CBSE Class 7 Science Chapter 07 Heat Transfer In Nature MCQs Set 03

Answer: (B) Metals are good conductors of heat, allowing thermal energy to pass from particle to particle

Explanation:
The chapter defines good conductors of heat as materials that allow heat to pass through them easily. In the pin-drop activity, heat travels along the metal strip through conduction, where each heated particle passes thermal energy to its neighboring particle. This allows heat to reach successive pins in order, causing their wax to melt sequentially rather than all at once.

Answer: (B) Metals conduct heat efficiently, transferring thermal energy from the flame to the food being cooked

Explanation:
The chapter explicitly states that metals are good conductors of heat and that because of this property, metal utensils are used for cooking. In solids, heat transfer takes place mainly through the process of conduction, which is efficient in metals. This allows heat to quickly reach the food being prepared in the vessel.

Answer: (B) The air around the candle heats up, expands, becomes lighter, and rises, pushing the cup upward

Explanation:
The chapter explains that when air around the candle flame heats up, it expands and occupies more space. As a result, it becomes lighter (less dense) and rises upward. This rising hot air pushes the suspended cup upward, demonstrating the convection principle where heated fluids move due to density differences.

Answer: (C) Convection is taking place as heated water rises and cooler water sinks

Explanation:
• Water at the bottom gets heated and expands, becoming lighter
• It rises toward the top due to lower density
• Cooler water from the sides is heavier and descends to replace rising water
• This continuous cycle demonstrates convection—heat transfer by actual movement of fluid particles rather than particle-to-particle contact as in conduction

Answer: (B) The specific heat capacity of soil is lower than that of water, so it experiences greater temperature change for the same amount of heat

Explanation:
The chapter demonstrates through Activity 7.4 that soil heats up faster than water when both receive equal solar radiation. Though the chapter does not explicitly state "specific heat capacity," it shows that soil undergoes greater temperature increases in shorter time periods. This difference in heating and cooling rates is what creates land breezes and sea breezes in coastal areas.

Answer: (C) Sea breeze

Explanation:
The chapter clearly defines sea breeze as the movement of cooler air from the sea to the land, occurring during the day when land heats up faster than water. This happens because the warmer air above the land rises due to convection, creating a pressure difference that pulls in cooler, heavier air from over the sea.

Answer: (B) Smoke rises due to convection, so it reaches the ceiling before spreading elsewhere in the room

Explanation:
Since smoke is a mixture of hot gases and particles that are warmer than surrounding air, it rises upward through convection. By placing a detector on the ceiling, it can detect rising smoke most effectively as the heated smoke naturally moves upward through the room before it cools and spreads laterally.

Answer: (B) Clay, Sand, Gravel

Explanation:
The chapter states that water seeps fastest through gravel, slower through sand, and slowest through clay. This is because the spaces between gravel particles are wider compared to those in sand and clay, allowing water to move through more easily. The pore space sizes directly determine infiltration rates.

Answer: (C) Radiation, as the sun's heat directly causes the air inside to expand

Explanation:
Radiation is the transfer of heat without requiring a medium. The sun's radiant energy directly heats the air inside the balloon, causing it to expand and occupy more space. The balloon becomes larger because the heated air occupies greater volume—a direct consequence of heat transfer through radiation from the sun.

Answer: (B) Air is a poor conductor of heat, reducing heat flow away from the body

Explanation:
The chapter explicitly states that air is a poor conductor of heat. When woollen fabric traps air in its pores, this poor-conducting air acts as an insulator. Similarly, air trapped between layers of clothing reduces heat flow from the body to the surroundings, helping us feel warmer. This is why multiple thin blankets with air gaps are preferred over one thick blanket.

Answer: (B) Air trapped in the hollow spaces is a poor conductor of heat, preventing external heat from entering

Explanation:
Similar to how the chapter explains that air trapped in blankets acts as an insulator, air trapped within hollow bricks serves the same function. As a poor conductor of heat, this trapped air prevents or significantly reduces the flow of thermal energy from outside through the brick walls into the interior of the house.

Answer: (C) Light-coloured clothes reflect most incoming heat, while dark-coloured clothes absorb more heat

Explanation:
The chapter's "Dive Deeper" section explains that light-coloured clothes reflect most of the heat that falls on them, which is why they are comfortable for summers. Conversely, dark surfaces absorb more heat, making dark-coloured clothes more suitable for winters when we want to retain body warmth. This demonstrates how radiation heat transfer and surface colour properties affect thermal comfort.

Answer: (B) Radiation from the sun provides the energy for evaporation and also enables cooling at higher altitudes through radiation loss

Explanation:
The sun transfers heat through radiation, which energizes water molecules in oceans and lakes, causing evaporation. As water vapour rises, it eventually cools—this cooling occurs partly through radiation to space. The temperature difference drives the water cycle continuously, with the sun's radiant energy being the ultimate energy source for the entire process.

Answer: (C) The size and connectivity of pore spaces between particles

Explanation:
The chapter explicitly states that gravel particles have wider spaces between them compared to sand and clay. Water can infiltrate more readily if the spaces between soil and rock particles are wider, open, and interconnected. Larger pore spaces allow water to flow through more easily, explaining why gravel allows faster seepage than clay or sand.

Answer: (B) The sun's radiant heat slowly melts the ice stupa during spring and summer, releasing stored water at a controlled rate over several months

Explanation:
The ice stupa stores water in frozen form during cold winters. As spring and summer arrive, the sun's radiation gradually heats and melts the ice stupa. Because the large structure melts slowly, it provides a sustained water supply throughout the warmer months rather than releasing all water at once. This demonstrates how understanding heat transfer allows communities to manage seasonal water scarcity through thermal storage principles.

Answer: (C) Evaporation is water entering the atmosphere from water bodies, while transpiration is water entering the atmosphere from trees and plants

Explanation:
Though both processes add water vapour to the atmosphere, they have distinct sources: evaporation comes from water bodies like oceans and rivers, while transpiration specifically refers to water loss from vegetation through their leaves.