Heat and Temperature MCQs 61 to 90 Questions with details Answers.

Heat and Temperature MCQs 61 to 90

61. What is the main reason for the formation of dew?

A. Evaporation of water from surfaces. B. Condensation of water vapor on cool surfaces. C. Freezing of rainwater. D. Sublimation of ice.

Correct Answer: B

Explanation: Dew forms when the air cools down to its dew point, causing water vapor in the air to condense into liquid droplets on surfaces that are cooler than the air.

62. Why does sweating cool down the body?

A. Evaporation of sweat absorbs latent heat from the body. B. Sweat is naturally cold. C. Sweat creates a barrier against heat. D. Sweat reflects sunlight.

Correct Answer: A

Explanation: When sweat evaporates from the skin, it absorbs a significant amount of latent heat of vaporization from the body, leading to a cooling effect.

63. Which of the following is an example of heat transfer by convection?

A. A metal spoon getting hot in soup. B. Sunlight warming your face. C. Hot air rising from a heater. D. Heat flowing through a window pane.

Correct Answer: C

Explanation: Convection involves the movement of fluid (liquid or gas) itself. Hot air rising from a heater is a classic example of a convection current.

64. What happens to the internal energy of a gas when it is compressed rapidly (adiabatically)?

A. It decreases. B. It remains constant. C. It converts to potential energy. D. It increases.

Correct Answer: D

Explanation: When a gas is compressed rapidly, work is done *on* the gas. If this happens quickly enough that no heat can escape (adiabatically), the work done increases the internal energy of the gas, leading to a rise in temperature.

65. Why are cooking utensils often made with wooden or plastic handles?

A. Wood and plastic are poor conductors of heat. B. Wood and plastic are cheaper. C. Wood and plastic are good conductors of heat. D. Wood and plastic are more durable.

Correct Answer: A

Explanation: Wood and plastic are insulators (poor conductors of heat). This prevents heat from the hot cooking pan from transferring quickly to your hand, making the handles safe to touch.

66. What is the unit of heat energy in the SI system?

A. Calorie. B. Joule. C. Celsius. D. Watt.

Correct Answer: B

Explanation: The Joule (J) is the SI unit for all forms of energy, including heat energy.

67. What is the relationship between 1 calorie and Joules?

A. 1 cal ≈ 4.184 J. B. 1 cal ≈ 0.24 J. C. 1 cal = 1 J. D. 1 cal = 1000 J.

Correct Answer: A

Explanation: The conversion factor between calories and Joules is approximately 1 calorie = 4.184 Joules.

68. Why do solids have a definite shape and volume?

A. Their particles have high kinetic energy. B. Their particles are far apart. C. Their particles are held in fixed positions by strong forces. D. They are incompressible.

Correct Answer: C

Explanation: In solids, the constituent particles (atoms, molecules, or ions) are tightly bound by strong intermolecular forces and vibrate about fixed positions, giving solids a rigid structure.

69. What happens to the boiling point of water at high altitudes?

A. It decreases. B. It increases. C. It remains the same. D. It becomes undefined.

Correct Answer: A

Explanation: At higher altitudes, atmospheric pressure is lower. Since boiling occurs when vapor pressure equals external pressure, water boils at a lower temperature at high altitudes.

70. Which of the following is NOT a good thermal insulator?

A. Air. B. Wood. C. Silver. D. Styrofoam.

Correct Answer: C

Explanation: Silver is an excellent conductor of heat, meaning it allows heat to pass through it easily, unlike air, wood, and styrofoam which are good insulators.

71. What is the main principle behind a pressure cooker?

A. Decreasing the boiling point of water. B. Increasing the specific heat capacity of water. C. Trapping latent heat. D. Increasing the boiling point of water by increasing pressure.

Correct Answer: D

Explanation: A pressure cooker works by trapping steam, which increases the pressure inside. This elevated pressure raises the boiling point of water, allowing food to cook at a higher temperature and thus faster.

72. What is the primary mode of heat transfer from the Sun to the Earth?

A. Radiation. B. Conduction. C. Convection. D. Absorption.

Correct Answer: A

Explanation: The vast emptiness of space between the Sun and Earth means heat cannot be transferred by conduction or convection. Instead, it travels as electromagnetic waves (radiation).

73. Why does ice float on water?

A. Ice is colder than water. B. Ice is less dense than water. C. Water has a higher surface tension. D. Ice has a lower specific heat capacity.

Correct Answer: B

Explanation: Unlike most substances, water expands when it freezes, meaning ice is less dense than liquid water at 0°C. This lower density allows ice to float.

74. What is the specific heat capacity of a substance a measure of?

A. How much energy is required to raise its temperature. B. Its ability to conduct heat. C. Its melting point. D. Its thermal expansion coefficient.

Correct Answer: A

Explanation: Specific heat capacity quantifies the amount of heat energy required to raise the temperature of a unit mass of a substance by one degree Celsius (or Kelvin).

75. Why do puddles dry up faster on a windy day?

A. Wind increases the water's temperature. B. Wind adds heat to the water. C. Wind carries away saturated air, promoting more evaporation. D. Wind causes the water to freeze.

Correct Answer: C

Explanation: Wind removes the water vapor that has evaporated from the puddle, preventing the air above the puddle from becoming saturated. This allows more water molecules to escape into the air, increasing the rate of evaporation.

76. What is the main function of a radiator in a car engine?

A. To add heat to the engine. B. To increase the engine's temperature. C. To transfer excess heat from the engine to the surroundings. D. To convert heat into mechanical energy.

Correct Answer: C

Explanation: The radiator is part of the car's cooling system. It dissipates the heat generated by the engine into the atmosphere, preventing the engine from overheating.

77. Which of the following is an example of latent heat being released?

A. Ice melting into water. B. Steam condensing into water. C. Water heating up from 20°C to 50°C. D. A solid sublimating into a gas.

Correct Answer: B

Explanation: Latent heat is released during phase changes from a higher energy state to a lower energy state. Condensation (gas to liquid) releases latent heat, which is why steam burns are more severe than boiling water burns at the same temperature.

78. What is the freezing point of water on the Fahrenheit scale?

A. 32 °F. B. 0 °F. C. 212 °F. D. 98 °F.

Correct Answer: A

Explanation: The freezing point of water is 0 °C, which corresponds to 32 °F on the Fahrenheit scale.

79. Why do bridges have expansion joints?

A. To make them lighter. B. To allow for water drainage. C. To prevent rusting. D. To accommodate thermal expansion and contraction.

Correct Answer: D

Explanation: Materials expand when heated and contract when cooled. Expansion joints are built into bridges to allow for these changes in length due to temperature fluctuations, preventing structural damage.

80. What is the process of heat transfer that involves direct contact between particles?

A. Convection. B. Conduction. C. Radiation. D. Evaporation.

Correct Answer: B

Explanation: Conduction is the transfer of heat through direct contact, where vibrating particles transfer kinetic energy to adjacent particles without any net movement of the material itself.

81. Which of the following best describes the molecular motion in a gas?

A. Random, rapid, and widely spaced. B. Vibrating in fixed positions. C. Sliding past each other. D. Oscillating back and forth.

Correct Answer: A

Explanation: Gas particles have very high kinetic energy, move randomly and rapidly, and are widely spaced with negligible intermolecular forces, allowing them to fill any container.

82. What is the term for the amount of heat required to change 1 kg of a substance from solid to liquid at its melting point?

A. Specific heat capacity. B. Heat of fusion. C. Latent heat of fusion. D. Thermal conductivity.

Correct Answer: C

Explanation: The latent heat of fusion is the specific amount of heat energy absorbed by a substance to change from a solid to a liquid state at its melting point without a change in temperature.

83. Why does a black car get hotter than a white car on a sunny day?

A. Black surfaces conduct heat better. B. Black surfaces absorb more radiant heat. C. White surfaces emit more heat. D. White surfaces have lower specific heat.

Correct Answer: B

Explanation: Dark-colored surfaces are good absorbers of thermal radiation (like sunlight), converting more of it into heat, while light-colored surfaces reflect more radiation.

84. What is the primary method of heat transfer in a vacuum?

A. Conduction. B. Convection. C. Evaporation. D. Radiation.

Correct Answer: D

Explanation: Radiation is the only method of heat transfer that does not require a medium, making it the primary way heat travels through a vacuum, such as space.

85. What property of a substance determines how much its temperature changes when a given amount of heat is added?

A. Specific heat capacity. B. Density. C. Thermal conductivity. D. Latent heat.

Correct Answer: A

Explanation: Specific heat capacity is a measure of a substance's resistance to temperature change. A substance with a high specific heat capacity requires more heat to raise its temperature by a certain amount.

86. Why does a cold drink bottle taken out of the refrigerator show water droplets on its outer surface?

A. The bottle is leaking. B. The coldness from the bottle is attracting water. C. Water vapor in the air condenses on the cold surface. D. The bottle is absorbing water from the air.

Correct Answer: C

Explanation: The cold surface of the bottle cools the surrounding air to below its dew point. This causes the invisible water vapor in the air to condense into visible liquid water droplets on the bottle's surface.

87. What is the effect of adding salt to water on its freezing point?

A. Freezing point increases. B. Freezing point remains constant. C. Freezing point decreases. D. Freezing point first increases then decreases.

Correct Answer: C

Explanation: Adding impurities (like salt) to a liquid lowers its freezing point. This is why salt is used on roads in winter to prevent ice formation.

88. Which of the following is an example of heat transfer by conduction in everyday life?

A. Heating a pan on a stove. B. A hot air balloon rising. C. Feeling the warmth of a campfire. D. Water boiling in a kettle.

Correct Answer: A

Explanation: When a pan is placed on a hot stove, heat is transferred directly from the stove burner to the pan through conduction, and then through the pan material to the food.

89. What is the primary mechanism of heat transfer through a double-paned window?

A. Increased conduction. B. Enhanced radiation. C. Reduced conduction and convection by trapped air/gas. D. Increased light transmission.

Correct Answer: C

Explanation: Double-paned windows trap a layer of air or inert gas between two panes of glass. This trapped gas is a poor conductor and prevents convection currents, significantly reducing heat transfer by both conduction and convection.

90. What is the term for the total kinetic energy of all the particles in a substance?

A. Temperature. B. Thermal energy. C. Heat capacity. D. Latent heat.

Correct Answer: B

Explanation: Thermal energy refers to the total internal energy of a system due to the motion of its atoms and molecules. It is the sum of the kinetic and potential energies of the particles, but often colloquially used to refer to the kinetic energy component.