Mechanical Engineering Thermodynamics – Set 01

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Q1. When a gas is heated, change takes place in

(A) Temperature
(B) Pressure
(C) Volume
(D) All of these

Answer: (D) All of these


Q2. According to Dalton’s law, the total pressure of the mixture of gases is equal to

(A) Greater of the partial pressures of all
(B) Average of the partial pressures of all
(C) Sum of the partial pressures of all
(D) Sum of the partial pressures of all divided by average molecular weight

Answer: (C) Sum of the partial pressures of all


Q3. Superheated vapour behaves

(A) Exactly as gas
(B) As steam
(C) As ordinary vapour
(D) Approximately as a gas

Answer: (D) Approximately as a gas


Q4. The specific heat of water is

(A) 2.512
(B) 1.817
(C) 4.187
(D) None of these

Answer: (C) 4.187


Q5. Which of the following is the property of a system?

(A) Pressure and temperature
(B) Volume and density
(C) Enthalpy and entropy
(D) All of the above

Answer: (D) All of the above


Q6. In an isothermal process, the internal energy of gas molecules

(A) Increases
(B) Decreases
(C) Remain constant
(D) May increase/decrease depending on the properties of gas

Answer: (C) Remain constant


Q7. In a free expansion process

(A) Work done is zero
(B) Heat transfer is zero
(C) Both (A) and (B) above
(D) Work done is zero but heat increases

Answer: (C) Both (A) and (B) above


Q8. Isochoric process is one in which

(A) Free expansion takes place
(B) Very little mechanical work is done by the system
(C) No mechanical work is done by the system
(D) All parameters remain constant

Answer: (C) No mechanical work is done by the system


Q9. Carnot cycle efficiency is maximum when

(A) Initial temperature is 0°K
(B) Final temperature is 0°K
(C) Difference between initial and final temperature is 0°K
(D) Final temperature is 0°C

Answer: (B) Final temperature is 0°K


Q10. The gas constant (R) is equal to the __ of two specific heats.

(A) Product
(B) Sum
(C) Difference
(D) Ratio

Answer:(C) Difference


Q11. According to Gay Lussac’s law for a perfect gas, the absolute pressure of given mass varies directly as

(A) Temperature
(B) Absolute temperature, if volume is kept constant
(C) Volume, if temperature is kept constant
(D) None of these

Answer: (B) Absolute temperature, if volume is kept constant


Q12. Which of the following quantities is not the property of the system?

(A) Pressure
(B) Temperature
(C) Specific volume
(D) Heat

Answer: (D) Heat


Q13. The more effective way of increasing efficiency of Carnot engine is to

(A) Increase higher temperature
(B) Decrease higher temperature
(C) Increase lower temperature
(D) Decrease lower temperature

Answer: (D) Decrease lower temperature


Q14. The efficiency of Diesel cycle approaches to Otto cycle efficiency when

(A) Cut-off is decreased
(B) Cut-off is constant
(C) Cut-off is increased
(D) Cut-off is zero

Answer: (B) Cut-off is constant


Q15. Stirling and Ericsson cycles are

(A) Reversible cycles
(B) Irreversible cycles
(C) Semi-reversible cycles
(D) Adiabatic irreversible cycles

Answer:(A) Reversible cycles


Q16. One molecule of oxygen consists of __ atoms of oxygen.

(A) 2
(B) 4
(C) 8
(D) 16

Answer: (A) 2


Q17. Which of the following can be regarded as gas so that gas laws could be applicable, within the commonly encountered temperature limits?

(A) O₂, N₂, steam, CO₂
(B) O₂, N₂, water vapour
(C) SO₂, NH₃, CO₂, moisture
(D) O₂, N₂, H₂, air

Answer: (D) O₂, N₂, H₂, air


Q18. Absolute zero pressure will occur

(A) At sea level
(B) When molecular momentum of the system becomes zero
(C) Under vacuum conditions
(D) At a temperature of 273°K

Answer: (B) When molecular momentum of the system becomes zero


Q19. According to which law, all perfect gases change in volume by 1/273th of their original volume at 0°C for every 1°C change in temperature when pressure remains constant

(A) Joule’s law
(B) Boyle’s law
(C) Gay Lussac’s law
(D) Charles’ law

Answer: (D) Charles’ law


Q20. On weight basis, air contains following parts of oxygen

(A) 21
(B) 23
(C) 25
(D) 73

Answer: (B) 23


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