⭐ Heat, Thermodynamics & Energy – Full GK Guide (1500+ Words)
Heat and Thermodynamics form one of the most scoring chapters in physics. These topics explain how energy flows, how machines work, how engines convert fuel to work, and how the universe naturally moves toward disorder (entropy).
This article includes:
Definitions of Heat & Temperature
Laws of Thermodynamics
Heat Transfer
Energy Forms
Work, Heat & Internal Energy
Real-life applications
50 GK questions with explanations
Perfect for SSC, Railway, Banking, UPSC, CDS, NDA, State Exams, and Class 6–12.
🔥 What is Heat?
Heat is the energy transferred between two objects due to temperature difference.
Key Points:
Heat flows from hot body → cold body
Measured in Joules (J)
Also measured in Calories
🌡️ What is Temperature?
Temperature is the measure of the degree of hotness or coldness of a body.
Temperature Scales:
Celsius (°C)
Fahrenheit (°F)
Kelvin (K) → SI unit
⚖️ Difference Between Heat and Temperature
| Heat | Temperature |
|---|---|
| Energy in transit | Measure of hotness |
| Measured in Joules | Measured in Kelvin |
| Depends on mass | Independent of mass |
| Can be gained or lost | Indicates direction of heat flow |
🔥 Heat Transfer: 3 Methods
1. Conduction
Transfer through solids.
Example: Metal spoon getting hot.
2. Convection
Transfer through liquids & gases.
Example: Boiling water, hot air balloon.
3. Radiation
Transfer without medium.
Example: Sunlight.
⚙️ What is Thermodynamics?
Thermodynamics is the branch of physics dealing with heat, work, energy, and the laws that govern them.
🔺 Laws of Thermodynamics
1️⃣ Zeroth Law:
If A = B in temperature, and B = C, then A = C.
Explains temperature measurement.
2️⃣ First Law of Thermodynamics
Energy can neither be created nor destroyed; only transformed.
Formula:
ΔU = Q – W
(Internal energy = heat added – work done)
3️⃣ Second Law of Thermodynamics
Heat naturally flows from hot to cold.
Entropy (disorder) always increases.
Meaning:
Reverse heat flow is impossible without external energy
Engine efficiency can never be 100%
4️⃣ Third Law of Thermodynamics
Entropy becomes zero as temperature approaches absolute zero (0 K).
⚡ What is Energy?
Energy is the capacity to do work.
Types of Energy:
Mechanical (Kinetic & Potential)
Heat energy
Electrical energy
Chemical energy
Nuclear energy
Sound energy
Light energy
🔋 Work, Heat & Internal Energy
Work (W): Force × displacement
Heat (Q): Energy transfer due to temperature difference
Internal Energy (U): Total energy of particles inside a system
🔥 Specific Heat Capacity
Amount of heat needed to raise 1 kg of a substance by 1°C.
High specific heat → heats slowly (water)
Low specific heat → heats quickly (metal)
🌡️ Latent Heat
Heat absorbed or released without temperature change.
Types:
Latent heat of fusion (solid → liquid)
Latent heat of vaporization (liquid → gas)
🌬️ Thermal Expansion
Materials expand on heating, contract on cooling.
Examples:
Railway tracks have gaps
Electric wires sag in summer
Bridges use expansion joints
🔥 Real-Life Applications of Thermodynamics
Refrigerator
Air conditioner
Heat engine
Steam turbine
Automobile engine
Power plants
⭐ 50 Heat, Thermodynamics & Energy GK Questions with Answers
1. What is the SI unit of heat?
Answer: Joule
2. What is the SI unit of temperature?
Answer: Kelvin
3. What is latent heat?
Answer: Heat absorbed/released without temperature change.
4. What is the Zeroth Law about?
Answer: Thermal equilibrium.
5. What is entropy?
Answer: Measure of disorder.
6. Which law says “energy can’t be created or destroyed”?
Answer: First Law of Thermodynamics.
7. What is conduction?
Answer: Heat transfer through solids.
8. What is convection?
Answer: Heat transfer through fluids.
9. What is radiation?
Answer: Heat transfer without medium.
10. What is Kelvin scale used for?
Answer: Absolute temperature measurement.
11. What is internal energy?
Answer: Total energy of particles in a system.
12. What is heat engine?
Answer: Converts heat into mechanical work.
13. What is Carnot engine?
Answer: Ideal heat engine with maximum efficiency.
14. Who formulated the gas laws?
Answer: Boyle & Charles.
15. What is Boyle’s law?
Answer: Pressure ∝ 1/Volume.
16. What is Charles’s law?
Answer: Volume ∝ Temperature.
17. What is thermal expansion?
Answer: Increase in size when heated.
18. What is specific heat?
Answer: Heat required to raise temperature by 1°C.
19. What is conduction best in?
Answer: Metals.
20. Why do metals get hot quickly?
Answer: Free electrons.
21. What is the boiling point of water?
Answer: 100°C
22. What is the freezing point of water?
Answer: 0°C
23. What is a thermostat used for?
Answer: Regulating temperature.
24. Why does ice float on water?
Answer: Density decreases on freezing.
25. Which gas has highest specific heat?
Answer: Hydrogen.
26. What is absolute zero?
Answer: 0 Kelvin (-273°C).
27. What is adiabatic process?
Answer: No heat exchange.
28. What is isothermal process?
Answer: Temperature constant.
29. What is isobaric process?
Answer: Pressure constant.
30. What is isochoric process?
Answer: Volume constant.
31. What is thermal conductivity?
Answer: Ability to conduct heat.
32. Which color absorbs most heat?
Answer: Black.
33. Why do houses have white roofs?
Answer: Reflect heat.
34. What is solar energy?
Answer: Sunlight energy.
35. What is geothermal energy?
Answer: Heat from Earth’s interior.
36. What is nuclear energy?
Answer: Energy from atomic reactions.
37. What is chemical energy?
Answer: Stored in chemical bonds.
38. What is potential energy?
Answer: Energy due to position.
39. What is kinetic energy?
Answer: Energy due to motion.
40. What is work?
Answer: Force × displacement.
41. What is power?
Answer: Work per unit time (W/t).
42. Why does hot air rise?
Answer: Lower density.
43. What is conduction prevented by?
Answer: Insulators.
44. What is convection prevented by?
Answer: Vacuum (no medium).
45. Which planetary process drives weather?
Answer: Heat transfer.
46. What is greenhouse effect?
Answer: Trapping of heat in atmosphere.
47. What is calorimeter?
Answer: Measures heat.
48. What is the second law of thermodynamics?
Answer: Entropy always increases.
49. Which law explains refrigerator?
Answer: Second law.
50. What is heat capacity?
Answer: Amount of heat needed to raise total temperature by 1°C.
51. What is thermal equilibrium?
Answer: When two bodies have the same temperature.
Explanation: No heat flows between them.
52. What is calorimetry?
Answer: Study of measurement of heat.
Explanation: Done using a calorimeter.
53. What is heat death of the universe?
Answer: A theoretical state where no thermodynamic energy remains.
54. What is thermal resistance?
Answer: Material’s resistance to heat flow.
55. Which has higher thermal conductivity—metal or wood?
Answer: Metal.
Explanation: Metals have free electrons.
56. Why do liquids boil faster at high altitude?
Answer: Lower atmospheric pressure reduces boiling point.
57. What is the heat capacity of a body?
Answer: Heat required to raise its temperature by 1°C.
58. Why does sweat cool your body?
Answer: Evaporation absorbs heat from skin.
59. What is thermal radiation?
Answer: Radiation emitted due to body temperature.
60. Which law governs radiation?
Answer: Stefan-Boltzmann Law.
61. What is emissivity?
Answer: Ability of a surface to emit heat radiation.
62. Perfect absorber of heat is called?
Answer: Black body.
63. Perfect emitter of heat is called?
Answer: Black body.
64. What is black-body radiation?
Answer: Radiation emitted by a perfect black body.
65. Who explained black-body radiation?
Answer: Max Planck.
66. What is Wien’s displacement law?
Answer: Hotter objects emit radiation of shorter wavelength.
67. What is thermal insulation?
Answer: Preventing heat transfer.
Example: Thermos flask.
68. What is conduction coefficient?
Answer: Measure of a material’s heat conduction ability.
69. Why does metal feel cold at room temperature?
Answer: It conducts heat away from skin quickly.
70. Why are woolen clothes warm?
Answer: Wool traps air → insulator.
71. What is adiabatic cooling?
Answer: Cooling due to expansion of gases.
72. What is adiabatic heating?
Answer: Heating due to compression of gases.
73. Why does a bicycle pump become warm?
Answer: Air compression (adiabatic heating).
74. Why does ice melt even at room temperature?
Answer: Absorbs heat from surroundings.
75. Why does hot water freeze faster than cold water?
Answer: Mpemba Effect.
76. Why do pressure cookers cook faster?
Answer: High pressure raises boiling point of water.
77. Why does boiling water have constant temperature?
Answer: Latent heat of vaporization.
78. Why does ice remain at 0°C while melting?
Answer: Latent heat of fusion.
79. What are endothermic processes?
Answer: Absorb heat.
Examples: Melting, evaporation.
80. What are exothermic processes?
Answer: Release heat.
Examples: Freezing, condensation.
81. What is mechanical equivalent of heat?
Answer: Relationship between mechanical work & heat.
Discovered by: James Joule.
82. Why are cooking utensils made of metal?
Answer: Good conductors of heat.
83. Why are handles of utensils made of plastic/wood?
Answer: Poor conductors (insulators).
84. What is convection current?
Answer: Hot fluid rises, cool fluid sinks.
85. Why does smoke go upward?
Answer: Hot air rises (convection).
86. What is heat exchanger?
Answer: Device to transfer heat between two fluids.
Example: AC, refrigerator.
87. Why does metal expand on heating?
Answer: Increase in kinetic energy of atoms.
88. What is coefficient of linear expansion?
Answer: How much a material expands per degree rise in temperature.
89. Why do railway tracks have gaps?
Answer: To allow expansion in heat.
90. What is thermal pollution?
Answer: Increase in water temperature by industries → harms aquatic life.
91. What is geothermal gradient?
Answer: Increase in Earth’s temperature with depth.
92. Why does water have maximum density at 4°C?
Answer: Molecular arrangement becomes most compact.
93. Why does water expand below 4°C?
Answer: Due to hydrogen bonding.
94. Why icebergs float even though they are huge?
Answer: Ice density < water density.
95. What is thermodynamic system?
Answer: Part of universe selected for study.
96. Types of thermodynamic systems?
Answer:
Open (mass & energy exchange)
Closed (only energy exchange)
Isolated (no exchange)
97. What is efficiency of heat engine?
Answer: η = (Work output / Heat input)
98. Why can no engine be 100% efficient?
Answer: Due to second law; some heat is always lost to surroundings.
99. What is a heat pump?
Answer: Device that transfers heat from cold region to hot region.
100. What is enthalpy?
Answer: Total heat content of a system.