1. Heat is a form of —
A) Light energy
B) Kinetic energy
C) Potential energy
D) Electrical energy
Answer: B) Kinetic energy
Explanation: Heat is the total kinetic energy of all molecules of a substance due to their random motion.
2. The S.I. unit of heat is —
A) Calorie
B) Joule
C) Kelvin
D) Erg
Answer: B) Joule
Explanation: Joule (J) is the SI unit of heat and energy. 1 calorie = 4.186 J.
3. The device used to measure temperature is —
A) Barometer
B) Thermometer
C) Hygrometer
D) Pyrometer
Answer: B) Thermometer
Explanation: Thermometers are used to measure temperature.
4. The S.I. unit of temperature is —
A) Celsius
B) Fahrenheit
C) Kelvin
D) Centigrade
Answer: C) Kelvin
Explanation: Kelvin (K) is the SI unit of thermodynamic temperature.
5. The normal temperature of the human body is —
A) 98.4°F
B) 96.8°F
C) 100°F
D) 99°F
Answer: A) 98.4°F
Explanation: Normal body temperature is 37°C or 98.4°F.
6. The temperature at which a solid changes into liquid is called —
A) Boiling point
B) Melting point
C) Evaporation point
D) Condensation point
Answer: B) Melting point
Explanation: Melting point is the temperature at which solid becomes liquid.
7. The temperature at which liquid changes into gas is called —
A) Melting point
B) Freezing point
C) Boiling point
D) Evaporation point
Answer: C) Boiling point
Explanation: Boiling point is the temperature at which vaporization occurs.
8. The freezing point of water is —
A) 0°C
B) 32°C
C) 100°C
D) 273 K
Answer: A) 0°C
Explanation: Water freezes at 0°C or 273 K.
9. The boiling point of water is —
A) 50°C
B) 90°C
C) 100°C
D) 120°C
Answer: C) 100°C
Explanation: At normal pressure, water boils at 100°C or 373 K.
10. The heat required to raise the temperature of 1 kg of a substance by 1°C is called —
A) Latent heat
B) Specific heat
C) Heat capacity
D) Thermal energy
Answer: B) Specific heat
Explanation: Specific heat (c) = Heat / (mass × temperature change).
11. The S.I. unit of specific heat is —
A) J/kg
B) J/kg°C
C) J/°C
D) J/m²
Answer: B) J/kg°C
Explanation: Unit = joules per kilogram per degree Celsius.
12. The heat required to change the state of a substance without change in temperature is called —
A) Latent heat
B) Sensible heat
C) Specific heat
D) Potential energy
Answer: A) Latent heat
Explanation: Latent heat changes state but not temperature.
13. The S.I. unit of latent heat is —
A) J/kg
B) J/mol
C) Cal/g
D) KJ/kg
Answer: A) J/kg
Explanation: It is measured as energy per unit mass.
14. Heat always flows from —
A) Cold to hot
B) Hot to cold
C) Lower to higher potential
D) None
Answer: B) Hot to cold
Explanation: Heat naturally flows from higher temperature to lower temperature.
15. The process by which heat is transferred without actual movement of particles is —
A) Conduction
B) Convection
C) Radiation
D) Evaporation
Answer: C) Radiation
Explanation: In radiation, heat travels through vacuum by electromagnetic waves.
16. Conduction takes place mainly in —
A) Solids
B) Liquids
C) Gases
D) Vacuum
Answer: A) Solids
Explanation: Solids conduct heat because their particles are closely packed.
17. Convection takes place mainly in —
A) Solids
B) Liquids and gases
C) Metals
D) Vacuum
Answer: B) Liquids and gases
Explanation: Convection is due to movement of particles, which occurs in fluids.
18. Heat transfer by radiation requires —
A) Medium
B) Air
C) Solid contact
D) No medium
Answer: D) No medium
Explanation: Radiation can occur even in vacuum, e.g., heat from the Sun.
19. A good conductor of heat is —
A) Copper
B) Wood
C) Plastic
D) Rubber
Answer: A) Copper
Explanation: Metals like copper and aluminum are good conductors.
20. A bad conductor of heat is —
A) Iron
B) Aluminum
C) Glass
D) Silver
Answer: C) Glass
Explanation: Glass is a poor conductor and used in thermos flasks to prevent heat loss.
21. The best conductor of heat among the following is —
A) Copper
B) Silver
C) Iron
D) Aluminium
Answer: B) Silver
Explanation: Silver is the best conductor of heat and electricity among metals.
22. The poorest conductor of heat among the following is —
A) Rubber
B) Water
C) Air
D) Wood
Answer: C) Air
Explanation: Air has very low thermal conductivity and acts as an insulator.
23. The process by which heat is transferred in solids is —
A) Conduction
B) Convection
C) Radiation
D) Diffusion
Answer: A) Conduction
Explanation: In solids, heat is transferred through molecular vibrations.
24. The process by which heat is transferred in liquids and gases is —
A) Conduction
B) Convection
C) Radiation
D) Diffusion
Answer: B) Convection
Explanation: Heat transfer occurs through actual movement of fluid molecules.
25. The process by which heat is transferred from the Sun to the Earth is —
A) Conduction
B) Convection
C) Radiation
D) Reflection
Answer: C) Radiation
Explanation: Radiation can travel through vacuum — no medium required.
26. Which of the following surfaces is a good absorber of heat?
A) Shiny and white
B) Smooth and silver
C) Rough and black
D) Polished and bright
Answer: C) Rough and black
Explanation: Dark, rough surfaces absorb more heat radiation.
27. A good absorber of heat is also a good —
A) Reflector
B) Radiator (emitter)
C) Conductor
D) Insulator
Answer: B) Radiator (emitter)
Explanation: According to Kirchhoff’s law, good absorbers are good emitters.
28. In a thermos flask, heat transfer is minimized by —
A) Conduction only
B) Convection only
C) Radiation only
D) All three methods
Answer: D) All three methods
Explanation: Thermos prevents heat loss by conduction, convection, and radiation.
29. The fixed points of a thermometer are —
A) Freezing and boiling points of water
B) Room and body temperature
C) Boiling point and melting point of mercury
D) Ice point and steam point
Answer: A) Freezing and boiling points of water
Explanation: These two fixed points are used to calibrate thermometers.
30. Temperature is a measure of —
A) Total heat energy
B) Average kinetic energy of particles
C) Potential energy
D) Internal energy
Answer: B) Average kinetic energy of particles
Explanation: Temperature measures how fast particles move on average.
31. Which of the following has the highest specific heat?
A) Water
B) Mercury
C) Iron
D) Copper
Answer: A) Water
Explanation: Water has very high specific heat (4200 J/kg°C), making it an excellent coolant.
32. A device used to measure high temperatures (e.g., in furnaces) is —
A) Clinical thermometer
B) Laboratory thermometer
C) Pyrometer
D) Manometer
Answer: C) Pyrometer
Explanation: Pyrometers measure very high temperatures without contact.
33. The specific heat of a substance depends on —
A) Nature of material
B) Shape of material
C) Color of material
D) Size of material
Answer: A) Nature of material
Explanation: Different materials store heat energy differently due to molecular structure.
34. The amount of heat required to change 1 kg of ice into water at 0°C without change of temperature is called —
A) Latent heat of vaporization
B) Latent heat of fusion
C) Specific heat
D) Thermal capacity
Answer: B) Latent heat of fusion
Explanation: It’s the heat needed to melt solid → liquid at constant temperature.
35. The amount of heat required to change 1 kg of water into vapor at 100°C without temperature change is —
A) Latent heat of fusion
B) Latent heat of vaporization
C) Specific heat
D) Melting heat
Answer: B) Latent heat of vaporization
Explanation: It’s the energy needed for phase change from liquid to vapor.
36. The S.I. unit of heat capacity is —
A) Joule
B) J/kg°C
C) J/°C
D) Calorie
Answer: C) J/°C
Explanation: Heat capacity = Heat / Temperature change → joules per degree.
37. When ice melts into water, heat energy —
A) Increases temperature
B) Decreases temperature
C) Changes state only
D) Is lost completely
Answer: C) Changes state only
Explanation: During melting, temperature remains constant — heat used for state change.
38. When water boils, the temperature —
A) Increases continuously
B) Decreases gradually
C) Remains constant
D) Becomes zero
Answer: C) Remains constant
Explanation: During boiling, heat is used to convert liquid → vapor (latent heat).
39. Expansion of a substance on heating is due to —
A) Decrease in molecular distance
B) Increase in molecular distance
C) Chemical reaction
D) Change in density
Answer: B) Increase in molecular distance
Explanation: On heating, molecules vibrate more and move farther apart.
40. The increase in length of a solid when heated is called —
A) Cubical expansion
B) Linear expansion
C) Superficial expansion
D) Thermal expansion
Answer: B) Linear expansion
Explanation: Linear expansion occurs along one dimension (length).
41. When a metal ring is heated, the hole in the ring —
A) Expands
B) Contracts
C) Remains same
D) Becomes irregular
Answer: A) Expands
Explanation: On heating, every part of the ring expands; hence, even the hole increases in size.
42. The coefficient of linear expansion is expressed in —
A) °C
B) m
C) m/°C
D) per °C
Answer: D) per °C
Explanation: Coefficient of expansion = fractional change in length per °C rise in temperature.
43. The expansion of a liquid on heating is called —
A) Linear expansion
B) Cubical expansion
C) Superficial expansion
D) Thermal expansion
Answer: B) Cubical expansion
Explanation: Liquids have volume expansion because they have no fixed shape.
44. The temperature at which water has maximum density is —
A) 0°C
B) 4°C
C) 10°C
D) 100°C
Answer: B) 4°C
Explanation: Water is densest at 4°C; below or above this, density decreases.
45. The process of heat transfer in which no medium is required is —
A) Conduction
B) Convection
C) Radiation
D) None of these
Answer: C) Radiation
Explanation: Radiation can occur even through vacuum (e.g., sunlight).
46. The heat energy required to convert 1 g of ice at 0°C to 1 g of water at 0°C is —
A) 80 cal
B) 540 cal
C) 100 cal
D) 1 cal
Answer: A) 80 cal
Explanation: Latent heat of fusion of ice = 80 cal/g.
47. The heat energy required to convert 1 g of water at 100°C into steam at 100°C is —
A) 80 cal
B) 540 cal
C) 100 cal
D) 1 cal
Answer: B) 540 cal
Explanation: Latent heat of vaporization of water = 540 cal/g.
48. When a solid is heated, its mass —
A) Increases
B) Decreases
C) Remains constant
D) First increases then decreases
Answer: C) Remains constant
Explanation: Heating changes size and volume but not mass.
49. When heat is supplied to a body, it may —
A) Raise temperature only
B) Change state only
C) Either raise temperature or change state
D) Reflect energy
Answer: C) Either raise temperature or change state
Explanation: Depending on the condition, heat causes temperature rise or phase change.
50. The transfer of heat by convection in a liquid takes place due to —
A) Conduction of molecules
B) Radiation of molecules
C) Movement of molecules
D) Collision of molecules
Answer: C) Movement of molecules
Explanation: In convection, molecules move carrying heat energy.
51. When water is heated from 0°C to 4°C, its volume —
A) Increases
B) Decreases
C) Remains constant
D) Increases then decreases
Answer: B) Decreases
Explanation: Water shows anomalous expansion — contracts till 4°C and then expands.
52. The anomalous expansion of water is useful in —
A) Boiling water faster
B) Survival of aquatic life in winter
C) Increasing density of water
D) Freezing quickly
Answer: B) Survival of aquatic life in winter
Explanation: Ice floats and insulates lower water layers, allowing aquatic life to survive.
53. The heat energy per unit mass required to change a solid into a liquid without temperature change is —
A) Latent heat of vaporization
B) Latent heat of fusion
C) Specific heat
D) Thermal capacity
Answer: B) Latent heat of fusion
Explanation: Fusion is solid → liquid phase change.
54. The heat energy per unit mass required to change a liquid into vapor without temperature change is —
A) Latent heat of fusion
B) Latent heat of vaporization
C) Specific heat
D) Thermal capacity
Answer: B) Latent heat of vaporization
Explanation: It measures heat required for liquid → vapor.
55. The process of cooling due to evaporation takes place because —
A) All molecules escape
B) The faster molecules leave, reducing average kinetic energy
C) Molecules gain energy from surroundings
D) Temperature increases
Answer: B) The faster molecules leave, reducing average kinetic energy
Explanation: Evaporation removes high-energy molecules → cooling effect.
56. When you feel cool after applying alcohol on skin, it is due to —
A) Boiling
B) Radiation
C) Evaporation
D) Condensation
Answer: C) Evaporation
Explanation: Alcohol evaporates quickly, taking away heat from the skin.
57. The boiling point of water decreases when —
A) Pressure increases
B) Pressure decreases
C) Temperature increases
D) Impurities increase
Answer: B) Pressure decreases
Explanation: At higher altitudes (low pressure), water boils at lower temperatures.
58. When vapor changes into liquid, the process is called —
A) Fusion
B) Condensation
C) Evaporation
D) Boiling
Answer: B) Condensation
Explanation: Conversion of gas to liquid by releasing heat energy.
59. The boiling point of water increases when —
A) Pressure increases
B) Pressure decreases
C) Temperature decreases
D) Air is removed
Answer: A) Pressure increases
Explanation: More pressure means molecules need higher energy to escape.
60. The process of heat transfer that takes place between Earth and Sun is —
A) Conduction
B) Convection
C) Radiation
D) Reflection
Answer: C) Radiation
Explanation: Heat from the Sun reaches Earth through vacuum via radiation.
61. The transfer of heat by molecular collision is called —
A) Conduction
B) Convection
C) Radiation
D) Reflection
Answer: A) Conduction
Explanation: In conduction, energy is passed from one molecule to another by vibration and collision.
62. The metallic rod feels colder than a wooden rod at the same temperature because —
A) Metal expands more
B) Metal conducts heat faster
C) Metal is heavier
D) Wood absorbs moisture
Answer: B) Metal conducts heat faster
Explanation: Metal quickly draws heat away from the hand due to high thermal conductivity.
63. Heat energy absorbed or released during change of state is called —
A) Sensible heat
B) Latent heat
C) Specific heat
D) Thermal energy
Answer: B) Latent heat
Explanation: Latent heat changes phase without temperature change.
64. The phenomenon of sea breeze is due to —
A) Conduction
B) Convection
C) Radiation
D) Reflection
Answer: B) Convection
Explanation: During day, warm air rises from land and cool air from sea replaces it — convection current.
65. The phenomenon of land breeze occurs —
A) During the day
B) During the night
C) During evening only
D) In deserts only
Answer: B) During the night
Explanation: At night, land cools faster than sea — air moves from land to sea.
66. The process by which heat is transferred in liquids and gases due to actual movement of particles is —
A) Conduction
B) Convection
C) Radiation
D) Reflection
Answer: B) Convection
Explanation: Fluids transfer heat by movement of warmer and cooler parts.
67. The device which minimizes heat loss due to conduction, convection, and radiation is —
A) Radiator
B) Thermos flask
C) Refrigerator
D) Solar cooker
Answer: B) Thermos flask
Explanation: Vacuum and reflective walls prevent all three modes of heat transfer.
68. On a hot day, a person wearing white clothes feels cooler because —
A) White color absorbs all heat
B) White color reflects most of the heat
C) White color emits heat
D) White color absorbs sunlight
Answer: B) White color reflects most of the heat
Explanation: Light-colored clothes reflect heat and keep the body cool.
69. The heat required to raise the temperature of a body by 1°C is called —
A) Specific heat
B) Latent heat
C) Thermal capacity
D) Heat energy
Answer: C) Thermal capacity
Explanation: Thermal capacity = Heat required / temperature change = m × c.
70. When ice at 0°C melts to water at 0°C, heat absorbed is —
A) Latent heat
B) Specific heat
C) Sensible heat
D) Conduction heat
Answer: A) Latent heat
Explanation: Heat changes phase (solid → liquid) without temperature rise.
71. When vapor converts into liquid, it —
A) Absorbs heat
B) Releases heat
C) Does not change energy
D) Cools rapidly
Answer: B) Releases heat
Explanation: Condensation releases latent heat to surroundings.
72. Frost forms on cold surfaces due to —
A) Evaporation
B) Sublimation
C) Condensation
D) Freezing
Answer: B) Sublimation
Explanation: Water vapor directly changes to ice without becoming liquid.
73. Boiling occurs when —
A) Temperature decreases
B) Vapour pressure equals external pressure
C) Vapour pressure becomes less than atmospheric pressure
D) Vapour pressure becomes zero
Answer: B) Vapour pressure equals external pressure
Explanation: Boiling begins when internal vapor pressure matches external pressure.
74. Evaporation of water is faster when —
A) Temperature is low
B) Air is still
C) Humidity is low
D) Surface area is small
Answer: C) Humidity is low
Explanation: Dry air allows faster evaporation since it can hold more vapor.
75. Which of the following factors does not affect evaporation?
A) Surface area
B) Temperature
C) Humidity
D) Density of liquid
Answer: D) Density of liquid
Explanation: Evaporation depends mainly on surface area, temperature, and humidity.
76. The freezing point of water in Kelvin scale is —
A) 100 K
B) 273 K
C) 373 K
D) 273°C
Answer: B) 273 K
Explanation: 0°C=273 K0°C = 273 \, K0°C=273K
77. The boiling point of water in Kelvin scale is —
A) 273 K
B) 300 K
C) 373 K
D) 400 K
Answer: C) 373 K
Explanation: 100°C=373 K100°C = 373 \, K100°C=373K
78. Which law states that heat lost by hot body equals heat gained by cold body in an isolated system?
A) Joule’s Law
B) Law of Cooling
C) Principle of Calorimetry
D) Newton’s Law
Answer: C) Principle of Calorimetry
Explanation: Qlost=QgainedQ_{\text{lost}} = Q_{\text{gained}}Qlost=Qgained — conservation of energy.
79. The instrument used to measure specific heat capacity is —
A) Thermometer
B) Calorimeter
C) Manometer
D) Hygrometer
Answer: B) Calorimeter
Explanation: Calorimeter measures heat exchange between substances.
80. The process in which heat is transferred from one part of a body to another without movement of particles is —
A) Convection
B) Conduction
C) Radiation
D) Reflection
Answer: B) Conduction
Explanation: In solids, heat passes by vibration of particles without actual movement.
81. When a body cools, it —
A) Gains heat
B) Loses heat
C) Maintains temperature
D) Expands
Answer: B) Loses heat
Explanation: Cooling occurs due to loss of internal energy or heat to surroundings.
82. A liquid thermometer works on the principle of —
A) Thermal expansion
B) Convection
C) Conduction
D) Radiation
Answer: A) Thermal expansion
Explanation: Liquids like mercury expand when heated, and the expansion indicates temperature.
83. In thermodynamics, the measure of disorder or randomness is called —
A) Energy
B) Entropy
C) Pressure
D) Heat
Answer: B) Entropy
Explanation: Entropy measures the degree of disorder in a system.
84. The heat required to raise the temperature of 1 g of water by 1°C is —
A) 1 cal
B) 4.2 cal
C) 10 cal
D) 0.1 cal
Answer: A) 1 cal
Explanation: By definition, 1 calorie = heat needed to raise 1 g of water by 1°C.
85. The specific heat capacity of water is —
A) 420 J/kg°C
B) 4200 J/kg°C
C) 100 J/kg°C
D) 4.2 J/kg°C
Answer: B) 4200 J/kg°C
Explanation: Water has a high specific heat of 4200 J/kg°C, making it an effective coolant.
86. A black body is a —
A) Perfect absorber and perfect emitter of heat
B) Perfect reflector
C) Perfect insulator
D) Partial absorber
Answer: A) Perfect absorber and perfect emitter of heat
Explanation: A black body absorbs all incident radiation and emits maximum possible energy.
87. Which of the following surfaces is the best emitter of heat?
A) Polished white surface
B) Rough black surface
C) Smooth silver surface
D) Mirror surface
Answer: B) Rough black surface
Explanation: Black, rough surfaces are best absorbers and emitters of radiation.
88. The unit of heat energy commonly used in food energy is —
A) Calorie
B) Joule
C) Kilocalorie
D) Kelvin
Answer: C) Kilocalorie
Explanation: 1 kilocalorie = 1000 calories; used to measure energy in food.
89. Which of the following has the lowest thermal conductivity?
A) Iron
B) Wood
C) Silver
D) Aluminium
Answer: B) Wood
Explanation: Wood is an insulator and does not allow easy transfer of heat.
90. Which gas is a poor conductor of heat and is used in thermos flasks?
A) Oxygen
B) Nitrogen
C) Hydrogen
D) Carbon dioxide
Answer: B) Nitrogen
Explanation: Nitrogen is used because it has low thermal conductivity and prevents oxidation.
91. The relationship between heat (Q), mass (m), specific heat (c), and temperature difference (ΔT) is —
A) Q = mc/ΔT
B) Q = m + c + ΔT
C) Q = mcΔT
D) Q = m/cΔT
Answer: C) Q = mcΔT
Explanation: Formula for heat exchange when temperature changes.
92. Which of the following is a temperature scale with absolute zero?
A) Celsius
B) Fahrenheit
C) Kelvin
D) Centigrade
Answer: C) Kelvin
Explanation: Absolute zero (0 K) is the temperature at which molecular motion stops.
93. Absolute zero temperature is —
A) 0°C
B) −100°C
C) −273°C
D) −373°C
Answer: C) −273°C
Explanation: −273.15°C = 0 K, the lowest possible temperature.
94. The material used for making electrical heating elements is —
A) Copper
B) Aluminium
C) Nichrome
D) Iron
Answer: C) Nichrome
Explanation: Nichrome has high resistivity and withstands high temperature, making it ideal for heaters.
95. Which law states that “the rate of heat loss of a body is directly proportional to the difference in temperature between the body and its surroundings”?
A) Stefan’s Law
B) Newton’s Law of Cooling
C) Wien’s Law
D) Kirchhoff’s Law
Answer: B) Newton’s Law of Cooling
Explanation: It applies to bodies cooling by radiation or convection.
96. When water is boiled, bubbles appear because —
A) Air dissolved in water escapes
B) Water starts evaporating
C) Vapor pressure increases
D) All the above
Answer: D) All the above
Explanation: Boiling causes vapor formation and air release due to heat energy.
97. The freezing point of seawater is —
A) 0°C
B) −2°C
C) 5°C
D) −10°C
Answer: B) −2°C
Explanation: Due to dissolved salts, seawater freezes below 0°C.
98. The process of changing directly from solid to gas is called —
A) Melting
B) Sublimation
C) Evaporation
D) Condensation
Answer: B) Sublimation
Explanation: Examples include camphor and dry ice, which sublimate directly.
99. When ice melts into water, energy —
A) Is absorbed
B) Is released
C) Remains constant
D) Becomes kinetic
Answer: A) Is absorbed
Explanation: Heat is absorbed (latent heat of fusion) to overcome molecular bonds.
100. Which of the following is used in refrigerators as a cooling agent?
A) Oxygen
B) Ammonia
C) Carbon dioxide
D) Nitrogen
Answer: B) Ammonia
Explanation: Ammonia is commonly used as a refrigerant due to its high latent heat of vaporization.