Heat and Temperature MCQs 91 to 120 Questions with details Answers.

Heat and Temperature MCQs 91 to 120

91. What is the primary purpose of insulation in a building?

A. To reduce heat transfer between inside and outside. B. To increase the building's structural strength. C. To absorb sunlight. D. To make walls soundproof.

Correct Answer: A

Explanation: Insulation materials are poor conductors of heat, designed to minimize heat flow, keeping buildings warmer in winter and cooler in summer by reducing heat loss or gain.

92. Which of the following best describes the process of sublimation?

A. Solid turning directly into liquid. B. Liquid turning directly into gas. C. Gas turning directly into liquid. D. Solid turning directly into gas.

Correct Answer: D

Explanation: Sublimation is a phase transition where a substance changes directly from a solid to a gas without passing through a liquid phase, like dry ice (solid carbon dioxide) at room temperature.

93. Why does a bimetallic strip bend when heated?

A. Both metals expand equally. B. The two metals have different coefficients of thermal expansion. C. Heat causes one metal to contract. D. It is designed to be flexible.

Correct Answer: B

Explanation: A bimetallic strip consists of two different metals bonded together. When heated, they expand at different rates (due to different coefficients of thermal expansion), causing the strip to bend towards the side of the metal with lower expansion.

94. What is the primary function of a thermostat?

A. To generate heat. B. To measure temperature. C. To regulate temperature. D. To insulate a system.

Correct Answer: C

Explanation: A thermostat is a device that automatically regulates temperature, often by turning heating or cooling systems on or off when the temperature deviates from a set point.

95. Why does a hot air balloon float?

A. Hot air is less dense than the surrounding cooler air. B. The balloon is filled with a lighter-than-air gas. C. It uses a propulsion system. D. It creates a vacuum inside.

Correct Answer: A

Explanation: Heating the air inside the balloon makes it less dense than the cooler air outside. This difference in density creates an upward buoyant force, causing the balloon to float.

96. What is the effect of increasing the surface area of a liquid on its rate of evaporation?

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

Correct Answer: C

Explanation: A larger surface area exposes more liquid molecules to the air, allowing more of them to escape into the gaseous phase, thus increasing the rate of evaporation.

97. Why do farmers spray water on their crops during a cold night to protect them from frost?

A. The latent heat released when water freezes protects the plants. B. Water absorbs heat from the plants. C. Water prevents the plants from drying out. D. The ice layer acts as a conductor of warmth.

Correct Answer: A

Explanation: When water freezes, it releases a significant amount of latent heat of fusion. This released heat warms the surrounding air and the plants, preventing their temperature from dropping below freezing and protecting them from frost damage.

98. What is the phenomenon where a substance changes directly from gas to solid?

A. Evaporation. B. Melting. C. Condensation. D. Deposition.

Correct Answer: D

Explanation: Deposition is the phase transition from gas directly to solid, bypassing the liquid phase. An example is the formation of frost on cold surfaces when water vapor in the air directly turns into ice crystals.

99. Why is a vacuum flask (thermos) effective at keeping liquids hot or cold?

A. It uses a strong magnetic field. B. It minimizes heat transfer by conduction, convection, and radiation. C. It actively heats or cools the contents. D. It has a very thick wall.

Correct Answer: B

Explanation: A vacuum flask has a double-walled construction with a vacuum between the walls (reducing conduction and convection) and silvered surfaces (reducing radiation), effectively minimizing all three modes of heat transfer.

100. What is the effect of increasing pressure on the melting point of most substances?

A. It increases. B. It decreases. C. It remains constant. D. It becomes undefined.

Correct Answer: A

Explanation: For most substances, increasing pressure makes it harder for particles to break free from the solid lattice, thus requiring a higher temperature (increased melting point) to transition to a liquid.

101. Why does a hot object cool down faster in a drafty room than in a still room?

A. Radiation is more effective in a draft. B. Conduction is increased. C. Convection is enhanced, carrying away heat more rapidly. D. The object's specific heat capacity changes.

Correct Answer: C

Explanation: A draft (moving air) increases the rate of convection. The moving air constantly carries away the heated air from around the object, replacing it with cooler air, thus accelerating the cooling process.

102. What is the difference between heat and temperature?

A. Heat is the average kinetic energy, temperature is the total. B. Heat is energy transfer, temperature is a measure of average kinetic energy. C. They are interchangeable terms. D. Heat is measured in Celsius, temperature in Joules.

Correct Answer: B

Explanation: Heat is the transfer of thermal energy between objects due to a temperature difference, while temperature is a measure of the average kinetic energy of the particles within a substance.

103. Why are igloos effective at keeping people warm?

A. Snow and ice are good insulators, trapping air. B. The ice actively generates heat. C. They are heated by internal fires. D. They are built on warm ground.

Correct Answer: A

Explanation: Snow and ice, particularly packed snow, contain a lot of trapped air. Trapped air is an excellent thermal insulator, which significantly reduces heat loss from inside the igloo to the cold exterior.

104. What is the principle behind a hot water bag used for pain relief?

A. It creates a vacuum. B. It generates cold. C. It transfers heat by conduction to the affected area. D. It uses convection currents.

Correct Answer: C

Explanation: A hot water bag works by direct contact. The heat from the hot water is transferred to the body through conduction, which helps to relax muscles and alleviate pain.

105. Why does a metal chair feel colder than a wooden chair in the same room?

A. Metal has a lower temperature. B. Metal is a better conductor of heat than wood. C. Wood generates heat. D. Metal reflects heat.

Correct Answer: B

Explanation: Both chairs are at room temperature. However, metal is a good conductor of heat, so it rapidly conducts heat away from your hand, making it *feel* colder. Wood is an insulator, so it conducts heat away much more slowly.

106. What is the purpose of a cooling fan in electronic devices?

A. To dissipate heat through forced convection. B. To generate cold air. C. To absorb static electricity. D. To increase the device's speed.

Correct Answer: A

Explanation: Electronic components generate heat during operation. A cooling fan creates forced convection by moving air over the hot components, which carries the heat away more efficiently and prevents overheating.

107. What happens to the volume of water when it freezes to ice?

A. It decreases. B. It remains the same. C. It increases. D. It first decreases then increases.

Correct Answer: C

Explanation: Water is unusual because its solid form (ice) is less dense than its liquid form. This means that when water freezes, its volume increases, which is why pipes can burst in freezing temperatures.

108. Which color is generally the best emitter of thermal radiation?

A. White. B. Black. C. Silver. D. Red.

Correct Answer: B

Explanation: Good absorbers of thermal radiation are also good emitters. Black surfaces absorb nearly all incident radiation, and conversely, they are very efficient at emitting thermal radiation.

109. What is the main reason for the formation of sea breezes during the day?

A. Land heats up faster than water, causing air to rise over land. B. Water heats up faster than land. C. The Earth's rotation. D. High pressure over the sea.

Correct Answer: A

Explanation: Land has a lower specific heat capacity than water, so it heats up more quickly during the day. The warmer air over the land rises, creating a low-pressure area, and cooler, denser air from over the sea moves in to replace it, forming a sea breeze.

110. What type of energy is transferred during a phase change (e.g., melting or boiling)?

A. Kinetic energy. B. Electrical energy. C. Chemical energy. D. Latent heat.

Correct Answer: D

Explanation: During a phase change, the temperature of the substance remains constant. The energy absorbed or released is called latent heat, which is used to change the state (e.g., break intermolecular bonds during melting or boiling) rather than increase kinetic energy.

111. Why do desert regions experience large temperature differences between day and night?

A. High humidity. B. Low specific heat capacity of sand and lack of water vapor. C. Strong winds. D. High levels of vegetation.

Correct Answer: B

Explanation: Sand has a low specific heat capacity, meaning it heats up and cools down quickly. Additionally, the lack of water vapor in desert air (which acts as a greenhouse gas) means there's little to trap heat at night, leading to rapid cooling.

112. What is the process by which heat is transferred through the movement of fluids (liquids or gases)?

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

Correct Answer: A

Explanation: Convection involves the transfer of heat by the actual movement of heated fluid particles. As fluids are heated, they become less dense and rise, while cooler, denser fluid sinks, creating a convection current.

113. Why are clothes made of wool or down effective in keeping us warm?

A. They generate heat. B. They are good conductors of heat. C. They trap air, which is a poor conductor of heat. D. They are reflective.

Correct Answer: C

Explanation: Wool and down fibers are structured in a way that traps a significant amount of air within their matrix. This trapped air acts as an excellent insulator, reducing heat loss from the body by conduction and convection.

114. What is the process of heat transfer that does not require a medium?

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

Correct Answer: D

Explanation: Radiation is the transfer of heat in the form of electromagnetic waves. Unlike conduction and convection, it does not require any physical medium for transfer and can occur through a vacuum.

115. What is the main reason for the formation of land breezes at night?

A. Land cools down faster than water, causing air to sink over land. B. Water cools down faster than land. C. The moon's gravitational pull. D. Low pressure over the sea.

Correct Answer: A

Explanation: At night, land cools down more quickly than water due to its lower specific heat capacity. The cooler, denser air over the land sinks, creating a high-pressure area, and flows towards the relatively warmer, lower-pressure area over the sea, forming a land breeze.

116. What is the effect of adding impurities to a liquid on its boiling point?

A. It decreases. B. It increases. C. It remains constant. D. It first increases then decreases.

Correct Answer: B

Explanation: Adding impurities (solutes) to a liquid elevates its boiling point. This is because the impurities interfere with the solvent molecules escaping into the vapor phase, requiring more energy (higher temperature) to reach the boiling point.

117. How does a refrigerator cool its contents?

A. It generates cold. B. It adds ice to the food. C. It removes heat from the inside and releases it outside. D. It converts heat into light.

Correct Answer: C

Explanation: A refrigerator does not "generate cold." Instead, it uses a refrigerant to absorb heat from the inside compartment (making it cold) and then expels that heat to the warmer surroundings outside the refrigerator.

118. What is the term for the transfer of heat from a warmer object to a cooler object?

A. Heat flow. B. Temperature increase. C. Thermal equilibrium. D. Specific heat.

Correct Answer: A

Explanation: Heat flow (or heat transfer) is the natural process by which thermal energy moves from a region of higher temperature to a region of lower temperature.

119. Why are dark-colored clothes generally avoided in hot climates?

A. They are less durable. B. They absorb more solar radiation, making the wearer hotter. C. They are heavier. D. They reflect too much heat.

Correct Answer: B

Explanation: Dark colors are good absorbers of radiant heat, including sunlight. Wearing dark clothes in hot climates means they absorb more solar energy, which then transfers to the body, making the wearer feel hotter.

120. What is the state of matter where particles are closely packed but can slide past each other?

A. Gas. B. Solid. C. Liquid. D. Plasma.

Correct Answer: C

Explanation: In a liquid, particles are close together but have enough kinetic energy to overcome some intermolecular forces, allowing them to move and slide past one another, giving liquids their fluid properties.