Multiple choice questions (MCQ) on Thermodynamics

By | June 26, 2013

1. According to first law of thermodynamics

a. Total internal energy of a system during a process remains constant

b. Total energy of a system remains constant

c. Work done by a system is equal to the heat transferred by the system

d. None of the above


2. The measurement of a thermodynamics property known as temperature is based on

a. Zeroth law of thermodynamics           b. First law of thermodynamics

c. Second law of thermodynamics         d. None of the above


3. Which of the following is correct?

a. Absolute pressure = Gauge pressure + Atmospheric pressure

b. Gauge pressure = Absolute pressure + Atmospheric pressure

c. Atmospheric pressure = Gauge pressure + Absolute pressure

d. None of the above


4. A mixture of gas expands from 0.03m3 to 0.06m3 at a constant pressure of 1 MPa and absorbs 84 k J of heat during the process. The change in internal energy of the mixture is

a. 30 k J           b. 54 k J           c. 84 k J           d. None of the above


5. For the constant pressure and heat input, the air standard efficiency of gas power cycle is in the order

a. Dual cycle, Diesel cycle, Otto cycle    b. Otto cycle, Diesel cycle, Dual cycle

c. Dual cycle, Otto cycle, Diesel cycle    d. None of the above


6. An open cycle gas turbine works on

a. Carnot cycle              b. Otto cycle     c. Joule’s cycle             d. None of the above


7. The efficiency of the dual combustion cycle for the same compression ratio, is____diesel cycle.

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


8. Reheating in a gas turbine

a. Increase the thermal efficiency           b. Increase the turbine work

c. Decreases the thermal efficiency        d. None of the above


9. The purpose of governing in steam turbine is to

a. Maintain the speed of turbine                         b. Reduce the efficiency of heat pump

c. Reheat the steam and improves its quality      d. None of the above


10. Blade efficiency is also known as

a. Stage efficiency                    b. Diagram efficiency

c. Nozzle efficiency                   d. None of the above


11. The heating of gas at constant volume is governed by

a. Boyle’s law                            b. Charle’s law

c. Gay Lussac law                     d. None of the above


12. A regenerative steam cycle renders

a. Decreased work output per unit mass

b. Steam as well as increase thermal efficiency

c. Decreased work output per unit mass of system

d. None of the above


13. The impulse reaction turbine has its driving force

a. As an impulsive force            b. As a reaction force

c. Partly as impulsive force and partly as reaction force

d. None of the above


14. A process in which the working substance neither receives nor gives heat to its surroundings during expansion or compression is called

a. Isothermal process                b. Hyperbolic process

c. Adiabatic process                 d. None of the above


15. The mean effective pressure of a diesel engine with fixed compression ratio can be improved by

a. Increasing back pressure                   b. Increasing cut off ratio

c. Increasing operating speed                d. None of the above


16. Carnot cycle has maximum efficiency for

a. Diesel engine                                    b. Petrol engine

c. Reversible engine                  d. None of the above


17. In Carnot cycle heat is rejected at constant

a. Pressure       b. Temperature  c. Volume         d. None of the above


18. The expansion ratio is the ratio of (where v1 is the volume at the beginning of expansion and v2 is the volume at the end of expansion).

a. v1/v2              b. v2/v1              c. (v1+v2)/v1                   d. None of the above


19. Air standard efficiency is equal to

a. (Heat supplied + Heat rejected) / Heat rejected

b. Heat rejected / (Heat rejected + Heat supplied)

c. (Heat supplied + Heat rejected) / Heat supplied

d. None of the above


20. 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 above


21. Identify the process of change of a close system in which the work transfer is maximum.

a. Isothermal                 b. Isochoric                   c. Isentropic                  d. Polytropic


22. A gas turbine cycle with infinitely large number of stages during compression and expansion approaches

a. Stirling cycle             b. Atkinson cycle          c. Ericsson cycle           d. Brayton cycle


23. The COP of a refrigerator on a reversed Carnot cycle is 5. The ratio of higher absolute temperature to the lower temperature (i.e. T2/T1) is

a. 1.25                          b. 1.3                            c. 1.4                            d. 1.2


24. For a non-flow constant pressure process the heat exchange is equal to

a. zero                                                  b. the work done

c. the change in internal energy              d. the change in enthalpy


25. A higher value of Vander Waal’s constant for a gas indicates that the

a. molecules of the gas have smaller diameter                b. gas can be easily liquefied

c. gas has higher molecular weight                                 d. gas has lower molecular weight


26. In which one of the following processes is there an increase in entropy with no degradation of energy?

a. Polytropic expansion             b. Isothermal expansion

c. Isochoric heat addition           d. Isobaric heat addition


27. In a convergent-divergent nozzle, normal shock can generally occur

a. along divergent portion and throat                  b. along the convergent portion

c. anywhere along the length                              d. near the inlet


28. In an adiabatic process, 5000J of work is performed on a system. The system returns to its original state while 1000J of heat is added. The work done during the non-adiabatic process is

a. +4000J                      b. -4000J                      c. +6000J                      d. -6000J


29. For a reversible power cycle, the operating temperature limits are 800 K and 300 K. It takes 400 kJ of heat. The unavailable work will be

a. 250kJ            b. 150kJ           c. 120kJ            d. 100kJ


30. The heat transferred in a thermodynamic cycle of a system consisting of four processes are successively 0, 8 , 6 and -4 units. The net change in the internal energy of the system will be

a. -8                  b. zero              c. 10                 d. -10