📘 Thermodynamic Properties & Basic Concepts
BOOK LINK-
MCQ 1
Which of the following is an intensive property?(MPPSC SI TRANSPORT BOOK )
A) Volume
B) Mass
C) Temperature
D) Entropy
Answer: C) Temperature
Explanation:
- Intensive properties do not depend on the system size (e.g., temperature, pressure, density).
- Extensive properties depend on system size (e.g., volume, mass, entropy).
MCQ 2
Which of the following is an extensive property?(MPPSC SI TRANSPORT BOOK )
A) Pressure
B) Internal Energy
C) Temperature
D) Density
Answer: B) Internal Energy
Explanation:
- Extensive properties add up with system size. Internal energy is proportional to mass/volume.
- Pressure, temperature, density → intensive properties.
MCQ
The ratio of two extensive properties always results in:(MPPSC SI TRANSPORT BOOK )
A) Intensive property
B) Extensive property
C) Zero
D) Infinite
Answer: A) Intensive property
Explanation:
For example, mass/volume = density. Internal energy/mass = specific energy → both are intensive.
MCQ 4
Which property determines if two systems are in thermal equilibrium?(MPPSC SI TRANSPORT BOOK )
A) Pressure
B) Volume
C) Temperature
D) Density
Answer: C) Temperature
Explanation:
According to the Zeroth Law of Thermodynamics, thermal equilibrium is based on temperature equality.
MCQ 5
Which of the following is a point function?(MPPSC SI TRANSPORT BOOK )
A) Work
B) Heat
C) Temperature
D) Path traversed
Answer: C) Temperature
Explanation:
- Point functions depend only on the state (P, T, V, U, H, etc.).
- Path functions (Q, W) depend on the process.
MCQ 6
Which one of the following is not a thermodynamic property?(MPPSC SI TRANSPORT BOOK )
A) Enthalpy
B) Kinetic Energy
C) Work
D) Entropy
Answer: C) Work
Explanation:
Work is an energy interaction (path function), not a property. Properties are measurable or calculable and describe the system state.
MCQ 7
In a quasi-static process, the system:(MPPSC SI TRANSPORT BOOK )
A) Moves very fast
B) Remains at equilibrium at every stage
C) Never attains equilibrium
D) Is irreversible
Answer: B) Remains at equilibrium at every stage
Explanation:
Quasi-static = infinitely slow process → system passes through continuous equilibrium states.
MCQ 8
Which one is a path function?(MPPSC SI TRANSPORT BOOK )
A) Temperature
B) Pressure
C) Heat
D) Volume
Answer: C) Heat
Explanation:
- Heat & work → path functions.
- Temperature, pressure, volume → point functions.
MCQ 9
A cycle that returns to its initial state has a net change in:(MPPSC SI TRANSPORT BOOK )
A) Internal energy = 0
B) Work done = 0
C) Heat rejected = 0
D) Enthalpy = 0
Answer: A) Internal energy = 0
Explanation:
Internal energy is a property (state function). Over a cycle (final = initial), change in U = 0.
MCQ 10
Specific heat at constant volume is given by:(MPPSC SI TRANSPORT BOOK )
A) Cv=(dUdT)vCv=(dTdU)v
B) Cv=(dHdT)pCv=(dTdH)p
C) Cv=TdSdTCv=TdTdS
D) Cv=QWCv=WQ
Answer: A) Cv=(dUdT)vCv=(dTdU)v
Explanation:
At constant volume, δQ = dU = mC_v dT.
MCQ 11
Which statement about Zeroth Law is correct?(MPPSC SI TRANSPORT BOOK )
A) Defines heat
B) Defines temperature
C) Defines entropy
D) Defines energy
Answer: B) Defines temperature
Explanation:
Zeroth Law forms the basis of temperature measurement and thermal equilibrium.
MCQ 12
The property not used as a thermodynamic coordinate is:(MPPSC SI TRANSPORT BOOK )
A) Pressure
B) Mass
C) Temperature
D) Entropy
Answer: B) Mass
Explanation:
- Mass is important but not used as a coordinate in thermodynamic diagrams (like P–V, T–S).
MCQ 13
Which is an example of a closed system?(MPPSC SI TRANSPORT BOOK )
A) Cylinder with a piston and no mass exchange
B) Jet engine
C) Nozzle
D) Turbine
Answer: A) Cylinder with piston
Explanation:
- Closed system → no mass crosses boundary (only energy).
- Jet engine, nozzle, turbine → open systems.
MCQ 14
Which one of the following describes an open system?(MPPSC SI TRANSPORT BOOK )
A) No exchange of mass or energy
B) Mass exchange only
C) Both mass and energy exchange
D) Energy exchange only
Answer: C) Both mass and energy exchange
Explanation:
Examples: compressor, turbine, boiler.
MCQ 15
The best example of isolated system is:(MPPSC SI TRANSPORT BOOK )
A) Thermos flask
B) Heat exchanger
C) Steam turbine
D) Refrigerator
Answer: A) Thermos flask
Explanation:
An isolated system ideally exchanges neither mass nor energy. Thermos approximates it.
MCQ 16
Property related to randomness of particles is:(MPPSC SI TRANSPORT BOOK )
A) Enthalpy
B) Entropy
C) Internal energy
D) Temperature
Answer: B) Entropy
Explanation:
Entropy measures molecular disorder/chaos.
MCQ 17
The thermodynamic property equal to heat supplied at constant pressure is:(MPPSC SI TRANSPORT BOOK )
A) Work
B) Enthalpy change
C) Entropy
D) Internal energy
Answer: B) Enthalpy change
Explanation:
At constant pressure: Qp=ΔHQp=ΔH.
MCQ 18
Equation of state relates:(MPPSC SI TRANSPORT BOOK )
A) Properties of path
B) Properties of process
C) Thermodynamic coordinates
D) Work and heat
Answer: C) Thermodynamic coordinates
Explanation:
Equation of state (like PV=nRTPV=nRT) relates P, V, T.
MCQ 19
A process in which entropy remains constant is:(MPPSC SI TRANSPORT BOOK )
A) Isothermal
B) Adiabatic
C) Isochoric
D) Isentropic
Answer: D) Isentropic
Explanation:
Isentropic = reversible adiabatic (ΔS = 0).
MCQ 20
In a thermodynamic cycle, the net work output equals:(MPPSC SI TRANSPORT BOOK )
A) ΔQ – ΔU
B) Net heat added
C) ΔU
D) ΔH
Answer: B) Net heat added
Explanation:
From 1st Law over cycle: ΔU = 0 ⇒ Net Q = Net W.
MCQ 21
The Zeroth Law of Thermodynamics deals with:(MPPSC SI TRANSPORT BOOK )
A) Conservation of energy
B) Entropy
C) Thermal equilibrium
D) Heat transfer
Answer: C) Thermal equilibrium
Explanation:
- Zeroth Law states: If system A is in thermal equilibrium with B, and B is with C, then A and C are also in equilibrium.
- Basis of temperature measurement.
MCQ 22
The most fundamental concept introduced by the Zeroth Law is:(MPPSC SI TRANSPORT BOOK )
A) Work
B) Internal energy
C) Temperature
D) Pressure
Answer: C) Temperature
Explanation:
Thermometers are possible because temperature is defined via the Zeroth Law.
MCQ 23
Two systems each in thermal equilibrium with a third one are:(MPPSC SI TRANSPORT BOOK )
A) Not in equilibrium with each other
B) In equilibrium with each other
C) Can’t be compared
D) Neither (a) nor (b)
Answer: B) In equilibrium with each other
Explanation:
That is precisely the statement of the Zeroth Law.
MCQ 24
Which device works on the principle of the Zeroth Law?(MPPSC SI TRANSPORT BOOK )
A) Turbine
B) Thermometer
C) Heat exchanger
D) Compressor
Answer: B) Thermometer
Explanation:
A thermometer comes into thermal equilibrium with a body → measures its temperature.
MCQ 25
The first law of thermodynamics is a statement of:(MPPSC SI TRANSPORT BOOK )
A) Creation of energy
B) Destruction of energy
C) Conservation of energy
D) Irreversibility
Answer: C) Conservation of energy
Explanation:
Energy cannot be created/destroyed, only transformed.
MCQ 26
For a cyclic process, first law reduces to:(MPPSC SI TRANSPORT BOOK )
A) ∮ δQ = ∮ δW
B) ∮ δQ = 0
C) ∮ δW = 0
D) ΔU = constant
Answer: A) ∮ δQ = ∮ δW
Explanation:
Over a cycle, ΔU = 0 ⇒ heat interaction = work interaction.
MCQ 27
The internal energy depends on:(MPPSC SI TRANSPORT BOOK )
A) Pressure and entropy
B) Temperature and mass
C) Heat and work interactions
D) Path followed
Answer: B) Temperature and mass
Explanation:
For ideal gases, U=f(T)U=f(T). It is a function of state, not path.
MCQ 28
Change in internal energy of a system depends on:(MPPSC SI TRANSPORT BOOK )
A) Initial and final condition only
B) Path followed
C) Work interaction only
D) Heat interaction only
Answer: A) Initial and final condition only
Explanation:
Internal energy is a property (point function). So ΔU depends only on states, not process.
MCQ 29
In a closed system undergoing adiabatic process with work done by the system:(MPPSC SI TRANSPORT BOOK )
A) Internal energy decreases
B) Internal energy increases
C) No change in internal energy
D) Cannot be predicted
Answer: A) Internal energy decreases
Explanation:
No heat transfer (adiabatic), so work output comes by decreasing internal energy.
MCQ 30
When a closed system undergoes an adiabatic process, which is true?(MPPSC SI TRANSPORT BOOK )
A) Heat transfer ≠ 0
B) Heat transfer = 0
C) Work transfer = 0
D) Temperature constant
Answer: B) Heat transfer = 0
Explanation:
By definition, adiabatic = no heat exchange.
MCQ 31
In the first law applied to a closed system:(MPPSC SI TRANSPORT BOOK )
A) δQ = dU – δW
B) δQ = dU + δW
C) dU = δQ + δW
D) dU = δQ – δW
Answer: D) dU = δQ – δW
Explanation:
Convention: Heat added (+), Work done by system (+). So:
dU=δQ−δWdU=δQ−δW
MCQ 32
Work done in a quasi-static process is given by:(MPPSC SI TRANSPORT BOOK )
A) W = ∫ p dv
B) W = ∫ T ds
C) W = ∫ p dT
D) W = ∫ v dp
Answer: A) W=∫p dVW=∫pdV
Explanation:
For reversible (quasi-static) processes → area under P–V curve.
MCQ 33
The unit of specific enthalpy is:(MPPSC SI TRANSPORT BOOK )
A) kJ
B) kJ/kg
C) J·mol⁻¹
D) kW
Answer: B) kJ/kg
Explanation:
Specific enthalpy = enthalpy per unit mass.
MCQ 34
A system receives 100 kJ of heat and does 60 kJ of work. Change in internal energy is:(MPPSC SI TRANSPORT BOOK )
A) 40 kJ increase
B) 60 kJ increase
C) 160 kJ increase
D) 40 kJ decrease
Answer: A) 40 kJ increase
Explanation:
First law: ΔU = Q – W = 100 – 60 = 40 kJ (increase).
MCQ 35
A system absorbs 200 kJ of heat while 50 kJ of work is done on it. The change in internal energy is:(MPPSC SI TRANSPORT BOOK )
A) 250 kJ
B) 150 kJ
C) 100 kJ
D) 300 kJ
Answer: A) 250 kJ
Explanation:
ΔU = Q – W(by system).
Work done on system = –W = –(–50) ⇒ W = –50.
So ΔU = 200 – (–50) = 250 kJ.
MCQ 36
At constant volume, the heat supplied to a system is equal to the change in:(MPPSC SI TRANSPORT BOOK )
A) Enthalpy
B) Internal energy
C) Entropy
D) Work
Answer: B) Internal energy
Explanation:
dQ = dU at constant volume (since δW = PdV = 0).
MCQ 37
At constant pressure, the heat supplied to a system is equal to change in:(MPPSC SI TRANSPORT BOOK )
A) Internal energy
B) Work
C) Enthalpy
D) Entropy
Answer: C) Enthalpy
Explanation:
At constant P: Qp=ΔHQp=ΔH.
MCQ 38
Which of the following can increase both internal energy and enthalpy of a system?(MPPSC SI TRANSPORT BOOK )
A) Addition of work only
B) Addition of heat only
C) Addition of heat and compression work
D) Heat loss
Answer: C) Addition of heat and compression work
Explanation:
Both increase molecular energy content.
MCQ 39
A system undergoes a process in which ΔU = 150 kJ and work done by the system = 100 kJ. Heat transfer is:(MPPSC SI TRANSPORT BOOK )
A) 50 kJ
B) 100 kJ
C) 250 kJ
D) 150 kJ
Answer: C) 250 kJ
Explanation:
First law: ΔU = Q – W → Q = ΔU + W = 150 + 100 = 250 kJ.
MCQ 40
Which of the following represents the First Law of Thermodynamics correctly for a closed system?(MPPSC SI TRANSPORT BOOK )
A) Heat & work are identical
B) Energy can be created
C) Energy balances as ΔU = Q – W
D) Heat cannot be converted to work
Answer: C) ΔU = Q – W
Explanation:
This is the mathematical statement for closed system convention.
MCQ 41
An open system is also called a:(MPPSC SI TRANSPORT BOOK )
A) Control surface
B) Control mass
C) Control volume
D) Isolated system
Answer: C) Control volume
Explanation:
- Mass can cross the boundary in an open system → also called a control volume.
- A closed system is referred to as a control mass.
MCQ 42
The energy associated with mass entering or leaving a control volume is known as:(MPPSC SI TRANSPORT BOOK )
A) Flow energy
B) Heat
C) Work
D) Entropy
Answer: A) Flow energy
Explanation:
Flow energy = p vpv (pressure × specific volume). This represents the energy required to push mass into/out of the control volume.
MCQ 43
The Steady Flow Energy Equation (SFEE) is based on:(MPPSC SI TRANSPORT BOOK )
A) Conservation of momentum
B) Conservation of entropy
C) Conservation of mass and energy
D) Conservation of volume
Answer: C) Conservation of mass and energy
Explanation:
The First Law in open systems applies with mass transfer → SFEE ensures energy is balanced for steady-flow conditions.
MCQ 44
In SFEE, the total energy per unit mass is given as:(MPPSC SI TRANSPORT BOOK )
A) u+pvu+pv
B) h+V22+gzh+2V2+gz
C) u+Vpu+pV
D) Tds+VdPTds+VdP
Answer: B) h+V22+gzh+2V2+gz
Explanation:
Total energy per unit mass = enthalpy + kinetic energy + potential energy.
MCQ 45
For a turbine operating under steady flow, the primary purpose is:(MPPSC SI TRANSPORT BOOK )
A) To increase enthalpy
B) To convert heat into shaft work
C) To convert fluid enthalpy into shaft work
D) To transfer entropy
Answer: C) To convert fluid enthalpy into shaft work
Explanation:
Turbines expand high-enthalpy fluid producing shaft work output.
MCQ 46
For a nozzle, the energy conversion primarily is:(MPPSC SI TRANSPORT BOOK )
A) Heat into work
B) Enthalpy into kinetic energy
C) Kinetic energy into enthalpy
D) Work to heat
Answer: B) Enthalpy into kinetic energy
Explanation:
A nozzle accelerates flow by dropping enthalpy (thermal energy → velocity increase).
MCQ 47
In a diffuser, the energy conversion is:(MPPSC SI TRANSPORT BOOK )
A) Enthalpy → velocity
B) Velocity → enthalpy (pressure rise)
C) Work → heat
D) Heat → work
Answer: B) Velocity → enthalpy (pressure rise)
Explanation:
Diffuser slows down the fluid, increasing pressure/enthalpy.
MCQ 48
The SFEE for a steady flow system is written as:(MPPSC SI TRANSPORT BOOK )
A) Q−W=Δh+ΔV22+ΔgzQ−W=Δh+Δ2V2+Δgz
B) ΔU=Q−WΔU=Q−W
C) TdS=dU+pdVTdS=dU+pdV
D) δQ=δWδQ=δW
Answer: A)
Explanation:
The SFEE is the extension of the First Law to control volume systems.
MCQ 49
In a compressor (steady flow), the work done on the system is mainly to:(MPPSC SI TRANSPORT BOOK )
A) Increase enthalpy
B) Increase entropy
C) Increase potential head
D) Increase kinetic energy
Answer: A) Increase enthalpy
Explanation:
Compression → raises enthalpy (temperature & pressure increase).
MCQ 50
Which term is negligible in most engineering devices like turbines, compressors, boilers?(MPPSC SI TRANSPORT BOOK )
A) Enthalpy
B) Kinetic and potential energies
C) Work
D) Heat transfer
Answer: B) Kinetic and potential energies
Explanation:
These are often very small compared to enthalpy changes and work interactions.
MCQ 51
The steady flow assumption implies:(MPPSC SI TRANSPORT BOOK )
A) Properties vary with time
B) Properties do not vary with time at a fixed location
C) No flow of mass
D) Energy is not conserved
Answer: B) Properties do not vary with time at a fixed location
Explanation:
Steady flow means inlet/outlet mass flow and energy remain constant with time.
MCQ 52
In boilers, heat transfer at steady flow mainly increases:(MPPSC SI TRANSPORT BOOK )
A) Kinetic energy
B) Pressure energy
C) Enthalpy of the fluid
D) Potential energy
Answer: C) Enthalpy of the fluid
Explanation:
Boilers transfer heat into water/steam → enthalpy increases.
MCQ 53
Which of the following devices produces shaft work under steady-flow conditions?(MPPSC SI TRANSPORT BOOK )
A) Nozzle
B) Turbine
C) Boiler
D) Diffuser
Answer: B) Turbine
Explanation:
Turbines expand high-pressure working fluid → deliver mechanical work.
MCQ 54
In a throttling device, which property remains constant ideally?(MPPSC SI TRANSPORT BOOK )
A) Enthalpy
B) Entropy
C) Pressure
D) Internal energy
Answer: A) Enthalpy
Explanation:
Throttling = adiabatic, no work, negligible KE/PE changes → hin=houthin=hout.
MCQ 55
For a heat exchanger, which is usually negligible in energy balance?(MPPSC SI TRANSPORT BOOK )
A) Heat transfer
B) Work transfer
C) Mass transfer
D) Enthalpy transfer
Answer: B) Work transfer
Explanation:
Heat exchangers mainly exchange energy via enthalpy change; no shaft work.
MCQ 56
In the first law for open systems, the term pVpV is included because:(MPPSC SI TRANSPORT BOOK )
A) It represents kinetic energy
B) It represents flow work
C) It represents potential energy
D) It represents random energy
Answer: B) It represents flow work
Explanation:
Flow work needed to push fluid into/out of control volume.
MCQ 57
For a pump, the work done per unit mass of fluid is:(MPPSC SI TRANSPORT BOOK )
A) Increase in kinetic energy
B) Increase in potential energy
C) Increase in enthalpy
D) Loss of entropy
Answer: C) Increase in enthalpy
Explanation:
Pumps raise fluid pressure (hence enthalpy) by work input.
MCQ 58
The SFEE for adiabatic turbine neglecting KE/PE terms reduces to:(MPPSC SI TRANSPORT BOOK )
A) W=hin−houtW=hin−hout
B) W=ΔUW=ΔU
C) Δh=ΔQΔh=ΔQ
D) Q=WQ=W
Answer: A) W=hin−houtW=hin−hout
Explanation:
Adiabatic turbine: heat ≈ 0, so work = enthalpy drop.
MCQ 59
If a nozzle accelerates steam from 30 m/s to 300 m/s, the increase in kinetic energy per unit mass is:(MPPSC SI TRANSPORT BOOK )
A) 4.5 kJ/kg
B) 450 kJ/kg
C) 45 kJ/kg
D) 0.45 kJ/kg
Answer: A) 4.5 kJ/kg
Explanation:
ΔKE = (V₂² – V₁²)/2 = (300² – 30²)/2 = (90000 – 900)/2 = 89100/2 = 44550 J/kg ≈ 44.55 kJ/kg ~ 45 kJ/kg.
Correct choice = C) 45 kJ/kg (typo fixed).
MCQ 60
In a nozzle test, enthalpy decreases from 2800 kJ/kg to 2600 kJ/kg. If KE at exit neglecting inlet velocity is considered, the exit velocity is:(MPPSC SI TRANSPORT BOOK )
A) 200 m/s
B) 400 m/s
C) 600 m/s
D) 800 m/s
Answer: B) 400 m/s
Explanation:
Δh = 200 kJ/kg = 200,000 J/kg = KE gain = V²/2.
So V = √(2 × 200,000) = √400,000 = 632 m/s (approx).
Closest option = C) 600 m/s.
MCQ 61
An Internal Combustion (IC) engine is an example of what kind of thermodynamic system?(MPPSC SI TRANSPORT BOOK )
A) Closed system
B) Open system (cyclic)
C) Isolated system
D) Adiabatic system
Answer: B) Open system
Explanation:
IC engines continuously exchange mass (air-fuel mixture, exhaust gases) and energy → open system analysis.
MCQ 62
The air standard cycle of a spark ignition (SI) engine is:(MPPSC SI TRANSPORT BOOK )
A) Diesel cycle
B) Dual cycle
C) Otto cycle
D) Stirling cycle
Answer: C) Otto cycle
Explanation:
SI engines are modeled by the Otto cycle (constant-volume heat addition).
MCQ 63
The air standard cycle for compression ignition (CI) engines is:(MPPSC SI TRANSPORT BOOK )
A) Brayton cycle(MPPSC SI TRANSPORT BOOK )
B) Otto cycle
C) Diesel cycle
D) Ericsson cycle
Answer: C) Diesel cycle
Explanation:
CI engines are modeled by Diesel cycle (constant-pressure heat addition).
MCQ 64
The ideal cycle efficiency depends primarily on:(MPPSC SI TRANSPORT BOOK )
A) Type of working substance
B) Compression ratio
C) Heat input
D) Initial pressure
Answer: B) Compression ratio
Explanation:
For both Otto & Diesel cycles, efficiency ∝ compression ratio (r).
MCQ 65
The efficiency of the Otto cycle is given by:(MPPSC SI TRANSPORT BOOK )
A) η=1−1rγ−1η=1−rγ−11
B) η=1−T1T2η=1−T2T1
C) η=WQinη=QinW
D) η=1−1γrη=1−γr1
Answer: A) η=1−1rγ−1η=1−rγ−11
Explanation:
Where rr = compression ratio, γγ = ratio of specific heats.
MCQ 66
The Diesel cycle efficiency formula is:(MPPSC SI TRANSPORT BOOK )
A) η=1−1rγ−1η=1−rγ−11
B) η=1−1rγ−1⋅ργ−1γ(ρ−1)η=1−rγ−11⋅γ(ρ−1)ργ−1
C) η=1−T1T2η=1−T2T1
D) η=ργ−1−1γ(ρ−1)η=γ(ρ−1)ργ−1−1
Answer: B)
Explanation:
Diesel efficiency depends on both compression ratio (r) and cut-off ratio (ρ).
MCQ 67
Which cycle has higher efficiency for the same compression ratio?(MPPSC SI TRANSPORT BOOK )
A) Otto cycle
B) Diesel cycle
C) Dual cycle
D) Brayton cycle
Answer: A) Otto cycle
Explanation:
Since heat is added at constant volume, Otto cycle is more efficient at same compression ratio.
MCQ 68
The maximum pressure in an Otto cycle occurs at the:(MPPSC SI TRANSPORT BOOK )
A) Beginning of compression
B) End of compression
C) Beginning of expansion
D) End of expansion
Answer: C) Beginning of expansion
Explanation:
After combustion (constant volume heat addition), pressure peaks before expansion.
MCQ 69
The cut-off ratio (ρ) in Diesel cycle is defined as:(MPPSC SI TRANSPORT BOOK )
A) ρ=V1V2ρ=V2V1
B) ρ=V3V2ρ=V2V3
C) ρ=V4V1ρ=V1V4
D) ρ=T3T2ρ=T2T3
Answer: B) ρ=V3V2ρ=V2V3
Explanation:
ρ = cutoff ratio = ratio of cylinder volume after & before combustion at constant pressure.
MCQ 70
The compression ratio of an engine is given by:(MPPSC SI TRANSPORT BOOK )
A) r=VcVsr=VsVc
B) r=V1V2r=V2V1
C) r=P1P2r=P2P1
D) r=T2T1r=T1T2
Answer: B) r=VmaxVmin=V1V2r=VminVmax=V2V1
Explanation:
Compression ratio = (clearance volume + swept volume) / clearance volume.
MCQ 71
Which of the following gives maximum work output for IC engine cycles?(MPPSC SI TRANSPORT BOOK )
A) Otto cycle
B) Diesel cycle
C) Dual cycle
D) Carnot cycle
Answer: D) Carnot cycle
Explanation:
Though not practical, the Carnot cycle gives max possible efficiency for given T-limits.
MCQ 72
In SI engines, knocking tendency decreases with:(MPPSC SI TRANSPORT BOOK )
A) Increasing compression ratio
B) Increasing octane number
C) High inlet temperature
D) Advanced spark timing
Answer: B) Increasing octane number
Explanation:
Octane rating is resistance to knocking → high octane fuels are knock-resistant.
MCQ 73
The fuel property that characterizes knocking in CI engines is:(MPPSC SI TRANSPORT BOOK )
A) Cetane number
B) Octane number
C) Flash point
D) Volatility
Answer: A) Cetane number
Explanation:
Cetane number = ignition quality of diesel fuels.
MCQ 74
In the p–V diagram of the Diesel cycle, the 2 → 3 process is:(MPPSC SI TRANSPORT BOOK )
A) Isothermal
B) Constant volume
C) Constant pressure
D) Isentropic
Answer: C) Constant pressure
Explanation:
Diesel cycle adds heat at constant pressure.
MCQ 75
Which thermodynamic process models the compression stroke in both Otto and Diesel cycles?(MPPSC SI TRANSPORT BOOK )
A) Isothermal
B) Isobaric
C) Isentropic
D) Isothermal + isentropic
Answer: C) Isentropic
Explanation:
Compression in ideal analysis → reversible adiabatic (isentropic).
MCQ 76
Which of the following best represents the expansion stroke in IC engine cycles?(MPPSC SI TRANSPORT BOOK )
A) Adiabatic expansion
B) Isothermal expansion
C) Constant pressure expansion
D) Constant volume expansion
Answer: A) Adiabatic expansion
Explanation:
Power stroke expansion is approximated as a reversible adiabatic (isentropic) expansion.
MCQ 77
The Dual cycle is a combination of:(MPPSC SI TRANSPORT BOOK )
A) Otto + Carnot
B) Otto + Diesel
C) Brayton + Otto
D) Diesel + Carnot
Answer: B) Otto + Diesel
Explanation:
Dual cycle has heat addition at constant volume & constant pressure → hybrid.
MCQ 78
Mean effective pressure (MEP) of a cycle is defined as:(MPPSC SI TRANSPORT BOOK )
A) Average pressure on piston during only compression
B) Average pressure on piston during only expansion
C) Hypothetical constant pressure giving the same work over stroke
D) Maximum pressure inside the cylinder
Answer: C)
Explanation:
MEP = constant pressure that would produce the same work as the actual cycle.
MCQ 79
The work per cycle in IC engines can be estimated by:(MPPSC SI TRANSPORT BOOK )
A) Area under T–S diagram
B) Area under P–V diagram
C) Area under h–s diagram
D) Area under P–T diagram
Answer: B) Area under P–V diagram
Explanation:
Work = ∮ PdV → represented by the enclosed diagram area.
MCQ 80
For the same compression ratio and heat input, the correct order of cycle efficiencies is:(MPPSC SI TRANSPORT BOOK )
A) Otto > Diesel > Dual
B) Diesel > Otto > Dual
C) Otto > Dual > Diesel
D) Dual > Otto > Diesel
Answer: C) Otto > Dual > Diesel
Explanation:
- For a given r:
- Otto cycle most efficient,
- Diesel least efficient (due to cutoff),
MCQ 81
Which property is a measure of the “quality of energy” available for work?(MPPSC SI TRANSPORT BOOK )
A) Energy
B) Enthalpy
C) Entropy
D) Exergy
Answer: D) Exergy
Explanation:
Exergy represents the maximum useful work possible from a system relative to its environment.
MCQ 82
An isolated system always has:(MPPSC SI TRANSPORT BOOK )
A) ΔU = Q – W
B) No heat and no work transfer
C) Constant temperature only
D) Entropy always decreases
Answer: B) No heat and no work transfer
Explanation:
Isolated = no energy or mass exchange. Only internal transformations occur.
MCQ 83
In an adiabatic process, if work is done on the system then:(MPPSC SI TRANSPORT BOOK )
A) Internal energy decreases
B) Internal energy increases
C) Temperature decreases
D) Heat increases
Answer: B) Internal energy increases
Explanation:
Q = 0. Work done on system increases ΔU, raising T.
MCQ 84
Equation for polytropic process is:(MPPSC SI TRANSPORT BOOK )
A) PV=CPV=C
B) PVn=CPVn=C
C) P/T=P/T= constant
D) PVγ=CPVγ=C
Answer: B) PVn=CPVn=C
Explanation:
General process law, where n = polytropic index (for isothermal n=1, adiabatic n=γ).
MCQ 85
In a reversible adiabatic (isentropic) process, entropy change is:(MPPSC SI TRANSPORT BOOK )
A) Zero
B) Positive
C) Negative
D) Infinite
Answer: A) Zero
Explanation:
Isentropic = no entropy change.
MCQ 86
Which IC engine cycle gives the highest efficiency when compared at the same maximum pressure and temperature?(MPPSC SI TRANSPORT BOOK )
A) Otto
B) Diesel
C) Dual
D) Carnot
Answer: D) Carnot
Explanation:
Carnot is the theoretical upper limit for efficiency between two temperatures.
MCQ 87
Why is the Carnot cycle not suitable for IC engines?(MPPSC SI TRANSPORT BOOK )
A) Requires isothermal compression and expansion
B) Needs very high compression ratios
C) Cycle time is infinite
D) All of the above
Answer: D) All of the above
Explanation:
Isothermal processes and infinite heat exchangers make Carnot impractical.
MCQ 88
The relation between work and heat for a closed system undergoing a cycle is:(MPPSC SI TRANSPORT BOOK )
A) Net heat = Net work
B) Net work = Change in internal energy
C) Net heat = Change in enthalpy
D) Work = Heat × Entropy
Answer: A) Net heat = Net work
Explanation:
From 1st law over a cycle: ΔU = 0 ⇒ Q_net = W_net.
MCQ 89
In IC engines, the indicated power is obtained from:(MPPSC SI TRANSPORT BOOK )
A) Shaft work measured
B) Brake power + Friction power
C) p–V indicator diagram
D) Heat supplied × efficiency
Answer: C) p–V indicator diagram
Explanation:
The area of the indicator diagram gives indicated work per cycle.
MCQ 90
Brake Power (BP) is always:(MPPSC SI TRANSPORT BOOK )
A) Equal to Indicated Power
B) Greater than Indicated Power
C) Less than Indicated Power
D) Equal to Friction Power
Answer: C) Less than Indicated Power
Explanation:
Because frictional losses reduce the brake output power relative to indicated power.
MCQ 91
Friction Power (FP) in an IC engine is:(MPPSC SI TRANSPORT BOOK )
A) BP – IP
B) IP – BP
C) IP + BP
D) Zero
Answer: B) FP = IP – BP
Explanation:
Loss due to mechanical friction, pumping, auxiliaries in the engine.
MCQ 92
Which is the correct efficiency relationship?(MPPSC SI TRANSPORT BOOK )
A) η_mech = BP/IP
B) η_thermal = IP/Q_input
C) η_overall = BP/Q_input
D) All of the above
Answer: D) All of the above
Explanation:
Different efficiencies: mechanical (BP vs IP), thermal (IP vs Q), and overall (BP vs Q).
MCQ 93
For a 4-stroke engine, the number of power strokes per crankshaft revolution is:(MPPSC SI TRANSPORT BOOK )
A) 1
B) 2
C) 0.5
D) 4
Answer: C) 0.5
Explanation:
One power stroke occurs in 2 revolutions → 1/2 = 0.5 per revolution.
MCQ 94
For a 2-stroke engine, the number of power strokes per crankshaft revolution is:(MPPSC SI TRANSPORT BOOK )
A) 1
B) 0.5
C) 2
D) None
Answer: A) 1
Explanation:
In 2-stroke → 1 power stroke for every revolution.
MCQ 95
Volumetric efficiency of an IC engine is defined as:(MPPSC SI TRANSPORT BOOK )
A) Ratio of swept volume to clearance volume
B) Ratio of actual volume of air intake to swept volume
C) Ratio of mass of air actually drawn to mass theoretically possible
D) Ratio of indicated work to heat input
Answer: C)
Explanation:
Volumetric efficiency measures breathing ability of the engine.
MCQ 96
Which efficiency is always higher in CI engines compared to SI engines (for the same compression ratio)?(MPPSC SI TRANSPORT BOOK )
A) Mechanical efficiency
B) Indicated thermal efficiency
C) Overall efficiency
D) Volumetric efficiency
Answer: B) Indicated thermal efficiency
Explanation:
Diesel cycle has higher efficiency because CI engines operate at higher compression ratios.
MCQ 97
Supercharging in IC engines improves:(MPPSC SI TRANSPORT BOOK )
A) Compression ratio
B) Mass flow and power output
C) Clearance volume
D) Compression work only
Answer: B) Mass flow and power output
Explanation:
Superchargers/deliver more air-fuel mix per cycle → higher power.
MCQ 98
If the compression ratio of an Otto cycle engine increases:(MPPSC SI TRANSPORT BOOK )
A) Efficiency increases
B) Efficiency decreases
C) Efficiency remains constant
D) Efficiency becomes zero
Answer: A) Efficiency increases
Explanation:
Otto efficiency ∝ compression ratio (r). Higher r → higher efficiency.
MCQ 99
The calorific value of a fuel is measured using:(MPPSC SI TRANSPORT BOOK )
A) Bomb calorimeter
B) Pyrometer
C) Anemometer
D) Planimeter
Answer: A) Bomb calorimeter
Explanation:
Bomb calorimeter determines heating value of fuels.
MCQ 100
Among Otto, Diesel, and Dual cycles, which has maximum work output for same compression ratio and heat input?(MPPSC SI TRANSPORT BOOK )
A) Otto
B) Diesel
C) Dual
D) Carnot
Answer: A) Otto
Explanation:
At same compression ratio, Otto has the highest efficiency; Carnot is the limit, but not practical.