Engineering Thermodynamics — Part 1 MCQs with Explanations

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.

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.

According to the Carnot theorem, no engine operating between two constant temperature reservoirs can be more efficient than a Carnot engine operating between the same reservoirs. This means that achieving the same efficiency as the Carnot cycle with an actual engine is impossible, as it would violate the second law of thermodynamics. Therefore, the correct completion is: "An actual engine is to be designed having same efficiency as the Carnot cycle. Such a proposition is Impossible ."

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.

A homogeneous thermodynamic system is defined as the one whose chemical composition and physical properties are the same in all parts of the system, or change continuously from one point to another. An example of a heterogeneous system is water with ice floating in it. This system has two homogeneous bodies, water and ice. The chemical composition of the two phases is the same, but their physical properties differ drastically

The entropy (S) is a thermodynamic property that quantifies the degree of disorder or randomness in a system. It can be expressed as a function of various thermodynamic parameters. Option D, All of these , is the correct choice because entropy can indeed be expressed as a function of pressure and temperature, temperature and volume, as well as heat and work. Entropy as a function of pressure and temperature (S = f(P, T)) is applicable in various processes such as isothermal processes, isobaric processes, and adiabatic processes where pressure and temperature changes occur simultaneously. Entropy as a function of temperature and volume (S = f(T, V)) is relevant in processes like isentropic processes, where temperature and volume variations are significant. Entropy as a function of heat and work (S = f(Q, W)) is applicable in thermodynamic cycles such as the Carnot cycle, where the heat transfer (Q) and work done (W) are crucial parameters. Therefore, Option D correctly encompasses all these possibilities, making it the most suitable choice.

A molecule consisting of one atom is known as Mono-atomic In the gaseous phase at sufficiently high temperatures, all the chemical elements are monatomic gases.

One molecule of oxygen consists of two atoms of oxygen. Normally two oxygen atoms (denoted O); three bonded atoms of oxygen are called ozone (O)

The boiling point of a liquid is the temperature at which its vapor pressure is equal to the atmospheric pressure. When steam is passed through water, it heats the water, and if the pressure of the steam is greater than the atmospheric pressure, it can make the water boil even at a temperature below 100°C (the boiling point of water at atmospheric pressure). This phenomenon is utilized in various industrial processes, such as in steam generators and pressure cookers. When steam is supplied at a pressure higher than atmospheric pressure, the water in the beaker can be made to boil even at a temperature higher than 100°C. Among the options provided, the correct answer is Option B: At a pressure greater than atmospheric pressure . This is because boiling at a pressure higher than atmospheric pressure allows the water to reach its boiling point at a temperature higher than 100°C. Therefore, the correct answer is Option B: At a pressure greater than atmospheric pressure .

H = U + PV Where, H = Enthalpy, U = Internal energy, PV = Product of pressure & volume.

The Stirling cycle is a type of thermodynamic cycle that operates between two temperature limits, similar to the Carnot cycle. In theory, the efficiency of the Stirling cycle is equal to that of the Carnot cycle, as both are reversible cycles and achieve the maximum possible efficiency for a given temperature difference. This efficiency is determined by the Carnot efficiency, which depends solely on the temperature difference between the heat source and the heat sink.

The amount of heat required to raise the temperature of 1000 g (or 1 kg) of water through one degree Celsius is called a kilojoule. This is because the specific heat capacity of water is approximately 4.186 kJ/kg°C , meaning that 1 kg of water requires about 4.186 kJ to increase its temperature by 1°C. The smaller masses such as 1 g, 10 g, or 100 g would require proportionally less heat energy.

Apparently, the Brayton cycle and the Joule cycle are almost the same. The reversed Joule cycle is actually known as Bell-coleman cycle. Its purpose is to move heat, rather than produce work.

In the Diesel cycle, the efficiency approaches the efficiency of the Otto cycle when the cut-off is zero . The Diesel cycle consists of constant pressure heat addition followed by constant volume heat rejection. When the cut-off ratio is zero, the heat addition process in the Diesel cycle becomes constant volume (isochoric) instead of constant pressure. This is analogous to the heat addition process in the Otto cycle, where heat is added at constant volume. As a result, when the cut-off ratio is zero in the Diesel cycle, its thermal efficiency approaches that of the Otto cycle, which is higher due to the constant volume heat addition process. Therefore, the correct option is Option D: Cut-off is zero .

In a Brayton cycle without regeneration, the ideal efficiency increases with an increase in pressure ratio. The efficiency of a Brayton cycle without regeneration is given by: η = 1 - (1/r k-1 ) where η is the cycle efficiency, r is the pressure ratio (p max /p min ), and k is the specific heat ratio. As the pressure ratio increases, the denominator term (1/r k-1 ) decreases, resulting in a higher efficiency. Therefore, the correct option is Increase.

4.17 m3/kg mol is the correct answer to “Molecular volume of any perfect gas at 600 × 10 3 N/m 2 and 27°C will be”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

Diesel cycle is more efficient than Otto cycle is the correct answer to “For the same maximum pressure and temperature,”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

Coal gas is the correct answer to “Which of the following gas has the highest calorific value”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

None of the above is the correct answer to “Carbonization of coal consists of”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

1.4 is the correct answer to “The value of cp/cv for air is”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

Zero is the correct answer to “When cut-off ratio is ________; the efficiency of Diesel cycle approaches to Otto cycle efficiency”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

Thermodynamic cycle is the correct answer to “A series of operations, which takes place in a certain order and restore the initial conditions at the end, is known as”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

Molecule is the correct answer to “The smallest quantity of a substance, which can exist by itself in a chemically recognizable form is known as”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

4.187 is the correct answer to “The specific heat of water is”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

Constant pressure is the correct answer to “Change in enthalpy of a system is the heat supplied at”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

1 is the correct answer to “The general law of expansion or compression is pvn = C, The process is said to be hyperbolic, if n is equal to”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

Isothermal compression is the correct answer to “During which of the following process does heat rejection takes place in Carnot cycle”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

Kilogram is the correct answer to “The unit of mass in S.I. units is”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

Pascal is the correct answer to “The unit of pressure in S.I. units is”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

Meter is the correct answer to “The unit of length in S.I. units is”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

Joule is the correct answer to “The unit of energy in S.I. units is”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

Second is the correct answer to “The unit of time in S.I. units is”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

Kelvin is the correct answer to “The unit of temperature in S.I. units is”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

83.14 J/kmol°K is the correct answer to “The value of the product of molecular weight and the gas characteristic constant for all the gases in S.I. units is”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

26.03 bar is the correct answer to “The reading of the pressure gauge fitted on a vessel is 25 bar. The atmospheric pressure is 1.03 bar and the value of 'g' is 9.81 m/s 2 . The absolute pressure in the vessel is”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

Enthalpy is the correct answer to “Total heat of a substance is also known as”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

Constant volume cycle is the correct answer to “Otto cycle is also known as”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

0 is the correct answer to “The entropy of water at 0°C is assumed to be”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

Kinetic energy of the molecules is zero is the correct answer to “According to kinetic theory of gases, the absolute zero temperature is attained when”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.

First law of thermodynamics is the correct answer to “Energy can neither be created nor destroyed but can be converted from one form to other is inferred from”. This question is standard in competitive examination syllabi for Engineering Thermodynamics.