# Thermodynamics mcqs with answers pdf

## SPPU Thermodynamics mcq

Q. 1. The water tubes in a simple vertical boiler are

A : Horizontal
B : Vertical
C : Inclined
D : All of the above

Inclined

Q. 2. When water is heated without rise of temperature, it consumes

A : Latent heat
B : Enthalpy
C : Sensible heat
D : None

Latent heat

Q. 3. Cochran boiler is a……

A : Horizontal fire tube boiler
B : Horizontal water tube boiler
C : Vertical water tube type
D : Vertical fire tube type

Vertical fire tube type

Q. 4. Availability function is expressed as

A : a = (u + p0v – T0s)
B : a = (u + p0dv + T0ds)
C : a = (du + p0dv – T0ds)
D : a = (u + p0v + T0s).

a = (u + p0v – T0s)

Q. 5. Specific heat at constant pressure and at constant volume for real gases

A : Remain the same always
B : Keep on changing as the temperature changes
C : Cp < Cv always D : Both B & C are true

Keep on changing as the temperature changes

Q. 6. Otto cycle is the air standard cycle of

A : spark ignition (SI) engine
B : compression (CI) ignition engine
C : both SI and CI engines
D : None of above

spark ignition (SI) engine

Q. 7. Open system

A : Can exchange both mass and energy
B : Can exchange only mass
C : Can exchange only energy
D : Cannot exchange either mass or energy

Q. 7. Open system

A : Can exchange both mass and energy
B : Can exchange only mass
C : Can exchange only energy
D : Cannot exchange either mass or energy

Q. 8. For a constant pressure process

A : Work done is maximum and no heat is transferred
B : Work done is minimum and heat transferred is maximum
C : Work done is zero and Heat added is equal to the change in the internal energy of
the system
D : Heat added to the system is equal to the change in Enthalpy of the fluid

Heat added to the system is equal to the change in Enthalpy of the fluid

Q. 9. If the system converts all heat into work such a device is

A : PMM-1
B : PMM-2
C : PMM-3
D : None

PMM-2

Q. 10. The ratio of actual mass of water vapour in a given volume of moist air to
the mass of water vapour in the same volume of saturated air at the same
temperature and pressure, is called

A : Humidity ratio
B : Absolute humidity
C : Relative humidity
D : Degree of saturation

Relative humidity

Q. 11. What is the relative humidity for a saturated air?

A : 0
B : 0.5
C : 1
D : cannot say

1

Q. 12. Which ideal process is carried out at the turbine in vapour power cycle?

C : reversible constant pressure heat addition
D : reversible constant pressure heat rejection

Q. 13. What is the exergy of a system?

A : The minimum work that can be extracted from a system till it reaches
thermodynamic equilibrium with its surroundings
B : The maximum work that can be extracted from a system till it reaches
thermodynamic equilibrium with its surroundings
C : The maximum entropy that can be increased in a system till it reaches
thermodynamic equilibrium with its surroundings
D : none of the above

The maximum work that can be extracted from a system till it reaches thermodynamic equilibrium with its surroundings

Q. 14. The thermal efficiency of theoretical Otto cycle

A : increases with increase in compression ratio
B : increases with increase in isentropic index γ
C : does not depend upon the pressure ratio
D : follows all the above.

follows all the above.

Q. 15. During heating and dehumidification process, dry bulb temperature

A : Remains constant
B : Increases
C : Decreases
D : None of these

Increases

Q. 16. The Brayton cycle is the air standard cycle for

A : gas turbine power plant
B : SI engine
C : CI engine
D : none of the above

gas turbine power plant

Q. 17. How is the heat added in the Otto cycle?

A : reversibly at constant pressure
B : irreversibly at constant pressure
C : reversibly at constant volume
D : irreversibly at constant volume

reversibly at constant volume

Q. 18. The draught in locomotive boilers is produced by a ……..

A : Chimney
B : Centrifugal fan
C : Steam jet
D : All of the above

Steam jet

Q. 19. In diesel engine, the fuel is ignited by

A : spark
B : injected fuel
C : heat resulting from compressing air that is supplied for combustion
D : ignitor

heat resulting from compressing air that is supplied for combustion

Q. 20. Dry bulb temperature is the temperature of air recorded by a
thermometer, when

A : It is not affected by the moisture present in the air
B : Its bulb is surrounded by a wet cloth exposed to the air
C : The moisture present in it begins to condense
D : None of the above

It is not affected by the moisture present in the air

Q. 21. In vapour refrigeration cycle, which of the following is used for
expansion?

A : expansion engine
B : throttling valve or capillary tube
C : Turbine
D : all of the above

throttling valve or capillary tube

Q. 22. How is the heat added in the Diesel cycle?

A : reversibly at constant pressure
B : irreversibly at constant pressure
C : reversibly at constant volume
D : irreversibly at constant volume

reversibly at constant pressure

Q. 23. Second Law is the law of

A : Thermal equilibrium
B : Thermodynamic equilibrium
C : Law of entropy generation
D : Conservation of energy principle

Law of entropy generation

Q. 24. Which of the folling is a water tube boiler……..

A : Locomotive boiler
B : Lancashire boiler
C : Cornish boiler
D : Babcock and wilcox boiler

Babcock and wilcox boiler

Q. 25. The change in enthalpy in closed system is equal to the heat transferred
if the reversible process occurs at constant

A : Pressure
B : Volume
C : Temperature
D : Entropy

Pressure

Q. 26. The compression ratio is the ratio of ____________

A : Swept volume to total volume
B : Total volume to swept volume
C : Total volume to clearance volume
D : None of the mentioned

Swept volume to total volume

Q. 27. The amount of heat transferred to convert unit mass of solid to vapour
or vice versa is called as

A : latent heat of vaporization
B : latent heat of evaporation
C : latent heat of sublimation
D : specific heat

latent heat of sublimation

Q. 28. The difference between dry bulb temperature and wet bulb temperature,
is called

A : Dry bulb depression
B : Wet bulb depression
C : Dew point depression
D : Degree of saturation

Wet bulb depression

Q. 29. Carnot cycle consists of……..

A : Two constant volume and two reversible adibatic processes
B : Two isothermal and two reversible adibatic processes
C : Two constant pressure and two reversible adibatic processes
D : One constant volume,one constant pressure and two reversible adibatic processes

Two isothermal and two reversible adibatic processes

Q. 30. The air standard Otto cycle comprises

A : two constant pressure processes and two constant volume processes
B : two constant pressure and two constant entropy processes
C : two constant volume processes and two constant entropy processes
D : none of the above.

two constant volume processes and two constant entropy processes

Q. 31. In a spray washing system, if the temperature of water is higher than the
dry bulb temperature of entering air, then the air is

A : Heated and dehumidified
B : Heated and humidified
C : Cooled and humidified
D : Cooled and dehumidified

Heated and humidified

Q. 32. What is the maximum content of moisture allowed at the turbine
exhaust in the steam power plant?

A : 0.5
B : 0.6
C : 0.3
D : 0.15

0.15

Q. 33. The wet bulb temperature at 100% relative humidity is ________ dew point
temperature.

A : Same as
B : Lower than
C : Higher than
D : None of these

Same as

Q. 34. COP of a heat pump,

A : Would always be less than 1
B : Would always be greater than 1
C : Data insufficient
D : None of the above

Would always be greater than 1

Q. 35. A compressor, refrigerator, pump, air conditioner are a

A : Work producing device
B : Work absorbing device
C : Both A &B are correct
D : Both A &B are incorrect

Work absorbing device

Q. 36. When dry bulb temperature (DBT) and wet bulb temperature (WBT) are
measured, greater the difference between DBT and WBT,

A : greater the amount of water vapour held in the mixture
B : smaller the amount of water vapour held in the mixture
C : same the amount of water vapour held in the mixture
D : none of the above

smaller the amount of water vapour held in the mixture

Q. 37. The dryness (x) fraction of superheated steam is taken as

A : x= 0
B : x= 0.75
C : x= 0.9
D : x= 1

x= 1

Q. 38. The comfort conditions in air conditioning are at (where DBT = Dry bulb
temperature, and RH = Relative humidity)

A : 25°C DBT and 100% RH
B : 20°C DBT and 80% RH
C : 22°C DBT and 60% RH
D : 25°C DBT and 40% RH

22°C DBT and 60% RH

Q. 39. Lost work is given by

A : pdV-dW
B : pdV+dW
C : -pdV-dW
D : pdV*dW

pdV-dW

Q. 40. The specific humidity during heating and humidification process.

A : Remains constant
B : Increases
C : Decreases
D : None of these

Increases

Q. 41. 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

freezing point of working fluid should be below the room temperature

Q. 42. The efficiency of the Otto cycle is independent of

A : Heat supplied
B : Compression ratio
C : Ratio of specific heats
D : None of the above

Heat supplied

Q. 43. First applied to Turbine is

A : Q=(H2-H1)
B : Q=(H1-H2)
C : W=(H2-H1)
D : W=(H1-H2)

W=(H1-H2)

Q. 44. What is the state, at which saturated liquid line with respect to
vaporisation and saturated vapour line on p-v diagram of pure substance, meet
called?

A : saturation state
B : critical state
C : vaporisation state
D : superheated vapour state

critical state

Q. 45. The internal energy of saturated water at the triple point is

A : equal to 1
B : equal to 0
C : equal to minus 1
D : infinity

equal to 0

Q. 46. 1 bar gauge is = ——- bar absolute

A : 213
B : 313
C : 413
D : 0

213

Q. 47. For any irreversible process the net entropy change is

A : standard temperature conditions
B : constant volume
C : constant pressure
D : constant temperature

constant temperature

Q. 48. The function of a steam trap is to

A : Lift the steam
B : Separate the steam
C : Discharge the condesate
D : Heat the steam

Discharge the condesate

Q. 49. The cycle which consists of two reversible adiabatic processes and two
reversible isobaric processess is called as

A : Rankine cycle
B : Carnot cycle
C : Brayton cycle
D : Ericsson cycle

Brayton cycle

Q. 50. Which of the following statement is correct?

A : The human body can lose heat even if its temperature is less than the atmospheric
temperature.
B : The increase in air movement increases the evaporation from the human body.
C : The warm air increases the rate of radiation of heat from the human body.
D : Both (A) and (B)

Both (A) and (B)

Q. 51. For unsaturated air, the dew point temperature is __________ wet bulb
temperature.

A : Equal to
B : Less than
C : More than
D : None of these

Less than

Q. 52. Total entropy change of the ice as it melts into water

A : 1.495 KJ/K
B : 1.5549 KJ/K
C : 1.649 KJ/K
D : 1.749 KJ/K

1.5549 KJ/K

Q. 53. Enthalpy of the steam at the entry of the condenser is 200 kJ Enthalpy of
the water at the exit of the condenser is 100 kJ. What will be the work done by the
condenser

A : 0 kJ
B : 300 kJ
C : 200 kJ
D : None of the above

0 kJ

Q. 54. Rankine efficiency of a steam power plant

A : improves in summer as compared to that in winter
B : improves in winter as compared to that in summer
C : is unaffected by climatic conditions
D : none of the above.

improves in winter as compared to that in summer

Q. 55. If the COP of a refrigerator is 2.5, COP of the heat pump would be,

A : 3.5
B : 1.5
C : 2.5
D : 4.5

3.5

Q. 56. The dry bulb temperature lines, on the psychrometric chart are

A : Vertical and uniformly spaced
B : Horizontal and uniformly spaced
C : Horizontal and non-uniformly spaced
D : Curved lines

Vertical and uniformly spaced

Q. 57. As relative humidity decreases, the dew point temperature will be
________ wet bulb temperature.

A : Same as
B : Lower than
C : Higher than
D : None of these

Lower than

Q. 58. To be sure that steam after throttling is in the single-phase or
superheated vapour, a minimum of ____ is desired.

A : 10 degree Celsius
B : -5 degree Celsius
C : 0 degree Celsius
D : 5 degree Celsius

5 degree Celsius

Q. 59. In air standard Diesel cycle, at fixed compression ratio and fixed value of

A : thermal efficiency increases with increase in heat addition cut-off ratio
B : thermal efficiency decreases with increase in heat addition cut-off ratio
C : thermal efficiency remains same with increase in heat addition cut-off ratio
D : none of the above.

thermal efficiency decreases with increase in heat addition cut-off ratio

Q. 60. Specific internal energy of dry steam is given by

A : u= hg + 100 p Vg
B : u = hg – 100 p Vg
C : u = 100 hg/p Vg
D : None