Engineering Thermodynamics(Mechanical Engineering ) Questions and Answers

Question 1. Otto cycle efficiency is higher than Diesel cycle efficiency for the same compression ratio and heat input because in Otto cycle
  1.    Heat rejection is lower
  2.    Expansion and compression are isentropic
  3.    Combustion is at constant volume
  4.    Maximum temperature is higher
Explanation:-
Answer: Option A. -> Heat rejection is lower
Question 2. The molecular mass expressed in gram (i.e. 1 g - mole) of all gases, at N. T. P., occupies a volume of
  1.    0.224 liters
  2.    2.24 liters
  3.    22.4 liters
  4.    224 liters
Explanation:-
Answer: Option C. -> 22.4 liters
Question 3. Which of the following processes is irreversible process?
  1.    Isothermal
  2.    Adiabatic
  3.    Throttling
  4.    All of the above
Explanation:-
Answer: Option C. -> Throttling
Question 4. A diathermic wall is one which
  1.    Prevents thermal interaction
  2.    Permits thermal interaction
  3.    Encourages thermal interaction
  4.    Discourages thermal interaction
Explanation:-
Answer: Option B. -> Permits thermal interaction
Question 5. The amount of heat required to raise the temperature of the unit mass of gas through one degree at constant volume, is called
  1.    Kilo Joule
  2.    Specific heat at constant volume
  3.    Specific heat at constant pressure
  4.    None of these
Explanation:-
Answer: Option B. -> Specific heat at constant volume
Question 6. Addition of heat at constant pressure to a gas results in
  1.    Raising its temperature
  2.    Raising its pressure
  3.    Raising its volume
  4.    Raising its temperature and doing external work
Explanation:-
Answer: Option D. -> Raising its temperature and doing external work
Addition of heat at constant pressure to a gas results in Raising its temperature and doing external work
When you heat a gas, both its vapor pressure and the volume it occupies increase. The individual gas particles become more energetic and the temperature of the gas increases.
Question 7. Molecular volume of any perfect gas at 600 × 103 N/m2 and 27°C will be
  1.    4.17 m3/kg mol
  2.    400 m3/kg mol
  3.    0.15 m3/kg mol
  4.    41.7 m3/kg mol
Explanation:-
Answer: Option A. -> 4.17 m3/kg mol
Question 8. An actual engine is to be designed having same efficiency as the Carnot cycle. Such a proposition is
  1.    Feasible
  2.    Impossible
  3.    Possible
  4.    Possible, but with lot of sophistications
Explanation:-
Answer: Option D. -> Possible, but with lot of sophistications
Question 9. The absolute zero pressure can be attained at a temperature of
  1.    0°C
  2.    -273°C
  3.    273 K
  4.    None of these
Explanation:-
Answer: Option D. -> None of these
Correct Option is (B)
The lower the temperature, the lower the pressure inside of the sphere. If the exact values were plotted out, a linear relationship would be apparent. Extrapolating this line to the point where there would be no pressure yields absolute zero, which is about -273.15 degrees Celsius.
Question 10. Which of the following items is not a path function?
  1.    Heat
  2.    Work
  3.    Kinetic energy
  4.    Thermal conductivity
Explanation:-
Answer: Option D. -> Thermal conductivity
Heat and work are path functions because they depend on how a sysem changes from initial to final state, hence they are state functions. Thermal conductivity is mainly a function of the motion of the free electrons therefore property of a material, not a path function.
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