# Thermodynamics - Mechanical Engineering test questions

## Thermodynamics - Mechanical Engineering test questions

1) Which of the following is an intensive property of a thermodynamic system?

a) Mass
b) Temperature
c) Energy
d) Volume

2) The absolute zero pressure will be

a) At a temperature of -273 K
b) At sea level
c) When molecular momentum of the system becomes zero
d) Under vacuum conditions
e) All of the above

ANSWER: c) When molecular momentum of the system becomes zero

3) Which of the following statement is true?

a) Boiling point of water decreases with increasing pressure
b) Freezing temperature of water decreases with increasing pressure
c) Specific volume of water decreases on freezing
d) All of the above

ANSWER: b) Freezing temperature of water decreases with increasing pressure

4) Which of the following statement is true?

a) The slope of vaporisation curve is always positive
b) The slope of fusion curve is positive for all pure substances
c) The slope of sublimation curve is negative for all pure substances
d) The slope of vaporisation curve is always negative

ANSWER: d) The slope of vaporisation curve is always negative

5) At critical point the latent heat of vaporisation is

a) Greater than zero
b) Equal to zero
c) Less than zero
d) None of the above

6) What will happen when the pressure of feed water is increased?

a) Boiling point of water decreases and enthalpy of evaporation increases
b) Boiling point of water increases and enthalpy of evaporation decreases
c) Boiling point of water increases and enthalpy of evaporation increases
d) None of these

ANSWER: b) Boiling point of water increases and enthalpy of evaporation decreases

7) For which of the following instances the throttling calorimeter can be used alone.

a) Very low dryness fraction upto 0.7
b) Dryness fraction of only low pressure steam
c) High dryness fraction upto 0.98
d) Throttling calorimeter cannot be used alone

ANSWER: c) High dryness fraction upto 0.98

8) In throttling process

a) h12 = h2
b) h1 = h2
c) h1 = h2 hfg/Ts
d) h2 = h1 + hfg/Ts

9) An isentropic process is always:

b) Frictionless.
c) Reversible and isothermal.

10) Among the following which is not property of the system?

a) Pressure.
b) Temperature.
c) Heat.
d) Specific volume.

11) In isothermal process:

a) Change in internal energy is zero.
b) Pressure remains constant.
c) Volume remains constant.
d) Enthalpy change is maximum.

ANSWER: a) Change in internal energy is zero.

12) What do the second law of thermodynamics defines?

a) Heat.
b) Work.
c) Entropy.
d) Internal energy.

13) The efficiency of the Carnot engine …………………., if the temperature of the source is increased.

a) Does not change.
b) Increases.
c) Decreases.
d) Depends on other factors.

14) On what does the efficiency of an ideal Carnot engine depends?

a) The working substance.
b) The construction of engine.
c) The temperature of the sink only.
d) The temperatures of both the source and the sink.

ANSWER: d) The temperatures of both the source and the sink.

15) Kelvin – Planck’s law deals with:

a) Conservation of heat.
b) Conservation of energy.
c) Conversion of work into heat.
d) Conversion of heat into work.

ANSWER: d) Conversion of heat into work.

16) For saturated air:

a) Wet bulb depression is negative.
b) Wet bulb depression can be either positive or negative.
c) Wet bulb depression is positive.
d) Wet bulb depression is zero.

ANSWER: d) Wet bulb depression is zero.

17) Enthalpy ………………….. during sensible heating of moist air.

a) Increases.
b) Decreases.
c) Remains constant.
d) None of the above.

18) Which among the following statement is correct?

a) Evaporative cooling is a cooling and humidification process.
b) Evaporative cooling is a cooling and dehumidification process.
c) Evaporative cooling and sensible cooling is the same.
d) Evaporative cooling is not effective for hot and dry climates.

ANSWER: a) Evaporative cooling is a cooling and humidification process.

19) What does Orsat apparatus gives?

a) Volumetric analysis of products of combustion including H2O.
b) Gravimetric analysis of products of combustion including H2O.
c) Gravimetric analysis of the dry products of combustion.
d) Volumetric analysis of the dry products of combustion.

ANSWER: d) Volumetric analysis of the dry products of combustion.

20) Bomb calorimeter is used to find the calorific value of ……………… fuels.

a) Solid.
b) Gaseous.
c) Solid and gaseous.
d) None of the above.

21) Rankine cycle operating on low pressure limit of p1 and high pressure limit p2:

a) May be more or less depending upon the magnitudes of p1 and p2.
b) Has lower thermal efficiency than Carnot cycle operating between same pressure limit.
c) Has same thermal efficiency as Carnot cycle operating between same pressure limits.
d) Has higher thermal efficiency than the Carnot cycle operating between same pressure limits.

ANSWER: d) Has higher thermal efficiency than the Carnot cycle operating between same pressure limits.

22) What does Rankine cycle comprises of?

a) Two isothermal processes and two constant pressure processes.
b) Two isentropic processes and two constant pressure processes.
c) Two isentropic processes and two volume pressure processes.
d) None of the above.

ANSWER: b) Two isentropic processes and two constant pressure processes.

23) The maximum percentage gain in thermal efficiency of regenerative feed heating cycle

a) Remains same unaffected by number of feed heaters.
b) Decreases with number of feed heaters increasing.
c) Increases with number of feed heaters increasing.
d) None of the above.

ANSWER: c) Increases with number of feed heaters increasing.

24) How is the thermal efficiency of a gas turbine plant as compared to diesel engine plant?

a) Lower.
b) Higher.
c) Same.
d) None of these.

25) For theoretical Otto cycle the work output

a) Increases with increase in pressure ratio.
b) Increases with increase in compression ratio.
c) Increases with increase in adiabatic index ?.
d) Follows all of the above.

ANSWER: d) Follows all of the above.

26) For same compression ratio

a) Thermal efficiency of Otto cycle cannot be predicted.
b) Thermal efficiency of Otto cycle is same as that for diesel cycle.
c) Thermal efficiency of Otto cycle is less than that of diesel cycle.
d) Thermal efficiency of Otto cycle is greater than that of diesel cycle.

ANSWER: d) Thermal efficiency of Otto cycle is greater than that of diesel cycle.

27) Greater the difference between jet velocity and aeroplane velocity

a) Greater is the propulsive efficiency.
b) Less is the propulsive efficiency.
c) Unaffected is the propulsive efficiency.
d) None of these.

ANSWER: c) Unaffected is the propulsive efficiency.

28) If the cut-off is decreased the efficiency of diesel cycle

a) Increases.
b) Decreases.
c) Remains unchanged.
d) Any of the above.

29) First law of thermodynamics deals with conservation of

a) Momentum.
b) Mass.
c) Energy.
d) Heat.

30) For any thermodynamic process the area under the T-s diagram represents

a) Heat absorbed only.
b) Heat rejected only.
c) Work done during the process.
d) Heat absorbed or rejected.

ANSWER: d) Heat absorbed or rejected.

31) The external work done is not equal to zero in

a) Throttling.
b) Free expansion.
c) Constant volume process.
d) Constant pressure process

32) The extension and compression of a helical spring is an example of

a) Isothermal process.
b) Reversible process.
c) Irreversible process.

33) Entropy of universe

a) Tends to a minimum.
b) Tends to a maximum.
c) Tends to zero.
d) None of the above.

ANSWER: b) Tends to a maximum.

34) Cetane number of a diesel fuel is a measure of its ………………..

a) Delay period.
b) Viscosity.
c) Volatility.
d) Ignition quality.

35) The work done is equal to the change in internal energy of a gas for

b) Isothermal process.
c) Constant volume process.
d) Constant pressure process.

36) What will the same volume of all gases represent?

a) Specific gravity.
b) Densities.
c) Specific weights.
d) Molecular weights.

37) Universal gas constant is defined as the product of the molecular weight of the gas and

a) Gas constant.
b) Specific heat at constant volume.
c) Specific heat at constant pressure.
d) Ratio of two specific heats.

38) During a throttling process

a) Exchange of heat does not take place.
b) Expanding steam does no work.
c) Internal energy of steam does not change.
d) All of the above.

ANSWER: d) All of the above.

39) A Bell – Coleman cycle is a reversed ……………….cycle.

a) Brayton.
b) Otto.
c) Joule.
d) Carnot.

40) All gases behave ideally under which of the following conditions?

a) High pressure conditions.
b) Low pressure conditions.
c) Vacuum conditions.
d) All of these.

41) Which among the following statement is incorrect for calculating air standard efficiency?

a) Gases dissociate at higher temperatures.
b) Working substance is perfect gas.
c) All processes are reversible.
d) Specific heat remains constant at all temperatures.

ANSWER: a) Gases dissociate at higher temperatures.

42) Theoretically, a petrol engines operates on …………..cycle.

a) Constant entropy.
b) Constant pressure.
c) Constant volume.
d) Constant temperature.

43) ………………is the unit of entropy.

a) J/Kg
b) J/Kg K
c) J/K
d) J/Kgs

44) Resultant entropy of the system will …………….when two gases suddenly mix up with each other.

a) Remain unaltered.
b) Decrease.
c) Increase.
d) Become zero.

45) For any irreversible process the net entropy change is

a) Unity.
b) Infinite.
c) Negative.
d) Positive.

46) Internal energy and enthalpy of an ideal gas are functions of

a) Temperature only
b) Pressure only
c) Specific volume only
d) Temperature and pressure

47) For real gases, cp will be equal to cv

a) At triple point
b) At critical temperature
c) At absolute zero
d) Above critical temperature

#### Discussion

• RE: Thermodynamics - Mechanical Engineering test questions -vishal (12/18/15)
• good questions
• RE: Thermodynamics - Mechanical Engineering test questions -Gopabandhu pradhan (12/11/15)
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• RE: Thermodynamics - Mechanical Engineering test questions -vivek kumar (10/20/15)
• really a collection of good questions
• RE: Thermodynamics - Mechanical Engineering test questions -arun pratap singh (08/27/15)
• ques9.
there is one more case where process is isentropic when internal irreversibilities are compensated by Q/T .
so its not true that isentropic process is always reversible adiabatic.
source- p.k nag thermo
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