100 Important MCQs (Set-1 Basic Level) on Heat and Thermodynamics, Physics (Unit-Wise MCQs Practice):
This post contains 100 carefully selected multiple-choice questions (MCQs) (Set-1 Basic Level) on the unit of Physics: Heat and Thermodynamics, designed according to all board exams syllabus. These MCQs include a well-balanced mix of conceptual and numerical problems, making them exam-ready, revision-friendly, and high-scoring for students.
Whether you are preparing for annual board examinations, chapter tests, or competitive entry tests, this comprehensive MCQ collection thoroughly covers all the fundamental principles of thermodynamics, helping students build strong conceptual understanding and problem-solving skills.
This unit-wise 100 MCQ (set- 1 Basic level) on Heat and Thermodynamics includes questions from:
- Concept of thermodynamic systems and surroundings
- Types of systems: open, closed, and isolated systems
- State variables and thermodynamic equilibrium
- Zeroth Law of Thermodynamics and concept of temperature
- Heat, work, and internal energy
- First Law of Thermodynamics and its mathematical expression
- Applications of the First Law in isothermal, isobaric, isochoric, and adiabatic processes
- Thermodynamic processes and P–V diagrams
- Specific heat capacities and calorimetry
- Heat engines and their working principles
- Efficiency of heat engines and Carnot engine
- Second Law of Thermodynamics and its statements
- Reversible and irreversible processes
- Entropy and its physical significance
- Practical applications of thermodynamics in daily life and technology
Each MCQ is provided with the correct answer and a clear, concise explanation, helping students:
- Strengthen their conceptual understanding of heat and energy transfer
- Avoid common mistakes in numerical and conceptual questions
- Improve problem-solving skills in thermodynamics
- Achieve maximum marks in the MCQs section of exams
These 100 Thermodynamics MCQ collection is an essential resource for the students who want to master thermodynamics concepts and score high in physics examinations.
Topic: Heat Transfer & Temperature
MCQs No.1
Thermal energy flows naturally from:
a) Lower temperature to higher temperature
b) Higher temperature to lower temperature
c) Equal temperatures
d) Any direction
Correct Answer is option b. Higher temperature to lower temperature
Explanation: Heat flows from hot to cold until equilibrium is achieved.
Topic: Thermal Equilibrium (Zeroth Law)
2. Two bodies are in thermal equilibrium if they have:
a) Equal pressure
b) Equal temperature
c) Equal volume
d) Equal mass
Correct Answer is option b. Equal temperature
Explanation: No net heat flow occurs when temperatures are equal.
Topic: Heat and Work as Energy Transfer
3. Heat and work are:
a) Forms of matter
b) Forms of energy transfer
c) State variables
d) Mechanical quantities only
Correct Answer is option b. Forms of energy transfer
Explanation: Energy can cross system boundaries as heat or work.
Topic: Definition of Thermodynamics
4. Thermodynamics is the study of:
a) Motion of particles
b) Heat, work, and energy
c) Electricity
d) Nuclear reactions
Correct Answer is option b. Heat, work, and energy
Explanation: Thermodynamics deals with energy transformations.
Topic: Internal Energy Concept
5. Internal energy of a gas is mainly due to:
a) Macroscopic motion
b) Gravitational energy
c) Molecular kinetic and potential energies
d) External work
Correct Answer is option c. Molecular kinetic and potential energies
Explanation: Internal energy arises from random molecular motion and interactions.
Topic: Internal Energy vs Temperature
6. Increase in temperature of a body results in:
a) Decrease in internal energy
b) No change in internal energy
c) Increase in internal energy
d) Zero internal energy
Correct Answer is option c. Increase in internal energy
Explanation: Higher temperature means higher molecular kinetic energy.
Topic: Mechanical Equivalent of Heat
7. Mechanical equivalent of heat relates:
a) Mass and energy
b) Work and heat
c) Pressure and volume
d) Temperature and entropy
Correct Answer is option b. Work and heat
Explanation: It shows how mechanical work converts into heat.
Topic: Work Done by Gas (Isobaric Process)
8. Work done by gas at constant pressure is:
a) Zero
b) PΔV
c) ΔU
d) Q − ΔU
Correct Answer is option b. PΔV
Explanation: For isobaric process, work = pressure × change in volume.
Topic: First Law of Thermodynamics
9. First law of thermodynamics is:
a) ΔU = W − Q
b) ΔU = Q − W
c) ΔU = 0
d) Q = W
Correct Answer is option b. ΔU = Q − W
Explanation: Change in internal energy equals heat added minus work done.
Topic: Conservation of Energy
10. First law of thermodynamics expresses:
a) Entropy law
b) Energy conservation
c) Temperature law
d) Pressure law
Correct Answer is option b. Energy conservation
Explanation: Energy cannot be created or destroyed.
Topic: Numerical (First Law)
11. A gas absorbs 500 J heat and does 200 J work. ΔU = ?
a) 300 J
b) 700 J
c) -300 J
d) 200 J
Correct Answer is option a. 300 J
Explanation: ΔU = 500 − 200 = 300 J.
Topic: Specific Heat
12. Specific heat capacity is heat required to raise temperature of:
a) 1 kg by 1 K
b) 1 g by 1 K
c) 1 mole by 1 K
d) Any mass by 1 K
Correct Answer is option a. 1 kg by 1 K
Explanation: It is defined per unit mass.
Topic: Molar Specific Heat
13. Molar specific heat is heat required to raise temperature of:
a) 1 kg
b) 1 g
c) 1 mole
d) 1 liter
Correct Answer is option c. 1 mole
Explanation: It is defined per mole of substance.
Topic: Cp and Cv Relation
14. For ideal gas, Cp − Cv equals:
a) 0
b) R
c) 2R
d) 1/R
Correct Answer is option b. R
Explanation: This is Mayer’s relation.
Topic: First Law Application
15. For constant volume process, heat added equals:
a) Work done
b) ΔU
c) PΔV
d) Zero
Correct Answer is option b. ΔU
Explanation: No work is done at constant volume.
Topic: Heat Engine Principle
16. A heat engine converts:
a) Work into heat
b) Heat into work
c) Heat into temperature
d) Work into entropy
Correct Answer is option b. Heat into work
Explanation: Heat engines convert thermal energy into mechanical work.
Topic: Reversible Process
17. A reversible process is one that:
a) Happens suddenly
b) Can be reversed without leaving change
c) Always irreversible
d) Occurs with friction
Correct Answer is option b. Can be reversed without leaving change
Explanation: Reversible processes occur infinitely slowly without losses.
Topic: Irreversible Process
18. Free expansion of gas is an example of:
a) Reversible process
b) Isothermal process
c) Irreversible process
d) Adiabatic process
Correct Answer is option c. Irreversible process
Explanation: Free expansion cannot be reversed without external work.
Topic: Second Law of Thermodynamics
19. Second law states that entropy of an isolated system:
a) Decreases
b) Remains constant
c) Increases
d) Becomes zero
Correct Answer is option c. Increases
Explanation: Natural processes increase disorder.
Topic: Carnot Engine
20. Carnot engine is:
a) Real engine
b) Ideal reversible engine
c) Diesel engine
d) Refrigerator
Correct Answer is option b. Ideal reversible engine
Explanation: Carnot engine represents maximum theoretical efficiency.
Topic: Carnot Efficiency
21. Carnot efficiency depends on:
a) Nature of gas
b) Working substance
c) Temperatures of reservoirs
d) Pressure
Correct Answer is option c. Temperatures of reservoirs
Explanation: η = 1 − Tc/Th.
Topic: Refrigerator Concept
22. A refrigerator is a heat engine operating:
a) Normally
b) With zero work
c) In reverse direction
d) At constant temperature
Correct Answer is option c. In reverse direction
Explanation: It removes heat from cold body using work.
Topic: Coefficient of Performance (COP)
23. COP of refrigerator is:
a) W/Qc
b) Qc/W
c) Qh/W
d) W/Qh
Correct Answer is option b. Qc/W
Explanation: It measures cooling efficiency.
Topic: Entropy and Heat
24. Entropy increases when:
a) Heat is removed
b) Heat is added
c) Temperature decreases
d) Volume decreases
Correct Answer is option b. Heat is added
Explanation: Adding heat increases disorder.
Topic: Disorder and Entropy
25. Increase in entropy means:
a) More order
b) Less disorder
c) Energy degradation
d) Energy creation
Correct Answer is option c. Energy degradation
Explanation: Energy becomes less available for useful work.
Topic: Internal Energy as State Function
26. Internal energy of a system is a:
a) Path function
b) State function
c) External variable
d) Vector quantity
Correct Answer is option b. State function
Explanation: Internal energy depends only on the state, not the path.
Topic: Internal Energy (Ideal Gas)
27. For an ideal gas, internal energy depends on:
a) Pressure
b) Volume
c) Temperature only
d) Density
Correct Answer is option c. Temperature only
Explanation: For ideal gas, U is a function of temperature.
Topic: Work Done (General Concept)
28. Work done by a gas during expansion is equal to:
a) ΔU
b) PΔV
c) Q
d) mgh
Correct Answer is option b. PΔV
Explanation: Work is done when volume changes under pressure.
Topic: Isothermal Process
29. In an isothermal process, the temperature of gas:
a) Increases
b) Decreases
c) Remains constant
d) Becomes zero
Correct Answer is option c. Remains constant
Explanation: Isothermal means constant temperature.
Topic: Isochoric Process
30. In an isochoric process, work done is:
a) Maximum
b) Minimum
c) Zero
d) Equal to Q
Correct Answer is option c. Zero
Explanation: Volume is constant, so ΔV = 0, hence W = 0.
Topic: Adiabatic Process
31. In an adiabatic process, heat exchange is:
a) Maximum
b) Minimum
c) Zero
d) Infinite
Correct Answer is option c. Zero
Explanation: Adiabatic means no heat transfer (Q = 0).
Topic: Temperature Change in Adiabatic Expansion
32. During adiabatic expansion, gas temperature:
a) Increases
b) Decreases
c) Remains constant
d) Becomes zero
Correct Answer is option b. Decreases
Explanation: Gas does work, reducing internal energy and temperature.
Topic: Specific Heat (Cp and Cv)
33. Cp is greater than Cv because:
a) Gas expands at constant pressure
b) Gas compresses
c) Temperature decreases
d) Volume remains constant
Correct Answer is option a. Gas expands at constant pressure
Explanation: Extra heat is required to do expansion work.
Topic: Mayer’s Relation
34. The relation Cp − Cv = R is known as:
a) Boyle’s law
b) Charles’ law
c) Mayer’s relation
d) Carnot law
Correct Answer is option c. Mayer’s relation
Explanation: It relates molar specific heats of ideal gases.
Topic: Degrees of Freedom
35. For a monoatomic gas, Cv equals:
a) R
b) 3/2 R
c) 5/2 R
d) 7/2 R
Correct Answer is option b. 3/2 R
Explanation: Monoatomic gases have 3 translational degrees of freedom.
Topic: Numerical (Internal Energy)
36. One mole of monoatomic gas is heated by 10 K at constant volume. ΔU = ? (R = 8.314 J/mol·K)
a) 124.7 J
b) 83.14 J
c) 166.3 J
d) 41.57 J
Correct Answer is option a. 124.7 J
Explanation: ΔU = nCvΔT = 1 × (3/2 R) × 10.
Topic: Heat Engine Principle
37. A heat engine works between:
a) One reservoir
b) Two reservoirs at same temperature
c) Two reservoirs at different temperatures
d) Three reservoirs
Correct Answer is option c. Two reservoirs at different temperatures
Explanation: Heat must flow from hot to cold reservoir.
Topic: Heat Engine Efficiency
38. Efficiency of heat engine is defined as:
a) Qh/W
b) W/Qh
c) Qc/W
d) Qh/Qc
Correct Answer is option b. W/Qh
Explanation: Efficiency = useful work output / heat absorbed.
Topic: Carnot Efficiency Numerical
39. If Th = 600 K and Tc = 300 K, Carnot efficiency is:
a) 25%
b) 33%
c) 50%
d) 75%
Correct Answer is option c. 50%
Explanation: η = 1 − Tc/Th = 1 − 300/600 = 0.5.
Topic: Reversible Process
40. A reversible process must occur:
a) Rapidly
b) With friction
c) Infinitely slowly
d) With heat loss
Correct Answer is option c. Infinitely slowly
Explanation: It must remain in equilibrium at all times.
Topic: Irreversible Process
41. Which of the following is irreversible?
a) Slow compression
b) Slow expansion
c) Free expansion
d) Quasi-static process
Correct Answer is option c. Free expansion
Explanation: Free expansion cannot be reversed without external changes.
Topic: Refrigerator Concept
42. Refrigerator transfers heat from:
a) Hot to cold body
b) Cold to hot body using work
c) Hot to hot body
d) Cold to cold body
Correct Answer is option b. Cold to hot body using work
Explanation: Work is required to pump heat against natural flow.
Topic: Coefficient of Performance (COP)
43. COP of refrigerator is maximum when:
a) Tc is high and Th is low
b) Tc is low and Th is high
c) Tc and Th are equal
d) Work is zero
Correct Answer is option a. Tc is high and Th is low
Explanation: Smaller temperature difference increases COP.
Topic: Entropy Change
44. Entropy change for heat addition at temperature T is:
a) ΔS = QT
b) ΔS = Q/T
c) ΔS = T/Q
d) ΔS = Q×T
Correct Answer is option b. ΔS = Q/T
Explanation: Entropy change is heat divided by absolute temperature.
Topic: Entropy and Disorder
45. Entropy increases when:
a) Gas is compressed
b) Gas is cooled
c) Gas expands freely
d) Heat is removed
Correct Answer is option c. Gas expands freely
Explanation: Free expansion increases randomness.
Topic: Energy Degradation
46. Energy degradation means energy:
a) Is destroyed
b) Becomes less useful
c) Becomes heat always
d) Becomes zero
Correct Answer is option b. Becomes less useful
Explanation: High-quality energy converts to low-quality heat.
Topic: Natural Processes
47. In all natural processes, entropy:
a) Decreases
b) Remains constant
c) Increases
d) Becomes zero
Correct Answer is option c. Increases
Explanation: Natural processes are irreversible and increase disorder.
Topic: Order of Systems
48. With passage of time, systems tend to become:
a) More orderly
b) Less orderly
c) Perfectly ordered
d) Constantly ordered
Correct Answer is option b. Less orderly
Explanation: Entropy increases with time.
Topic: Numerical (First Law)
49. A system absorbs 800 J heat and does 300 J work. ΔU = ?
a) 500 J
b) 1100 J
c) 300 J
d) 800 J
Correct Answer is option a. 500 J
Explanation: ΔU = Q − W = 800 − 300 = 500 J.
Topic: Numerical (Work Calculation)
50. A gas expands from 1 m³ to 4 m³ at pressure 2×10⁵ Pa. Work done is:
a) 2×10⁵ J
b) 4×10⁵ J
c) 6×10⁵ J
d) 8×10⁵ J
Correct Answer is option c. 6×10⁵ J
Explanation: W = PΔV = 2×10⁵ × (4 − 1) = 6×10⁵ J.
opic: Specific Heat at Constant Pressure
51. Specific heat at constant pressure is denoted by:
a) Cv
b) Cp
c) R
d) U
Correct Answer is option b. Cp
Explanation: Cp is molar specific heat at constant pressure.
Topic: Cp and Cv Relation
52. For an ideal gas, Cp/Cv is called:
a) R
b) γ (gamma)
c) η
d) k
Correct Answer is option b. γ (gamma)
Explanation: γ = Cp/Cv, also called adiabatic index.
Topic: Adiabatic Index
53. For a monoatomic gas, γ is approximately:
a) 1.33
b) 1.4
c) 1.67
d) 2.0
Correct Answer is option c. 1.67
Explanation: γ = 5/3 for monoatomic gases.
Topic: Internal Energy Numerical
54. Two moles of diatomic gas heated by 20 K at constant volume. Cv = 5/2 R. ΔU = ?
a) 415.7 J
b) 831.4 J
c) 1662.8 J
d) 2078.5 J
Correct Answer is option b. 831.4 J
Explanation: ΔU = nCvΔT = 2 × (5/2 × 8.314) × 20.
Topic: Work Done (Isothermal)
55. In isothermal expansion of ideal gas, internal energy change is:
a) Positive
b) Negative
c) Zero
d) Infinite
Correct Answer is option c. Zero
Explanation: For ideal gas, U depends only on temperature, which is constant.
Topic: First Law Application
56. If ΔU = 0 and Q = 200 J, work done is:
a) 200 J
b) 0 J
c) -200 J
d) 400 J
Correct Answer is option a. 200 J
Explanation: From ΔU = Q − W, W = Q.
Topic: Heat Engine Efficiency
57. A heat engine absorbs 800 J and rejects 500 J. Efficiency is:
a) 12.5%
b) 37.5%
c) 50%
d) 62.5%
Correct Answer is option b. 37.5%
Explanation: W = 800 − 500 = 300 J; η = 300/800.
Topic: Carnot Engine Theory
58. Carnot cycle consists of:
a) Two isobaric and two isochoric processes
b) Two isothermal and two adiabatic processes
c) Four isothermal processes
d) Four adiabatic processes
Correct Answer is option b. Two isothermal and two adiabatic processes
Explanation: Carnot cycle is ideal reversible cycle.
Topic: Carnot Efficiency Concept
59. If Tc approaches Th, Carnot efficiency becomes:
a) Maximum
b) Zero
c) Infinite
d) Constant
Correct Answer is option b. Zero
Explanation: η = 1 − Tc/Th → 0 when Tc ≈ Th.
Topic: Refrigerator COP Numerical
60. A refrigerator removes 400 J from cold reservoir using 100 J work. COP = ?
a) 2
b) 3
c) 4
d) 5
Correct Answer is option c. 4
Explanation: COP = Qc/W = 400/100 = 4.
Topic: Second Law (Kelvin-Planck Statement)
61. Kelvin-Planck statement says it is impossible to:
a) Convert work into heat
b) Convert heat completely into work
c) Increase entropy
d) Transfer heat from cold to hot
Correct Answer is option b. Convert heat completely into work
Explanation: No heat engine can be 100% efficient.
Topic: Clausius Statement
62. Clausius statement says it is impossible for heat to flow:
a) From hot to cold
b) From cold to hot without work
c) Between equal temperatures
d) In isolated system
Correct Answer is option b. From cold to hot without work
Explanation: Refrigerator requires work to transfer heat backward.
Topic: Entropy Calculation
63. If 200 J heat is added at 400 K, entropy change is:
a) 0.25 J/K
b) 0.5 J/K
c) 1 J/K
d) 2 J/K
Correct Answer is option b. 0.5 J/K
Explanation: ΔS = Q/T = 200/400.
Topic: Entropy and Temperature
64. For same heat added, entropy change is greater at:
a) High temperature
b) Low temperature
c) Constant temperature
d) Zero temperature
Correct Answer is option b. Low temperature
Explanation: ΔS = Q/T, so smaller T gives larger ΔS.
Topic: Energy Degradation Concept
65. High-grade energy refers to:
a) Random heat
b) Low temperature energy
c) Organized energy like work
d) Entropy
Correct Answer is option c. Organized energy like work
Explanation: Work is high-quality energy.
Topic: Natural Processes
66. Which process is spontaneous?
a) Decrease in entropy
b) Constant entropy
c) Increase in entropy
d) Zero entropy
Correct Answer is option c. Increase in entropy
Explanation: Spontaneous processes increase entropy.
Topic: Work Done Sign Convention
67. When gas does work on surroundings, W is taken as:
a) Positive
b) Negative
c) Zero
d) Infinite
Correct Answer is option a. Positive
Explanation: By physics convention, work done by system is positive.
Topic: Work Done on System
68. When surroundings do work on gas, W is:
a) Positive
b) Negative
c) Zero
d) Maximum
Correct Answer is option b. Negative
Explanation: Work done on system is negative.
Topic: Internal Energy Change
69. If Q = 300 J and W = 500 J, ΔU = ?
a) 200 J
b) -200 J
c) 800 J
d) 0 J
Correct Answer is option b. -200 J
Explanation: ΔU = Q − W = 300 − 500 = −200 J.
Topic: System and Surroundings
70. The universe in thermodynamics consists of:
a) System only
b) Surroundings only
c) System + surroundings
d) Heat only
Correct Answer is option c. System + surroundings
Explanation: Universe includes everything.
Topic: Closed System
71. A closed system can exchange:
a) Mass only
b) Energy only
c) Both mass and energy
d) Neither mass nor energy
Correct Answer is option b. Energy only
Explanation: Mass is fixed but energy exchange is allowed.
Topic: Isolated System
72. An isolated system exchanges:
a) Energy only
b) Mass only
c) Both mass and energy
d) Neither mass nor energy
Correct Answer is option d. Neither mass nor energy
Explanation: Isolated system is completely sealed.
Topic: Open System
73. An open system can exchange:
a) Mass only
b) Energy only
c) Both mass and energy
d) Neither
Correct Answer is option c. Both mass and energy
Explanation: Open system interacts freely with surroundings.
Topic: Zeroth Law Application
74. If A is in thermal equilibrium with B and B with C, then A is in equilibrium with C. This is:
a) First law
b) Second law
c) Zeroth law
d) Boyle’s law
Correct Answer is option c. Zeroth law
Explanation: It defines temperature concept.
Topic: Temperature and Internal Energy
75. Doubling absolute temperature of ideal gas (constant volume) will:
a) Double internal energy
b) Halve internal energy
c) Make U zero
d) Not affect U
Correct Answer is option a. Double internal energy
Explanation: U ∝ T for ideal gas.
Topic: Work Calculation Numerical
76. A gas expands from 3 m³ to 7 m³ at pressure 5×10⁵ Pa. Work done = ?
a) 2×10⁶ J
b) 4×10⁶ J
c) 5×10⁶ J
d) 1×10⁶ J
Correct Answer is option b. 4×10⁶ J
Explanation: W = PΔV = 5×10⁵ × 4.
Topic: Heat Engine Concept
77. Heat engine rejects heat to:
a) Hot reservoir
b) Cold reservoir
c) System
d) Surroundings only
Correct Answer is option b. Cold reservoir
Explanation: Waste heat must be rejected to cold sink.
Topic: Maximum Efficiency
78. Maximum efficiency of any engine is less than 100% because of:
a) First law
b) Second law
c) Boyle’s law
d) Charles’ law
Correct Answer is option b. Second law
Explanation: Entropy must increase, so some heat is wasted.
Topic: Entropy and Order
79. A perfectly ordered crystal at absolute zero has entropy:
a) Maximum
b) Infinite
c) Zero
d) Negative
Correct Answer is option c. Zero
Explanation: Third law states entropy is zero at 0 K.
Topic: Energy Transformation
80. Conversion of work into heat is:
a) Impossible
b) Possible and complete
c) Against second law
d) Reversible only
Correct Answer is option b. Possible and complete
Explanation: Work can be fully converted into heat.
Topic: Irreversibility
81. Which increases entropy most?
a) Reversible expansion
b) Slow compression
c) Free expansion
d) Isothermal compression
Correct Answer is option c. Free expansion
Explanation: Free expansion is highly irreversible.
Topic: Refrigerator Efficiency
82. COP of refrigerator becomes zero when:
a) Tc = Th
b) Tc < Th
c) Th > Tc
d) Work is maximum
Correct Answer is option a. Tc = Th
Explanation: No heat can be removed if both reservoirs are same temperature.
Topic: Entropy Sign
83. When heat is removed from a system, entropy change is:
a) Positive
b) Negative
c) Zero
d) Infinite
Correct Answer is option b. Negative
Explanation: Removing heat reduces disorder.
Topic: Energy Degradation
84. In all natural processes, high-grade energy changes into:
a) Work
b) Mechanical energy
c) Low-grade heat
d) Nuclear energy
Correct Answer is option c. Low-grade heat
Explanation: Energy becomes less useful.
Topic: Internal Energy Numerical
85. One mole of monoatomic gas heated 30 K at constant volume. ΔU = ?
a) 124.7 J
b) 249.4 J
c) 374.1 J
d) 498.8 J
Correct Answer is option c. 374.1 J
Explanation: ΔU = 1 × (3/2 × 8.314) × 30.
Topic: Work and Heat Transfer
86. Heat transfer occurs due to:
a) Pressure difference
b) Volume difference
c) Temperature difference
d) Density difference
Correct Answer is option c. Temperature difference
Explanation: Heat flows due to temperature gradient.
Topic: State Variables
87. Which is NOT a state variable?
a) Pressure
b) Volume
c) Temperature
d) Work
Correct Answer is option d. Work
Explanation: Work depends on path.
Topic: Entropy and Disorder
88. Which system has highest entropy?
a) Solid
b) Liquid
c) Gas
d) Crystal at 0 K
Correct Answer is option c. Gas
Explanation: Gas molecules are most disordered.
Topic: Heat Engine Output
89. Work done by heat engine equals:
a) Qh + Qc
b) Qh − Qc
c) Qc − Qh
d) Qh × Qc
Correct Answer is option b. Qh − Qc
Explanation: Work is difference between absorbed and rejected heat.
Topic: Refrigerator Work
90. Work input to refrigerator equals:
a) Qh − Qc
b) Qc − Qh
c) Qh + Qc
d) Zero
Correct Answer is option a. Qh − Qc
Explanation: Work = heat rejected − heat absorbed.
Topic: Carnot Engine Independence
91. Carnot efficiency is independent of:
a) Temperature
b) Pressure
c) Working substance
d) Reservoirs
Correct Answer is option c. Working substance
Explanation: Depends only on Th and Tc.
Topic: Disorder with Temperature
92. Increasing temperature of a system generally:
a) Decreases entropy
b) Increases entropy
c) No effect
d) Makes entropy zero
Correct Answer is option b. Increases entropy
Explanation: Higher temperature increases molecular randomness.
Topic: Entropy Law
93. Entropy of universe:
a) Always decreases
b) Always increases
c) Remains constant
d) Becomes zero
Correct Answer is option b. Always increases
Explanation: Total entropy of universe increases.
Topic: Thermodynamic Cycle
94. In a cyclic process, change in internal energy is:
a) Maximum
b) Minimum
c) Zero
d) Infinite
Correct Answer is option c. Zero
Explanation: System returns to initial state.
Topic: Cyclic Process Work
95. In cyclic process, net work done equals:
a) Change in internal energy
b) Zero
c) Net heat supplied
d) Entropy change
Correct Answer is option c. Net heat supplied
Explanation: ΔU = 0, so Q = W.
Topic: Efficiency Comparison
96. Carnot engine efficiency compared to real engines is:
a) Lower
b) Equal
c) Higher
d) Zero
Correct Answer is option c. Higher
Explanation: Carnot engine is ideal and maximum efficiency.
Topic: Entropy and Order
97. A highly ordered system has:
a) High entropy
b) Low entropy
c) Infinite entropy
d) No entropy
Correct Answer is option b. Low entropy
Explanation: Order means less randomness.
Topic: Thermodynamic Processes
98. In which process no work is done?
a) Isothermal
b) Isobaric
c) Isochoric
d) Adiabatic
Correct Answer is option c. Isochoric
Explanation: Volume is constant, so W = 0.
Topic: Heat and Internal Energy
99. When gas is compressed adiabatically, its internal energy:
a) Decreases
b) Increases
c) Remains constant
d) Becomes zero
Correct Answer is option b. Increases
Explanation: Work done on gas increases internal energy and temperature.
Topic: Entropy Direction
100. Direction of spontaneous process is determined by:
a) Energy
b) Work
c) Entropy
d) Pressure
Correct Answer is option c. Entropy
Explanation: Processes occur in direction of increasing entropy.
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