# Thermodynamics Test Questions - Set - 5

1)   Macroscopic thermodynamics ______

a. is concerned with the effects of action of many molecules in matter
b. results can be derived from microscopic study of matter
c. is not concerned with the events occurring at the molecular level
d. all of the above
 Answer  Explanation  Related Ques ANSWER: all of the above Explanation: Macroscopic and microscopic are the two point of views through which the behavior of a matter can be studied. In macroscopic point of view, the specific quantity of matter is considered. The behavior of the matter at the molecular level is not considered. In microscopic point of view, the behavior of the matter is described by summing up the behavior of each molecule.

2)   When,
p = specific pressure
v = specific volume
P = Total pressure of gas
V= Total volume of gas
R = Characteristic gas constant
n = number of moles in gas
m = mass of the gas
T = Temperature of the gas
then the ideal gas equation will be

a. v =m R T
b. P V = R T
c. P V = m R T
d. all of the above
 Answer  Explanation  Related Ques ANSWER: P V = m R T Explanation: The pressure–volume –temperature relation of any gas at low pressure is given by,p v = R Twhere R is the universal gas constant and is the molar specific volume, m3/gmol. Dividing it by the molecular weight μ,p v = R Twhere v is the specific volume in, m3/kg and R is the characteristic gas constant.In terms of total volume of gas we can wright this equation as,P V = n R TP V = m R TWhere n is the number of moles and m is mass of gas. This equation is called as ideal gas equation of state.

3)   Which among the following systems undergo/es work transfer?

a. Current flowing through the resistor
b. A shaft rotated by a motor
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: both a. and b. Explanation: When electric current passes through the resistor, work transfer can takes place. This is because the current can drive a motor and the motor can drive a pulley and this can results in lifting a weight.When a shaft is rotated by a system, work transfer can takes place into the system. This is because the shaft can rotate a pulley which can lift a weight. Thus both the systems undergo work transfer.

4)   Which of the following is/are mode/s of storage of internal energy in a system?

a. Macroscopic energy mode
b. Microscopic energy mode
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: both a. and b. Explanation: There are two modes in which energy can be stored in a system, macroscopic energy mode and microscopic energy mode. In macroscopic energy mode, the kinetic energy and the potential energy of a system is considered. Let us consider a fluid element of mass m and a center of mass velocity is V. The macroscopic kinetic energy Ek of the fluid element is,Ek = ½ mV2If this fluid element is elevated to a certain height h from and arbitrary datum, the macroscopic potential energy Ep of the element,Ep = mghThe microscopic energy mode consists of an energy stored in molecular and atomic structure of the system. This energy consists of molecular translational kinetic energy, rotational kinetic energy, vibrational kinetic energy, chemical energy, electrical energy and nuclear energy.If e represents the energy of one molecule then,ε = εtrans + εrot + εvib + εchem + εelectronic + εnuclearand if N is the total number of molecules in the system, the total microscopic internal energy will be,U = NεThus the total internal energy of the system will be,E = Ek + Ep + U

5)   A process of application of breaks in a vehicle is

a. a reversible process
b. an irreversible process
c. a quasi-static process
d. none of the above
 Answer  Explanation  Related Ques ANSWER: an irreversible process Explanation: In the process of application of breaks in a vehicle the kinetic energy of the wheel is transferred to the break flywheel and converted into heat energy. As all of the heat generated is not dissipated in the atmosphere and the internal energy of the flywheel increases. Internal energy exists in the form of kinetic energy (K.E.), potential energy (P.E.) and molecular internal energy (U). Applying balance equation for internal energy,(K.E.)1 + (P.E.)1 + U1 = (K.E.)2 + (P.E.)2 + U2As wheel is taken to rest, (K.E.)2 will be zero and there will be no change in P.E.Therefore,U2 = U1 + (K.E.)1There will be an increase in the molecular internal energy by the absorption kinetic energy of the wheel. The reverse of this process that is the conversion of the increase in the molecular internal energy into the kinetic energy is not possible, therefore the process is irreversible.

6)   A process becomes reversible when

a. it undergoes in the absence of any dissipative effect
b. all the points through the path are at thermodynamic equilibrium
c. it undergoes as a very slow quasi-static process
d. all of the above
 Answer  Explanation  Related Ques ANSWER: all of the above Explanation: A nature processes are irreversible because they contain dissipative effects where work is transformed into an increase in the internal energy of a system. Therefore the conditions of the mechanical, chemical and thermal equilibrium are not satisfied. In reversible process, there is the absence of any dissipative effect. All the work transferred by the system in a process in a single direction can be returned to the system during the reverse process.When a process is carried out through a path on which all the points are thermodynamic equilibrium then this process can also be reversed. These processes are called as quasi-static process. These processes are very slow.

7)   Carnot cycle is

a. a reversible cycle
b. an irreversible cycle
c. practical cycle
d. none of the above
 Answer  Explanation  Related Ques ANSWER: a reversible cycle Explanation: Carnot cycle consists of two reversible isothermal processes and two reversible adiabatic processes. Consider a stationary system as in piston cylinder machine as shown in below diagram,The above Carnot cycle consists ofA reversible isothermal process in which heat Qa enters the system from source A reversibly when cylinder cover is in contact with diathermic cover D.A reversible adiabatic process, in which a diathermic cover D is replaced by the adiabatic cover C and work Wa is done by the system reversibly at the expense of internal energy of the system.A reversible isothermal process, in which again an adiabatic cover C is replaced by a diathermic cover D and heat Qb is rejected to the sink B from the system reversibly.A reversible adiabatic process, in which a diathermic cover D is replaced again by the adiabatic cover C and work Wb is done upon the system reversibly and the internal energy of the system increases.

8)   Which of the following is a reversed heat engine?

a. Heat pump
b. Refrigerator
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: both a. and b. Explanation: In a Carnot heat engine all the processes are reversible. It is possible to reverse the processes in the heat engine individually. When a process is reversed, all the energy transfer associated with the process is reversed but the magnitude of the energy remains same. Heat engine absorbs heat from high temperature reservoir and produces work with the rejection of some amount of heat. If this process is reversed, the reversed heat engine takes heat from low temperature reservoir and rejects heat to a high temperature reservoir with external work is done on the system. This is the called as a heat pump or a refrigerator.

9)   According to the Carnot's theorem, the efficiency of a reversible heat engine operating between a same given constant temperature source and a given constant temperature sink is

a. higher than any other irreversible heat engine
b. less than any other irreversible heat engine
c. equal to any other irreversible heat engine
d. none of the above
 Answer  Explanation  Related Ques ANSWER: higher than any other irreversible heat engine Explanation: The Carnot's theorem states that no other heat engine has a higher efficiency that a reversible engine, when all the heat engines are operated between a given constant temperature source and a given constant temperature sink.Consider the above diagram, the heat engines Ea and Eb are operating between the same constant temperature heat source and constant temperature sink. If heat engine Ea is a reverse heat engine and Eb is any other heat engine then according to the Carnot's theorem the efficiency of Ea is always greater than the efficiency of Eb.

10)   If a reversible heat engine A is operating between the temperature levels T1 and T2 and another reversible heat engine B of different capacity is also operating between the same temperature difference T1 and T2, then the efficiency of reversible heat engine B is

a. greater than efficiency of the reversible heat engine A
b. less than the efficiency of the reversible heat engine A
c. equal to the efficiency of the reversible heat engine A
d. cannot say
 Answer  Explanation  Related Ques ANSWER: equal to the efficiency of the reversible heat engine A Explanation: According to Carnot's theorem, the efficiency of a reversible heat engine operating between a constant temperature heat source and constant temperature sink is always highest among the other heat engines which operate between the same constant temperature heat source and constant temperature sink. Therefore when the two heat engines which are reversible are operating between the same constant temperature heat source and constant temperature sink then both the reversible heat engines have equal efficiency which is highest. This is a corollary of Carnot's theorem. The efficiency of all reversible heat engines operating between the same temperature levels is the same.

11)   Two bodies, initially at temperatures T1 and T2 (T1>T2) have same heat capacity. Suppose a heat engine is operated between these two bodies delivering work. What will be the final temperature (Tf) of the two bodies when after that temperature heat engine will stop working with giving maximum work?

a. Tf = (T1 – T2)
b. Tf = (T1 – T2) / 2
c. Tf = (T1 + T2) / 2
d. Tf = √T1 T2
 Answer  Explanation  Related Ques ANSWER: Tf = √T1 T2 Explanation: No explanation is available for this question!

12)   A body is at a temperature T1 with certain heat capacity and a heat engine is operated between the body and a thermal heat reservoir at temperature (T0). What will be the final temperature of the body when heat engine will stop working?

a. T1
b. T0
c. (T1 + T0) / 2
d. Tf = √T1 T2
 Answer  Explanation  Related Ques ANSWER: T0 Explanation: No explanation is available for this question!

13)   An electric current I is passing through a resistor in contact with a reservoir. The internal energy of the resistor is constant. Heat generated is absorbed by surrounding at temperature T0. What will be the effect on entropy of the universe?

a. Entropy of the universe is always constant
b. The process increases the the entropy of the universe
c. The process decreases the the entropy of the universe
d. cannot say
 Answer  Explanation  Related Ques ANSWER: The process increases the the entropy of the universe Explanation: No explanation is available for this question!

14)   How is heat transfer associated with entropy transfer?

a. the entropy transfer takes places along with heat flow in the direction of heat transfer
b. the entropy transfer takes places along with heat flow in the opposite direction of heat transfer
c. the entropy transfer does not take place along with heat transfer
d. none of the above
 Answer  Explanation  Related Ques ANSWER: the entropy transfer takes places along with heat flow in the direction of heat transfer Explanation: No explanation is available for this question!

15)   What is the entropy transfer associated with work?

a. positive entropy transfer
b. negative entropy transfer
c. no entropy transfer
d. all of the above
 Answer  Explanation  Related Ques ANSWER: no entropy transfer Explanation: No explanation is available for this question!

16)   When system gains entropy from the surrounding, what will be the effect on the molecules of the system?

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

17)   What is the entropy generation?

a. increase in the entropy of a system due to internal irreversibility
b. decrease in the entropy of a system due to internal irreversibility
c. no change in entropy of a system
d. none of the above
 Answer  Explanation  Related Ques ANSWER: increase in the entropy of a system due to internal irreversibility Explanation: No explanation is available for this question!

18)   Which law of thermodynamics expresses that the energy is always conserved quantity wise?

a. First law
b. Second law
c. Third law
d. none of the above
 Answer  Explanation  Related Ques ANSWER: First law Explanation: No explanation is available for this question!

19)   The law of degradation of energy states that

a. the energy is always conserved quantity wise
b. the energy is always conserved quality wise
c. the energy is always degraded quantity wise
d. the energy is always degraded quality wise
 Answer  Explanation  Related Ques ANSWER: the energy is always degraded quality wise Explanation: No explanation is available for this question!

20)   If WR and WI be the work done by a reversible and irreversible processes respectively. In both the processes, system changes between the same end states interacting with the surroundings at pressure p0 and T0. What will be relation between WR and WI?

a. WR = WI
b. WR > WI
c. WR < WI
d. cannot say
 Answer  Explanation  Related Ques ANSWER: WR > WI Explanation: No explanation is available for this question!

21)   The temperature of a substance at which the vapour pressure is equal to 760 mm Hg is called as

a. normal vapour point
b. normal boiling point
c. normal pressure point
d. none of the above
 Answer  Explanation  Related Ques ANSWER: normal boiling point Explanation: No explanation is available for this question!

22)   The temperature at which a pure liquid transforms into vapour at constant pressure is called as

a. vaporisation temperature
b. normal temperature
c. saturation temperature
d. none of the above
 Answer  Explanation  Related Ques ANSWER: saturation temperature Explanation: No explanation is available for this question!

23)   In which condition can real gas closely obey the ideal gas equation?

a. pressure is very small and temperature is very high
b. pressure is very high and temperature is very low
c. both pressure and temperature are very high
d. both pressure and temperature are very low
 Answer  Explanation  Related Ques ANSWER: pressure is very small and temperature is very high Explanation: No explanation is available for this question!

24)   The equation pv=RT is used for ideal gases. The right equation for real gases is van der Waals equation. What is the correct formula for the van der Waals equation?Where
(a/v2)= force of cohesion
b= coefficient related to volume of molecules

a. (p+(a/v2)) (v + b) = RT
b. (p – (a/v2)) (v – b) = RT
c. (p + (a/v2)) (v – b) = RT
d. (p – (a/v2)) (v + b) = RT
 Answer  Explanation  Related Ques ANSWER: (p + (a/v2)) (v – b) = RT Explanation: No explanation is available for this question!

25)   What should be the initial temperature of gas to obtain maximum cooling effect in the Joule-Kelvin expansion?

a. the initial temperature of gas should be less than the temperature corresponding to inversion point of isenthalpic curve of the expansion of gas

b. the initial temperature of gas should be more than the temperature corresponding to inversion point of isenthalpic curve of the expansion of gas

c. the initial temperature of gas should be equal the temperature corresponding to inversion point of isenthalpic curve of the expansion of gas

d. none of the above
 Answer  Explanation  Related Ques ANSWER: the initial temperature of gas should be equal the temperature corresponding to inversion point of isenthalpic curve of the expansion of gas Explanation: No explanation is available for this question!

26)   At the maximum inversion temperature in the graph of isenthalpic or joule-kelvin expansion of a gas, the value of Joule-Kelvin coefficient is

a. negative
b. positive
c. zero
d. positive, negative or zero depends upon initial temperature
 Answer  Explanation  Related Ques ANSWER: zero Explanation: No explanation is available for this question!

27)   What is the effect of reheat on the net work output of the steam power plant?

a. the net work output of the steam power plant decreases with reheat because of the increase in heat addition
b. the net work output of the steam power plant increases
c. the net work output of the steam power plant does not affected by the reheat
d. cannot say
 Answer  Explanation  Related Ques ANSWER: the net work output of the steam power plant increases Explanation: No explanation is available for this question!

28)   The below diagram is the T-s diagram of the Rankine cycle with reheat.
Which process represents the reheat?

a. process 1 – 2
b. process 2 – 2 ′
c. process 2 ′ – 2 ″
d. process 2 – 3 ′
 Answer  Explanation  Related Ques ANSWER: process 2 ′ – 2 ″ Explanation: No explanation is available for this question!

29)   Considering the below T-s diagram of the Rankine cycle with reheat, which condition can improve the efficiency of the cycle slightly?

a. the mean temperature of heat addition in process (1 – 2) should be higher than the mean temperature of heat addition in process (2 ′ – 2 ″)

b. the mean temperature of heat addition in process (2 ′ – 2 ″) should be higher than the mean temperature of heat addition in process (1 – 2)

c. the mean temperature of heat addition in process (2 ′ – 2 ″) should be equal to the mean temperature of heat addition in process (1 – 2)

d. none of the above
 Answer  Explanation  Related Ques ANSWER: the mean temperature of heat addition in process (2 ′ – 2 ″) should be higher than the mean temperature of heat addition in process (1 – 2) Explanation: No explanation is available for this question!

30)   The reheat cycle allows steam power plant

a. to use higher pressure ratio
b. to maintain required quality of steam at the exit of the turbine
c. to increase the turbine work
d. all of the above
 Answer  Explanation  Related Ques ANSWER: all of the above Explanation: No explanation is available for this question!

31)   The mean temperature of heat addition (Tm) in the Rankine cycle can be increased by

a. reheating the steam
b. increasing superheat
c. increasing pressure ratio between which the cycle works
d. all of the above
 Answer  Explanation  Related Ques ANSWER: all of the above Explanation: No explanation is available for this question!

32)   In ideal regenerative cycle (saturated steam Rankine cycle), the heat addition takes place

a. from lowest temperature to highest temperature
b. at constant pressure
c. at constant temperature
d. none of the above
 Answer  Explanation  Related Ques ANSWER: at constant temperature Explanation: No explanation is available for this question!

33)   What is the relation between efficiencies of the ideal regenerative Rankine cycle and the Carnot cycle?

a. the efficiency of ideal regenerative Rankine cycle is less than the efficiency of Carnot cycle
b. the efficiency of ideal regenerative Rankine cycle is more than the efficiency of Carnot cycle
c. the efficiency of ideal regenerative Rankine cycle is equal to the efficiency of Carnot cycle
d. none of the above
 Answer  Explanation  Related Ques ANSWER: the efficiency of ideal regenerative Rankine cycle is equal to the efficiency of Carnot cycle Explanation: No explanation is available for this question!

34)   Which cycle is more suitable for the reciprocating engines?

a. Brayton cycle
b. Rankine cycle
c. Otto cycle
d. All of the above are similarly efficient for same capacity
 Answer  Explanation  Related Ques ANSWER: Otto cycle Explanation: No explanation is available for this question!

35)   Which cycle is more efficient for electricity generation plant?

a. Brayton cycle
b. Rankine cycle
c. Otto cycle
d. none of the above
 Answer  Explanation  Related Ques ANSWER: Rankine cycle Explanation: No explanation is available for this question!

36)   Which among the following is the basic air standard cycle for all modern gas turbine plants?

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

37)   What is the effectiveness of the regenerator in gas power plant?

a. ratio of actual rise in temperature of air to the maximum possible rise in temperature of air
b. ratio of the maximum possible rise in temperature of air to actual rise in temperature of air
c. difference between maximum possible rise in temperature of air and actual rise in temperature of air
d. none of the above
 Answer  Explanation  Related Ques ANSWER: ratio of actual rise in temperature of air to the maximum possible rise in temperature of air Explanation: No explanation is available for this question!

38)   What is the effect of regeneration on mean temperature of heat addition in Brayton cycle?

a. mean temperature of heat addition decreases because of regeneration
b. mean temperature of heat addition increases because of regeneration
c. mean temperature of heat addition is not affected by use of regenerator
d. none of the above
 Answer  Explanation  Related Ques ANSWER: mean temperature of heat addition increases because of regeneration Explanation: No explanation is available for this question!

39)   What is the effect of regeneration on net work output in Brayton cycle?

a. net work output decreases because of regeneration
b. net work output increases because of regeneration
c. net work output is not affected by use of regenerator
d. none of the above
 Answer  Explanation  Related Ques ANSWER: net work output is not affected by use of regenerator Explanation: No explanation is available for this question!

40)   If pressure ratio in Brayton cycle increases

a. the efficiency of the cycle increases
b. the efficiency of the cycle decreases
c. there is no any effect on the efficiency of the cycle
d. cannot say
 Answer  Explanation  Related Ques ANSWER: the efficiency of the cycle increases Explanation: No explanation is available for this question!

41)   What is the disadvantage of ammonia using as a refrigerant?

a. ammonia cannot be detected in case of leakage
b. ammonia has a bad effect on ozone layer
c. ammonia is toxic in nature
d. ammonia has higher energy cost
 Answer  Explanation  Related Ques ANSWER: ammonia is toxic in nature Explanation: No explanation is available for this question!

42)   The mechanical work required to run vapour absorption system

a. is more than the mechanical work required to run vapour compression system
b. is less than the mechanical work required to run vapour compression system
c. is similar to the mechanical work required to run vapour compression system
d. cannot say
 Answer  Explanation  Related Ques ANSWER: is less than the mechanical work required to run vapour compression system Explanation: No explanation is available for this question!

43)   The compressor in the vapour compression system is replaced by

a. an absorber
b. a generator
c. an absorber-generator
d. none of the above
 Answer  Explanation  Related Ques ANSWER: an absorber-generator Explanation: No explanation is available for this question!

44)   What is the condition of refrigerant at the exit of evaporator in aqua-ammonia absorption system?

a. low pressure ammonia vapour
b. high pressure ammonia vapour
c. low pressure strong vapour mixture of ammonia and water
d. high pressure strong vapour mixture of ammonia and water
 Answer  Explanation  Related Ques ANSWER: low pressure ammonia vapour Explanation: No explanation is available for this question!

45)   What is the process carried out in generator of vapour absorption refrigeration cycle?

a. weak solution of ammonia in water is heated
b. strong solution of ammonia in water is heated
c. only water is heated and heat is given to the ammonia to form its vapour
d. none of the above
 Answer  Explanation  Related Ques ANSWER: strong solution of ammonia in water is heated Explanation: No explanation is available for this question!

46)   In absorber of aqua-ammonia absorption refrigeration system

a. strong solution is taken in and weak solution is given out
b. weak solution is taken in and strong solution is given out
c. the ammonia vapour from strong solution is taken out and made it a weak solution
d. none of the above
 Answer  Explanation  Related Ques ANSWER: weak solution is taken in and strong solution is given out Explanation: No explanation is available for this question!

47)   The temperature, at which the air cannot hold all the water vapour mixed in it and some vapour starts condensing, is called as

a. humidification temperature
b. dehumidification temperature
c. dew point temperature
d. none of the above
 Answer  Explanation  Related Ques ANSWER: dew point temperature Explanation: No explanation is available for this question!

48)   The formation of fog starts when,

a. air temperature is equal to the dew point temperature
b. air temperature is greater than the dew point temperature
c. both a. and b.
d. none of the above
 Answer  Explanation  Related Ques ANSWER: air temperature is equal to the dew point temperature Explanation: No explanation is available for this question!

49)   When the dew point temperature is equal to the air temperature then the relative humidity is

a. 0%
b. 50%
c. 100%
d. unpredictable
 Answer  Explanation  Related Ques ANSWER: 100% Explanation: No explanation is available for this question!

50)   The purpose of superheater in a boiler is

a. to increase the temperature of saturated steam with increase in its pressure
b. to increase the temperature of saturated steam without increase in its pressure
c. to increase the temperature of feedwater for better efficiency
d. none of the above
 Answer  Explanation  Related Ques ANSWER: to increase the temperature of saturated steam without increase in its pressure Explanation: No explanation is available for this question!