Thermodynamics MCQs 2026

Reheat in Rankine cycle primarily reduces

1. A boiler fuel need to zero ✓
2. B moisture content at turbine exit and blade erosion ✓
3. C pump work to zero always ✓
4. D condenser size to zero always ✓

Regeneration in Rankine cycle uses

1. A intercooling in Brayton compressor only as Rankine primary incorrectly ✓
2. B aftercooler in diesel only ✓
3. C feedwater heaters to preheat water using extracted steam ✓
4. D radiation shield only ✓

Quality (dryness fraction) x in wet steam region is

1. A mass of vapor divided by total mass of mixture ✓
2. B volume of liquid only ✓
3. C pressure divided by temperature ✓
4. D enthalpy of liquid only ✓

On T-s diagram, area under reversible process curve represents

1. A work always for any process without distinction incorrectly ✓
2. B heat transfer for that process ✓
3. C entropy generation equal to area always incorrectly ✓
4. D mass flow only ✓

On p-v diagram, area under process curve represents

1. A heat transfer always equal to area on pv incorrectly always ✓
2. B entropy change directly as area incorrectly ✓
3. C internal energy always ✓
4. D boundary work for quasi-static process ✓

Critical point on steam property chart is where

1. A liquid and vapor phases become indistinguishable ✓
2. B boiling always occurs at 100°C regardless of pressure incorrectly ✓
3. C entropy is zero always ✓
4. D quality equals zero only always at critical incorrectly alone ✓

Dry saturated steam has quality

1. A 1 ✓
2. B 0 ✓
3. C 0.5 always ✓
4. D undefined always incorrectly ✓

Subcooled liquid has temperature

1. A above saturation always ✓
2. B equal to critical always ✓
3. C below saturation temperature at given pressure ✓
4. D zero always ✓

Superheated steam has temperature

1. A below saturation ✓
2. B always at triple point ✓
3. C above saturation temperature at given pressure ✓
4. D equal to wet bulb always incorrectly ✓

Availability (exergy) of system interacting with environment at T0 is related to

1. A maximum useful work obtainable to dead state ✓
2. B total internal energy always equal to availability incorrectly ✓
3. C only kinetic energy ✓
4. D only gravitational PE always alone ✓

Irreversibility I in process equals

1. A T0 times entropy generation ✓
2. B work output always ✓
3. C heat input only without T0 ✓
4. D enthalpy change only ✓

Isothermal expansion of ideal gas in cylinder does

1. A no work ✓
2. B decrease U for ideal gas incorrectly in isothermal ✓
3. C positive work equal to heat added at constant T ✓
4. D zero heat transfer always ✓

Polytropic process p v^n = C with n=0 gives

1. A constant volume ✓
2. B constant pressure process ✓
3. C isothermal always ✓
4. D isentropic always ✓

Polytropic index n=1 corresponds to

1. A isochoric ✓
2. B isothermal process for ideal gas ✓
3. C isentropic ✓
4. D isobaric ✓

Polytropic index n=γ corresponds to

1. A isentropic process for ideal gas ✓
2. B isothermal ✓
3. C isobaric ✓
4. D isochoric ✓

Helmholtz function A is

1. A H − T S incorrectly as Helmholtz ✓
2. B pV only ✓
3. C T S only ✓
4. D U − T S ✓

Gibbs function G is

1. A U + pV only alone defines G incorrectly ✓
2. B T S − H ✓
3. C H − T S ✓
4. D pV − U ✓

Maxwell relations connect

1. A only mechanical stress and strain ✓
2. B partial derivatives of thermodynamic potentials ✓
3. C only Fourier law ✓
4. D only Navier-Stokes ✓

Joule-Thomson coefficient μ_JT is

1. A (∂p/∂T)_v ✓
2. B (∂T/∂p)_h ✓
3. C (∂h/∂p)_T only alone without definition incorrectly ✓
4. D (∂s/∂v)_T only alone ✓

Throttling of ideal gas causes

1. A no temperature change ✓
2. B always cooling regardless of gas incorrectly ✓
3. C always heating ✓
4. D phase change always ✓

Clausius inequality states for real cycles

1. A equal to zero always for irreversible too incorrectly ✓
2. B greater than zero always ✓
3. C independent of temperature ✓
4. D ∮ δQ/T ≤ 0 ✓

Entropy generation is always

1. A negative in irreversible processes incorrectly ✓
2. B zero for all irreversible processes incorrectly ✓
3. C non-negative for real processes ✓
4. D undefined for heat transfer ✓

Steady flow energy equation with negligible PE and KE changes reduces to

1. A Q − W_s = Δh for one stream ✓
2. B ΔU only always in SFEE incorrectly alone ✓
3. C ΔS only ✓
4. D p Δv only always alone sufficient ✓

Nozzle converts

1. A KE into heat only always in nozzle incorrectly ✓
2. B pressure rise without velocity change always ✓
3. C enthalpy decrease into kinetic energy increase ✓
4. D mass into energy ✓

Diffuser converts

1. A pressure into vacuum always ✓
2. B heat into work only in closed piston always incorrectly as diffuser primary ✓
3. C entropy decrease without irreversibility always in real diffuser incorrectly stated as always ✓
4. D kinetic energy into pressure rise ✓

Dew point temperature is temperature at which

1. A condensation begins for given moisture content at constant pressure ✓
2. B boiling occurs always at 100°C incorrectly regardless of pressure ✓
3. C entropy is maximum always ✓
4. D dry bulb equals wet bulb always for any air incorrectly ✓

Relative humidity is ratio of

1. A absolute humidity to density of dry air only without saturation reference incorrectly alone always as RH ✓
2. B wet bulb to dry bulb always as RH incorrectly ✓
3. C mass of liquid to mass of vapor in tank incorrectly as RH ✓
4. D partial pressure of vapor to saturation pressure at same temperature ✓

Throttling valve process is approximated as

1. A isentropic always for irreversible throttle incorrectly always ✓
2. B isochoric always ✓
3. C isothermal always for real gas always incorrectly ✓
4. D isenthalpic with negligible heat and work transfer ✓

Mixture of ideal gases total pressure is

1. A product of partial pressures ✓
2. B average only without summing incorrectly ✓
3. C zero if mixed ✓
4. D sum of partial pressures (Dalton) ✓

Partial pressure of component i is

1. A m_i P only mass fraction without conversion incorrectly always alone ✓
2. B P/n_i only incorrectly ✓
3. C y_i P where y_i is mole fraction ✓
4. D always equal for all components incorrectly ✓

Air-standard diesel cycle cut-off ratio affects

1. A only compression ratio of Otto only incorrectly alone always ✓
2. B only condenser pressure ✓
3. C heat addition at constant pressure and cycle efficiency ✓
4. D only pump work in Rankine incorrectly alone ✓

Mean effective pressure (MEP) in IC engines is

1. A peak pressure always equal to MEP incorrectly ✓
2. B work per cycle divided by displaced volume ✓
3. C fuel energy only without volume incorrectly ✓
4. D exhaust pressure only ✓

Knocking in SI engine is caused by

1. A too much steam injection incorrectly ✓
2. B auto-ignition of end-gas ahead of flame front ✓
3. C low compression always beneficial incorrectly ✓
4. D rankine reheat only incorrectly ✓

Octane number measures

1. A cetane for diesel incorrectly labeled as octane primary ✓
2. B viscosity only ✓
3. C calorific value only alone always as octane ✓
4. D knock resistance of fuel ✓

Cetane number measures

1. A knock resistance of gasoline incorrectly as cetane ✓
2. B ignition quality of diesel fuel ✓
3. C steam quality x incorrectly ✓
4. D hardness of coal incorrectly ✓

Turbocharger on engine uses

1. A exhaust energy to drive compressor for intake boost ✓
2. B crankshaft only without exhaust incorrectly alone always ✓
3. C electric battery only primary in standard turbo definition incorrectly alone ✓
4. D condenser cooling only ✓

Supercharger differs from turbocharger by being

1. A driven only by condenser pump incorrectly ✓
2. B only on steam turbine incorrectly ✓
3. C mechanically driven from crankshaft rather than exhaust turbine ✓
4. D only passive air filter incorrectly ✓

Internal energy of ideal gas depends on

1. A pressure and volume independently always additionally incorrectly for ideal gas U ✓
2. B temperature only ✓
3. C only volume ✓
4. D only pressure ✓

Enthalpy of ideal gas depends on

1. A only pressure independently always for h incorrectly for ideal gas ✓
2. B only specific volume independently always for h incorrectly ✓
3. C temperature only ✓
4. D only quality x of steam always incorrectly for ideal gas air ✓

Heat transfer at constant volume to ideal gas increases

1. A internal energy by Q since W=0 ✓
2. B enthalpy only without U change incorrectly always ✓
3. C nothing because W=0 incorrectly ✓
4. D only pressure without T change incorrectly always ✓

Heat transfer at constant pressure to ideal gas equals

1. A change in internal energy only always at cp incorrectly always alone ✓
2. B zero always ✓
3. C change in enthalpy ΔH ✓
4. D only entropy decrease incorrectly ✓

Free expansion into vacuum (Joule expansion) of ideal gas has

1. A no temperature change and no work ✓
2. B large cooling always for ideal gas incorrectly always ✓
3. C large heating always ✓
4. D isentropic behavior always incorrectly ✓

Gouy-Stodola theorem links

1. A stress and strain only ✓
2. B lost work to irreversibility and T0 ✓
3. C Fourier law only ✓
4. D Darcy law only ✓

Saturated liquid and vapor lines meet at

1. A critical point on property diagrams ✓
2. B triple point only always incorrectly as meeting of sat lines termination on dome ✓
3. C origin always ✓
4. D absolute zero always ✓

Isentropic expansion of steam in turbine ideally follows

1. A constant temperature line always incorrectly as isentropic always ✓
2. B constant h line on ph chart as isentropic primary incorrectly alone always ✓
3. C constant entropy line on T-s diagram ✓
4. D constant quality line in wet region always entire expansion incorrectly always ✓

Boiler in Rankine cycle operates ideally near

1. A constant volume heat addition as Otto primary incorrectly alone for boiler ✓
2. B constant pressure heat addition ✓
3. C isothermal heat rejection ✓
4. D adiabatic compression in boiler incorrectly ✓

Volumetric efficiency of engine is

1. A thermal efficiency incorrectly labeled ✓
2. B actual mass inducted divided by mass at STP filling displacement ✓
3. C mechanical efficiency incorrectly labeled ✓
4. D isentropic efficiency of turbine incorrectly labeled ✓

Zeroth law of thermodynamics establishes

1. A conservation of energy ✓
2. B entropy always increases in isolated system ✓
3. C impossibility of perpetual motion only ✓
4. D transitivity of thermal equilibrium and temperature concept ✓

First law of thermodynamics for closed system is

1. A ΔU = Q + W always regardless of convention ✓
2. B Q = 0 always ✓
3. C ΔU = Q − W with work done by system positive in common convention ✓
4. D W = m g h only ✓

Second law of thermodynamics implies

1. A energy is created ✓
2. B efficiency of heat engine can be 100% always ✓
3. C entropy always decreases in isolated system ✓
4. D natural processes tend toward increased total entropy of universe ✓

Third law of thermodynamics states entropy approaches

1. A infinity at 0 K always for all substances ✓
2. B constant at all temperatures ✓
3. C zero as absolute temperature approaches zero for perfect crystals ✓
4. D negative values only ✓

Enthalpy H is defined as

1. A U − pV ✓
2. B p/V ✓
3. C U/pV ✓
4. D U + pV ✓

Specific heat at constant pressure cp is

1. A (∂u/∂T)_v only always interchangeable without distinction ✓
2. B (∂p/∂T)_v ✓
3. C (∂v/∂T)_p only alone defines cp ✓
4. D (∂h/∂T)_p ✓

Entropy change for ideal gas between two states

1. A depends on states not path when computed via reversible path ✓
2. B depends only on path always for all properties incorrectly ✓
3. C depends only on pressure always without temperature ✓
4. D depends only on volume always without mass ✓

Isentropic process for ideal gas satisfies

1. A p v = constant always for all processes ✓
2. B T/p = constant only always ✓
3. C p v^γ = constant ✓
4. D entropy increases always ✓

Carnot cycle efficiency depends on

1. A temperatures of hot and cold reservoirs only ✓
2. B working substance only ✓
3. C pressure ratio only without temperatures ✓
4. D piston speed only ✓

Carnot theorem states no engine between two reservoirs exceeds efficiency of

1. A any irreversible engine always lower than Carnot incorrectly as theorem wording ✓
2. B 100% if operated quickly ✓
3. C engine independent of temperature difference ✓
4. D reversible Carnot engine between same reservoirs ✓

Otto cycle is idealized model for

1. A steam turbine only ✓
2. B gas turbine Brayton only ✓
3. C vapor compression refrigerator only as power cycle ✓
4. D spark-ignition gasoline engine ✓

Otto cycle efficiency increases with

1. A compression ratio ✓
2. B decreasing compression ratio ✓
3. C increasing exhaust back pressure only beneficial always ✓
4. D water injection alone as sole lever incorrectly ✓

Diesel cycle differs from Otto mainly by

1. A constant pressure heat addition ✓
2. B constant volume heat rejection only as sole difference incorrectly ✓
3. C no compression stroke ✓
4. D isothermal expansion only entire cycle ✓

Diesel cycle efficiency compared to Otto at same compression ratio is generally

1. A always lower without exception ✓
2. B always equal regardless of cut-off ✓
3. C zero ✓
4. D higher due to different heat addition path with cut-off ✓

Rankine cycle is used for

1. A steam power plants ✓
2. B gasoline engines only ✓
3. C vapor compression refrigeration only as primary power ✓
4. D hydraulic turbines only ✓

Rankine cycle efficiency improves by

1. A increasing average temperature of heat addition and lowering condenser pressure ✓
2. B lowering boiler temperature always beneficial incorrectly ✓
3. C increasing condenser pressure always beneficial incorrectly ✓
4. D removing pump always ✓

Brayton cycle is model for

1. A gas turbine engine ✓
2. B Rankine steam plant only ✓
3. C Otto SI engine only ✓
4. D vapor compression refrigerator only as power primary incorrectly ✓

Brayton cycle efficiency depends on

1. A only fuel type without cycle parameters incorrectly alone ✓
2. B only turbine blade count ✓
3. C pressure ratio and γ ✓
4. D only condenser temperature as Rankine incorrectly alone ✓

Intercooling in multi-stage compression reduces

1. A turbine work always increases beneficially incorrectly as primary intercooling effect on turbine ✓
2. B compressor work and final temperature ✓
3. C mass flow to zero ✓
4. D cycle efficiency always decreases without exception incorrectly always ✓

Reheat in Brayton cycle can

1. A increase net work but may reduce efficiency if not optimized ✓
2. B always reduce work ✓
3. C eliminate combustion ✓
4. D make cycle identical to Rankine always ✓

Combined cycle plant pairs

1. A only two Rankine cycles in parallel without GT incorrectly alone ✓
2. B Brayton topping with Rankine bottoming using exhaust heat ✓
3. C only refrigeration cycle ✓
4. D hydraulic and wind only ✓

COP of heat pump is

1. A work divided by heat always inverted incorrectly ✓
2. B always less than 1 for heat pump incorrectly always ✓
3. C desired heat effect divided by work input ✓
4. D independent of temperatures ✓

COP of refrigerator is

1. A heating effect divided by work for refrigerator incorrectly ✓
2. B always greater than Carnot incorrectly always ✓
3. C Q_H/W for refrigerator incorrectly ✓
4. D cooling effect divided by work input ✓

Carnot COP for refrigerator between T_L and T_H is

1. A T_H/(T_H − T_L) which is heat pump COP incorrectly labeled as refrigerator ✓
2. B T_L/(T_H − T_L) ✓
3. C 1 − T_L/T_H ✓
4. D (T_H − T_L)/T_L inverted incorrectly ✓

Triple point of water occurs at approximately

1. A 100°C and 1 atm always incorrectly as triple point ✓
2. B 0 K ✓
3. C 374°C always ✓
4. D 0.01°C and 611 Pa ✓

Specific volume of saturated mixture equals

1. A v_g only always ✓
2. B v_f + x(v_g − v_f) ✓
3. C v_f only always regardless of x incorrectly ✓
4. D x v_f only incorrectly ✓

Enthalpy of wet steam mixture is

1. A h_g only always ✓
2. B h_f only always regardless of quality incorrectly always ✓
3. C h_f + x h_fg ✓
4. D x h_g only incorrectly alone always ✓

Entropy change of ideal gas between two states can be found using

1. A only density measurement ✓
2. B cp ln(T2/T1) − R ln(p2/p1) for ideal gas ✓
3. C only color of gas ✓
4. D only piston material ✓

Van der Waals equation accounts for

1. A only ideal gas behavior always perfectly ✓
2. B only radiation heat transfer ✓
3. C only turbulence ✓
4. D molecular volume and intermolecular attraction ✓

Compressibility factor Z equals

1. A RT/(pv) inverted always as definition incorrectly ✓
2. B γ always ✓
3. C cp/cv always ✓
4. D pV/(mRT) or pv/(RT) ✓

Law of corresponding states suggests

1. A all gases identical at any T,p without reduced coordinates incorrectly ✓
2. B real gases at same reduced T and p have similar Z ✓
3. C only liquids follow ✓
4. D only solids follow ✓

Mollier chart for steam plots

1. A stress versus strain ✓
2. B velocity versus time only ✓
3. C current versus voltage only ✓
4. D enthalpy versus entropy with pressure overlays ✓

Isentropic efficiency of turbine is ratio of

1. A isentropic to actual inverted incorrectly as definition ✓
2. B actual work to isentropic work for same inlet state and exit pressure ✓
3. C heat transfer to work incorrectly ✓
4. D inlet KE to exit KE only ✓

Isentropic efficiency of compressor is ratio of

1. A actual to isentropic inverted for compressor definition incorrectly ✓
2. B heat to entropy always ✓
3. C isentropic work to actual work for same states ✓
4. D mass flow ratios only ✓

Heat engine thermal efficiency η is

1. A Q_L/Q_H incorrectly ✓
2. B Q_H/Q_L inverted beneficial incorrectly ✓
3. C work input divided by heat ✓
4. D net work output divided by heat input from hot reservoir ✓

Kelvin-Planck statement of second law denies

1. A heat flow from cold to hot without work incorrectly as Kelvin-Planck primary alone ✓
2. B device producing work from single heat reservoir alone ✓
3. C conservation of mass ✓
4. D existence of temperature ✓

Clausius statement of second law denies

1. A work from single reservoir incorrectly as Clausius primary ✓
2. B increase of entropy in universe incorrectly stated as denied ✓
3. C spontaneous heat transfer from cold to hot body without external work ✓
4. D phase change existence ✓

Perpetual motion machine of first kind violates

1. A second law only ✓
2. B first law of thermodynamics ✓
3. C third law only ✓
4. D zeroth law only ✓

Perpetual motion machine of second kind violates

1. A second law of thermodynamics ✓
2. B first law only ✓
3. C Newton laws only ✓
4. D continuity equation only ✓

Psychrometric chart displays

1. A properties of moist air including humidity ratio and enthalpy ✓
2. B only steam inside boiler without air ✓
3. C only metal stress ✓
4. D only beam shear flow ✓

Entropy of isolated system during real spontaneous process

1. A always decreases ✓
2. B always zero change ✓
3. C increases or remains constant never decreases ✓
4. D decreases if heat added incorrectly always ✓

Air-standard Otto cycle consists of

1. A constant pressure heat addition only as Otto incorrectly ✓
2. B isothermal compression only entire cycle ✓
3. C rankine pump stage included ✓
4. D isentropic compression, constant volume heat addition, isentropic expansion, constant volume heat rejection ✓

Steam calorimetry throttling calorimeter measures

1. A bolt preload only ✓
2. B quality of wet steam by isenthalpic expansion to superheat region ✓
3. C shaft diameter only ✓
4. D Reynolds number only ✓