Question 1

Gas law check (Gay-Lussac/Amontons law): judge the statement  Statement: “For a perfect gas at constant volume, p/T = constant.”  Choose whether the statement is correct or incorrect.

Accepted Answer

Concept/Approach From the ideal gas equation pV = nRT, with V and n constant, p ∝ T ⇒ p/T = constant. Final Answer Agree — at constant volume, pressure is directly proportional to temperature.

Question 2

Irreversibility versus heat loss: judge the statement  Statement: “There is a loss of heat in an irreversible process.”  Choose whether the statement is correct or incorrect.

Accepted Answer

Concept/Approach Irreversibility is about entropy production due to finite gradients, friction, mixing, shocks, etc. Heat loss is neither necessary nor sufficient for irreversibility. Illustration Adiabatic throttling (Joule–Thomson) is irreversible with no heat transfer (Q = 0).Conversely, a reversible isothermal process transfers heat but can be reversible. Final Answer Disagree — irreversibility is about entropy generation, not necessarily about heat loss.

Question 3

Fuel sources: decide correctness of the statement  Statement: “All the commercial liquid fuels are derived from natural petroleum (crude oil).”  Choose whether the statement is correct or incorrect (as per conventional thermal-engineering classifica…

Accepted Answer

Concept/Approach Conventional commercial liquid fuels (gasoline/petrol, kerosene, diesel, furnace oil, LDO/HFO) are petroleum distillates or blends from crude-oil refining. Though alternative liquids like ethanol exist, classic textbooks typically classify commercial liquid fuels as petroleum derived. Final Answer Agree — in the usual engineering classification, commercial liquid fuels are derived from crude oil.

Question 4

Diesel versus Otto cycle: effect of cut-off ratio on efficiency  Fill the blank: “When the cut-off ratio is _____, the efficiency of the Diesel cycle approaches the Otto cycle efficiency.”  Choose the correct value.

Accepted Answer

Concept/Approach Cut-off ratio rc = V3/V2 during constant-pressure heat addition in the Diesel cycle. As rc → 1, the heat addition tends to constant volume; Diesel tends to the Otto cycle. Diesel efficiency (air-standard, schematic) ηD = 1 − (1/rkγ−1) · [(rcγ − 1)/(γ(rc − 1))]Taking rc → 1 gives the Otto efficiency: ηO = 1 − 1/rkγ−1. Final Answer 1 (unity)

Question 5

Simple Brayton (gas turbine) cycle: typical performance How are the thermal efficiency and the work ratio of a simple (un-regenerated, un-intercooled, un-reheated) gas turbine cycle generally characterized? Choose the best descri…

Accepted Answer

Concept/Approach In a simple Brayton cycle, a large fraction of turbine work is consumed by the compressor, yielding a low work ratio (Wnet/WT). Without regeneration/reheat/intercooling, the thermal efficiency is also modest. Typical trend Increasing pressure ratio raises efficiency up to an optimum, but simple cycles still remain “low” compared with improved cycles. Final Answer Low

Question 6

Open systems and mass transfer: name the process type  Definition prompt: “Processes occurring in an open system that permit transfer of mass to and from the system are known as …”  Choose the correct term.

Accepted Answer

Concept/Approach An open system exchanges mass with surroundings; processes with mass flow across the boundary are termed flow processes. Non-flow processes apply to closed systems (no mass transfer). Final Answer Flow processes

Question 7

Ratio of specific heats γ = cp/cv: decide its magnitude For a gas, compare the ratio of specific heats γ = c_p/c_v with unity. Choose the correct relation.

Accepted Answer

Concept/Approach For ideal gases: cp − cv = R > 0 ⇒ cp > cv. Therefore γ = cp/cv > 1. Final Answer Greater than one

Question 8

Universal gas constant vs. specific gas constant: verify the relationship  Statement: The universal gas constant of a gas equals the product of the gas’s molecular mass and its (specific) gas constant per unit mass. Choose whether the statement is c…

Accepted Answer

Concept The two common gas constants are related by molecular mass (M): Universal gas constant: R ≈ 8.314 kJ/(kmol·K) = 8,314 J/(mol·K) Specific gas constant (per unit mass): Rspecific = R / M Relationship R = M × Rspecific Common pitfalls Do not confuse molar mass units (kg/kmol or g/mol) with mass units; ensure consistency so that R and Rspecific align dimensionally. Final Answer True

Question 9

Isothermal process law: identify the governing gas law  For an isothermal (constant-temperature) process of an ideal gas, select the correct law that applies. Choose the correct option.

Accepted Answer

Concept For an isothermal process (T constant) of an ideal gas, the pressure–volume product remains constant: pV = constant. This is exactly Boyle's law. Why the others are incorrect Charles' law is V ∝ T at constant p; Gay-Lussac's is p ∝ T at constant V; Avogadro's relates equal volumes to equal moles at the same T and p. Final Answer Boyle's law

Question 10

Thermal efficiency comparison: Stirling cycle versus Carnot cycle  State how the efficiency of the (reversible, regenerator-based) Stirling cycle compares with a Carnot cycle operating between the same temperature limits. Choose the correct relation…

Accepted Answer

Concept A Stirling cycle with perfect regeneration is a reversible cycle. All reversible heat engines operating between the same two thermal reservoirs have the same efficiency—namely that of the Carnot cycle: η = 1 − Tc/Th. Conclusion Thus, the efficiency of an ideal Stirling cycle equals the Carnot efficiency for the same temperature limits. Final Answer Equal to Carnot cycle

Question 11

According to Kelvin-Planck's statement of second law of thermodynamics,

Accepted Answer

it is impossible to construct an engine working on a cyclic process, whose sole purpose is to convert heat energy into work

Question 12

The area under the temperature-entropy curve (T - s curve) of any thermodynamic process represents

Accepted Answer

either (a) or (b)

Question 13

For a perfect gas, according to Boyle's law (where p = Absolute pressure, v = Volume, and T = Absolute temperature)

Accepted Answer

p v = constant, if T is kept constant

Question 14

According to Gay-Lussac law, the absolute pressure of a given mass of a perfect gas varies __________ as its absolute temperature, when the volume remains constant.

Accepted Answer

directly

Question 15

The efficiency of Diesel cycle depends upon

Accepted Answer

cut-off ratio and compression ratio

Question 16

The general gas energy equation is (where Q1 - 2 = Heat supplied, dU = Change in internal energy, and W1 - 2 = Work done in heat units)

Accepted Answer

Q1 - 2 = dU + W1 - 2

Question 17

The dual combustion cycle consists of one constant pressure, two constant volume and two isentropic processes.

Accepted Answer

Agree

Question 18

When two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other. This statement is called

Accepted Answer

Zeroth law of thermodynamics

Question 19

Kelvin-Planck's law deals with

Accepted Answer

conversion of heat into work

Thermodynamics Questions