Q.1 Which mode of heat transfer does not require a medium?
Conduction
Convection
Radiation
Evaporation
Explanation - Radiation can occur through a vacuum as it involves electromagnetic waves, unlike conduction or convection which require a medium.
Correct answer is: Radiation
Q.2 The SI unit of thermal conductivity is:
W/m
W/m·K
J/K
W/K
Explanation - Thermal conductivity is measured in watts per meter per Kelvin (W/m·K).
Correct answer is: W/m·K
Q.3 A metal rod is heated at one end. Heat transfer through the rod occurs by:
Conduction
Convection
Radiation
Evaporation
Explanation - Conduction is the transfer of heat through direct molecular collisions in solids.
Correct answer is: Conduction
Q.4 In calorimetry, the principle used is:
Heat is absorbed but not released
Heat gained equals heat lost
Mass of water remains constant
Temperature remains constant
Explanation - Calorimetry is based on the conservation of energy where heat lost by one body equals heat gained by another.
Correct answer is: Heat gained equals heat lost
Q.5 Which of the following materials is the best conductor of heat?
Iron
Aluminium
Copper
Wood
Explanation - Copper has very high thermal conductivity compared to iron, aluminum, and wood.
Correct answer is: Copper
Q.6 The process of heat transfer in liquids and gases by actual motion of molecules is called:
Conduction
Radiation
Convection
Reflection
Explanation - Convection occurs due to the bulk movement of molecules in fluids.
Correct answer is: Convection
Q.7 The emissivity of a perfect black body is:
0
0.5
1
Varies with temperature
Explanation - A perfect black body has an emissivity of 1, meaning it absorbs all incident radiation.
Correct answer is: 1
Q.8 The device used to measure the specific heat capacity of a substance is called:
Thermometer
Barometer
Calorimeter
Manometer
Explanation - A calorimeter is specifically designed to measure the heat exchange between substances.
Correct answer is: Calorimeter
Q.9 In a perfectly insulated system, the net heat exchange is:
Zero
Maximum
Infinite
Depends on initial temperatures
Explanation - A perfectly insulated system is adiabatic, meaning no heat is exchanged with the surroundings.
Correct answer is: Zero
Q.10 The heat required to raise the temperature of 1 kg of a substance by 1°C is called:
Latent heat
Specific heat capacity
Thermal conductivity
Heat capacity
Explanation - Specific heat capacity is the amount of heat required to raise the temperature of 1 kg of a substance by 1°C.
Correct answer is: Specific heat capacity
Q.11 Which of the following surfaces is the best absorber of heat radiation?
Polished silver
White rough surface
Black rough surface
Smooth gold
Explanation - A black rough surface absorbs heat radiation most efficiently due to higher emissivity.
Correct answer is: Black rough surface
Q.12 The Stefan-Boltzmann law relates to:
Conduction
Convection
Black body radiation
Specific heat
Explanation - Stefan-Boltzmann law gives the total energy radiated per unit surface area of a black body.
Correct answer is: Black body radiation
Q.13 The thermal conductivity of gases compared to solids is:
Higher
Lower
Equal
Variable
Explanation - Gases generally have lower thermal conductivity because their molecules are far apart, leading to less effective transfer of heat.
Correct answer is: Lower
Q.14 Latent heat is the heat energy:
Used to change temperature
Released when cooling occurs
Used to change the state of a substance
Lost during conduction
Explanation - Latent heat is absorbed or released during a phase change without temperature change.
Correct answer is: Used to change the state of a substance
Q.15 The unit of heat is:
Joule
Kelvin
Watt
Coulomb
Explanation - Heat is a form of energy, and its SI unit is Joule.
Correct answer is: Joule
Q.16 In conduction, the heat flows:
From cold to hot region
From hot to cold region
Equally in both directions
Depends on material
Explanation - Heat always flows from a higher temperature region to a lower temperature region.
Correct answer is: From hot to cold region
Q.17 The calorific value of a fuel is measured in:
Joule
Watt
J/kg
Kelvin
Explanation - Calorific value represents the energy released per kilogram of fuel burned, measured in Joules per kilogram.
Correct answer is: J/kg
Q.18 Which color is a poor emitter of heat radiation?
Black
White
Blue
Green
Explanation - White and shiny surfaces are poor emitters of heat radiation compared to black surfaces.
Correct answer is: White
Q.19 When ice melts to water, the heat absorbed is called:
Latent heat of vaporization
Latent heat of fusion
Specific heat
Sensible heat
Explanation - Latent heat of fusion is the heat required to convert a solid to liquid without a temperature change.
Correct answer is: Latent heat of fusion
Q.20 Which of the following is not a mode of heat transfer?
Conduction
Convection
Radiation
Compression
Explanation - Compression is not a mode of heat transfer, it is a mechanical process.
Correct answer is: Compression
Q.21 The thermal expansion of solids is primarily due to:
Decrease in molecular motion
Increase in molecular vibration
Change in density
External pressure
Explanation - As temperature increases, molecules vibrate more, causing expansion in solids.
Correct answer is: Increase in molecular vibration
Q.22 The heat transfer rate by conduction depends on:
Material and temperature difference
Shape only
Pressure only
Color of surface
Explanation - Conduction depends on the thermal conductivity of the material and the temperature gradient.
Correct answer is: Material and temperature difference
Q.23 The amount of heat required to change a unit mass of a substance from liquid to gas is called:
Latent heat of vaporization
Latent heat of fusion
Specific heat
Heat capacity
Explanation - Latent heat of vaporization is the heat needed to convert a liquid into gas without changing temperature.
Correct answer is: Latent heat of vaporization
Q.24 A perfectly reflecting surface has an emissivity of:
0
0.5
1
2
Explanation - A perfectly reflecting surface does not absorb any radiation, so its emissivity is 0.
Correct answer is: 0
Q.25 The thermal resistance of a wall increases when:
Thermal conductivity increases
Thickness decreases
Thickness increases
Surface area increases
Explanation - Thermal resistance is directly proportional to the thickness of the wall and inversely proportional to thermal conductivity and area.
Correct answer is: Thickness increases