only small amount of heat addition at the highest temperature
c. it requires reheat and reheater tubes are costly
d. all of the above
 Answer  Explanation  Related Ques ANSWER: all of the above Explanation: No explanation is available for this question!

29)   As the heat rejection temperature decreases in the vapour power cycle below atmospheric pressure,

a. the vacuum in the condenser also decreases
b. the vacuum in the condenser increases
c. it does not produce any vacuum in condenser
d. none of the above
 Answer  Explanation  Related Ques ANSWER: the vacuum in the condenser increases Explanation: No explanation is available for this question!

30)   What should be the critical temperature of working fluid for maximum efficiency of vapour power cycle?

a. the working fluid should have critical temperature as low as possible
b. the working fluid should have critical temperature as high as possible
c. the critical temperature does not affect the efficiency of the vapour power cycle
d. none of the above
 Answer  Explanation  Related Ques ANSWER: the working fluid should have critical temperature as high as possible Explanation: No explanation is available for this question!

31)   The specific heat of the ideal working fluid used in vapor power cycle

a. should be constant
b. should be large
c. should be small
d. none of the above
 Answer  Explanation  Related Ques ANSWER: should be small Explanation: No explanation is available for this question!

32)   What is the importance of the freezing point of the working fluid in the vapour power cycle?

a. freezing point of working fluid should be below the room temperature
b. freezing point of working fluid should be above the room temperature
c. freezing point of working fluid should be equal to the room temperature
d. does not have any importance
 Answer  Explanation  Related Ques ANSWER: freezing point of working fluid should be below the room temperature Explanation: No explanation is available for this question!

33)   When two vapor cycles are coupled in series and heat rejected by one is absorbed by another, the cycle is called as

a. Dual vapour cycle
b. Binary vapour cycle
c. Coupled vapour cycle
d. none of the above
 Answer  Explanation  Related Ques ANSWER: Binary vapour cycle Explanation: No explanation is available for this question!

34)   In working condition of turbojet engine, velocity of air entering the engine is

a. higher than the velocity of exhaust gases leaving the engine
b. lower than the velocity of exhaust gases leaving the engine
c. equal to the velocity of exhaust gases leaving the engine
d. cannot say
 Answer  Explanation  Related Ques ANSWER: lower than the velocity of exhaust gases leaving the engine Explanation: No explanation is available for this question!

35)   Why do the airplanes fly at higher altitude during the long flights?

a. to avoid collisions as they are at very high speed and controlling will be difficult if something (like towers, hills) comes in the way
b. it is easy to communicate with satellites at high altitudes
c. to save the fuel as air at higher altitude exerts smaller drag force on aircraft
d. none of the above
 Answer  Explanation  Related Ques ANSWER: to save the fuel as air at higher altitude exerts smaller drag force on aircraft Explanation: No explanation is available for this question!

36)   The propulsive power developed by the thrust of engine is given by

a. mair (Vexit – Vinlet)
b. mair (Vexit – Vinlet) × Vaircraft
c. (Vexit – Vinlet) × Vaircraft
d. none of the above
 Answer  Explanation  Related Ques ANSWER: mair (Vexit – Vinlet) × Vaircraft Explanation: No explanation is available for this question!

37)   The propulsive efficiency is the ratio of

a. the propulsive power to the energy input rate
b. the exit velocity rate of exhaust gases to the energy input rate
c. the work done by the turbine to the energy input rate
d. velocity of aircraft to the energy input rate
 Answer  Explanation  Related Ques ANSWER: the propulsive power to the energy input rate Explanation: No explanation is available for this question!

38)   In turbofan engine, fan is used

a. to compress the inlet air more efficiently
b. to increase the total thrust of the engine
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: to increase the total thrust of the engine Explanation: No explanation is available for this question!

39)   In turbofan engine, the bypass ratio is the ratio of

a. total mass flow rate of exhaust stream to the mass flow rate of stream from turbine exhaust
b. total mass flow rate of exhaust stream to the mass flow rate of stream from fan exhaust
c. the mass flow rate of stream from turbine exhaust to the mass flow rate of stream from fan exhaust
d. the mass flow rate of stream from fan exhaust to the mass flow rate of stream from turbine exhaust
 Answer  Explanation  Related Ques ANSWER: the mass flow rate of stream from fan exhaust to the mass flow rate of stream from turbine exhaust Explanation: No explanation is available for this question!

40)   What is the effect of increasing bypass ratio of a turbofan engine on its thrust?

a. thrust increases with increase in bypass ratio of turbofan engine
b. thrust decreases with increase in bypass ratio of turbofan engine
c. thrust of the turbofan engine only depends upon the fuel rate, so no change of thrust with increase in bypass ratio
d. cannot say
 Answer  Explanation  Related Ques ANSWER: thrust increases with increase in bypass ratio of turbofan engine Explanation: No explanation is available for this question!

41)   Heat pump is used

a. to transform low grade rejected heat into high temperature heat source
b. to transform high grade rejected heat into low temperature heat sink
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: to transform low grade rejected heat into high temperature heat source Explanation: No explanation is available for this question!

42)   Which of the following is NOT a type of heat pump?

a. vapour compression type
b. vapour absorption type
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: none of the above Explanation: No explanation is available for this question!

43)   In year-round air conditioning, by reversing refrigerating cycle

a. condenser acts like evaporator
b. evaporator acts like condenser
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!

44)   In gas cycle refrigeration system, the throttle valve of a vapour compression refrigerant system is replaced by

a. capillary tube
b. expander
c. reverse throttle valve
d. none of the above
 Answer  Explanation  Related Ques ANSWER: expander Explanation: No explanation is available for this question!

45)   How much is the temperature drop of real gas by throttling?

a. vary big temperature drop
b. very small temperature drop
c. no temperature drop
d. cannot say
 Answer  Explanation  Related Ques ANSWER: very small temperature drop Explanation: No explanation is available for this question!

46)   The ideal gas-refrigeration cycle is similar to

a. Brayton cycle
b. Reversed Brayton cycle
c. Rankine cycle
d. Reversed Rankine cycle
 Answer  Explanation  Related Ques ANSWER: Reversed Brayton cycle Explanation: No explanation is available for this question!

47)   The horizontal line in psychrometric chart joining the change of state of air represents

a. humidification
b. sensible cooling or heating
c. sensible cooling or heating with humidification
d. sensible cooling or heating with dehumidification
 Answer  Explanation  Related Ques ANSWER: sensible cooling or heating Explanation: No explanation is available for this question!

48)   Air at dry bulb temperature Td1 is passed through the heating coil and some amount of air is by passed unaffected and leaves with dry bulb temperature Tb2 and the temperature of heated air is Td3 (where Td2 < Td3), what is the correct formula for by pass factor (The amount of air by passed unaffected)?

a. Bypass Factor = (Td3 – Td2) / (Td3 – Td1)
b. Bypass Factor = (Td3 – Td1) / (Td3 – Td2)
c. Bypass Factor = (Td2 – Td1) / (Td2 – Td3)
d. Bypass Factor = (Td2 – Td3) / (Td2 – Td1)
 Answer  Explanation  Related Ques ANSWER: Bypass Factor = (Td2 – Td3) / (Td2 – Td1) Explanation: No explanation is available for this question!

49)   Humidification is the process of addition moisture in air at

a. constant wet bulb temperature
b. constant dry bulb temperature
c. constant latent heatn
d. none of the above
 Answer  Explanation  Related Ques ANSWER: constant dry bulb temperature Explanation: No explanation is available for this question!

50)   Which device used to separate condensate from the steam without letting steam escape?

a. condenser
b. steam valve
c. steam trap
d. none of the above
 Answer  Explanation  Related Ques ANSWER: steam trap Explanation: No explanation is available for this question!