Objective questions in mechanical engineering (Thermal Engineering) for competitive exams

6. During the throttling process
(A) Internal energy does not change
(B) Pressure does not change
(C) Entropy does not change
(D) Enthalpy does not change

7. The cycle generally used for gas turbines is 
(A) Rankine cycle
(B) Brayton cycle
(C) Dual cycle
(D) Carnot cycle

8. At the critical point, the enthalpy of vaporization is
(A) Only dependent on temperature
(B) Zero
(C) Minimum
(D) Maximum

9. The process during which external work is done is not zero, 
(A) Constant volume process
(B) Constant pressure process
(C) Throttling
(D) Free Expansion

10. The efficiency of a diesel cycle will be maximum when 
(A) Speed is high
(B) Injection pressure is high
(C) Cylinder is water-cooled
(D) Cut off is zero

11. A reversible engine working between temperature limits of 500 K and 1000 K received 50 kJ of heat. The work done by the engine will be 
(A) 50 kJ
(B) 25 kJ
(C) -25 kJ
(D) 100 kJ

12. The function of a condenser in a steam power plant is 
(A) to reduce back pressure
(B) to utilize the heat of exhaust steam
(C) to preheat feed water with exhaust steam
(D) to act as a heat sink

13. 1 Torr is equal to 
(A) 1 mm Hg
(B) 13.6 cm of water column
(C) 760 mm of Hg
(D) 760 mm of Water

14. The negative loop in the PV diagrams of a petrol engine is due to 
(A) Pre-ignition
(B) Detonation
(C) Suction of air
(D) Early opening of the exhaust valve

15. In the case of a white body, absorptivity is 
(A) Zero
(B) Between 0 and 0.5
(C) More than 0.5
(D) 1

16. Solar cells are made of
(A) Steel
(B) Silica
(C) Antimony
(D) Phosphorus

17. A newly charged ammonia compression system, the clicking sound in the expansion valve indicates
(A) Evaporator coils chocked
(B) Excessive ammonia charged
(C) High pressure after compression
(D) Lack of ammonia

18. In a vapor absorption system the function of the rectifier is 
(A) To separate ammonia and water
(B) To cool the vapor leaving the analyzer
(C) To dissolve ammonia in water
(D) To add energy from an external source

19. During air conditioning, whenever two or more streams of moist are mixed, they follow
(A) Adiabatic process
(B) Isothermal process
(C) Polytropic process
(D) Isobaric process

20. In a cooling tower, heat is dissipated mainly by 
(A) Radiation
(B) Conduction
(C) Convection
(D) Evaporation

Answers to these objective questions:

1-C, 2-B, 3-A, 4-C, 5-B, 6-D, 7-B, 8-B, 9-B, 10-D, 11-B, 12-D, 13-A, 14-A, 15-A, 16-B, 17-C, 18-A, 19-A, 20-D