CBSE Class 7 Science Chapter 07 Heat Transfer In Nature MCQs Set 01

Answer: (B) Pin I falls first because heat reaches it before the others

Explanation:
When the metal strip is heated at one end, heat travels along it through conduction. Pin I, being closest to the heat source, receives heat first, causing the wax holding it to melt and making it fall before the others.

Answer: (B) In conduction, particles remain in place while heat transfers between them; in convection, particles actually move from one location to another

Explanation:
During conduction, heated particles pass thermal energy to adjacent particles without moving themselves. Convection, by contrast, involves the actual movement of particles carrying heat from warmer to cooler regions.

Answer: (B) Clay and porcelain conduct heat away from the drink more slowly because they are poor conductors

Explanation:
Clay and porcelain are poor conductors of heat, meaning they restrict the flow of thermal energy from the hot beverage to the surroundings, keeping the contents warm for an extended period.

Answer: (B) It leads to sea breeze during the day as warm air above land rises and cooler air moves in from the sea

Explanation:
• Land heats and cools faster than water
• During daytime, warm air above the land rises due to this faster heating
• Cooler air from the sea rushes in to replace it, creating a sea breeze that provides relief from heat

Answer: (B) Wood and mud are good insulators that prevent heat loss due to their poor thermal conductivity

Explanation:
Wood and mud are poor conductors of heat. The trapped layer of cow dung and mud between two wooden layers acts as insulation, preventing heat from escaping the house during extremely cold winters.

Answer: (B) Evaporation is the conversion of water from liquid to vapour; transpiration is the release of water vapour from trees and plants

Explanation:
Evaporation is the physical process where water bodies convert liquid water into water vapour due to solar heating. Transpiration refers specifically to the release of water vapour from living plants and trees through their leaves.

Answer: (C) The expansion of air when heated, supporting the explanation of how hot air rises in convection

Explanation:
As sunlight heats the air inside the balloon, the air expands and occupies more space, causing the balloon to inflate. This demonstrates that heating causes air to expand and become less dense, which is why it rises during convection.

Answer: (B) The spaces between gravel particles are wider and more interconnected, allowing water to flow through more easily

Explanation:
Gravel has larger spaces between its particles compared to sand or clay. Water infiltrates more readily through materials with wider, open, interconnected spaces between particles, making gravel the most permeable of the three.

Answer: (C) Light colours reflect most of the radiant heat falling on them, reducing heat absorption by the body

Explanation:
Light-coloured surfaces reflect most of the radiant heat that falls on them. By reflecting rather than absorbing this solar radiation, light-coloured clothes help keep the wearer cooler than dark colours, which absorb more heat.

Answer: (C) Smoke consists of hot gases that are warmer and lighter than surrounding cooler air, causing them to rise through convection

Explanation:
Smoke is a mixture of hot gases and tiny particles. Because these hot gases are warmer than surrounding air, they become less dense and lighter, causing them to rise upward through the natural convection process.

Answer: (C) Infiltration is the seeping of surface water through soil and rocks into the ground, eventually becoming groundwater

Explanation:
Infiltration is specifically the process by which water from the Earth's surface seeps downward through soil and rock layers. This water becomes groundwater, which gets stored in aquifers beneath the surface.

Answer: (B) Heat travels along the metal strip and reaches pins progressively, with those closest to the heat source melting their wax first

Explanation:
Heat moves along the metal through conduction in a progressive manner, travelling from the heated end toward the cooler end. Since pins are arranged at intervals, the wax holding them melts sequentially as the heat reaches each pin, causing them to fall in order.

Answer: (B) Smoke rises upward through convection, so it reaches the ceiling first before dispersing elsewhere in the room

Explanation:
Because hot smoke and gases rise through convection due to being less dense than surrounding cooler air, smoke reaches the ceiling first. Placing a detector there ensures it will detect smoke quickly before the smoke cools and disperses throughout the room.

Answer: (A) • Land and sea absorb solar heat at identical rates • Both breezes blow continuously in the same direction day and night • Sea breeze occurs during day because land heats faster than water, causing warm air to rise and cooler air from the sea to move in • Land breeze occurs at night when cooler land drives warmer air from the sea back toward shore

Explanation:
Land and water absorb and release heat at different rates. During the day, land heats faster than sea, warm air rises over land, and cooler sea air flows in (sea breeze). At night, the situation reverses—land cools faster, so air above the sea rises and cooler land air moves toward the sea (land breeze).

Answer: (B) Water from mountain streams is frozen during winter into a cone-shaped structure that melts slowly during spring as the sun's radiation gradually warms it, providing water throughout the growing season

Explanation:
During winter, water is channeled and frozen into large cone structures called ice stupas. Because the stupa is massive and insulated by its shape and surroundings, the sun's radiation during spring melts it slowly over weeks and months, providing a sustained water supply for farming when streams run dry.

Answer: (B) Conduction, where heat travels through the metal from the hot end towards the colder end

Explanation:
The pins fall sequentially because heat conducts along the metal strip from the heated end to the cooler end. In conduction, particles receive heat and pass it to neighbouring particles without moving from their positions themselves. As heat progressively reaches each pin, the wax holding it melts, causing the pin closest to the flame to fall first.

Answer: (B) Steel is a good conductor; glass and wood are poor conductors

Explanation:
Metals like steel allow heat to pass through them easily and are classified as good conductors of heat. Materials such as glass and wood do not allow heat to pass through them easily, making them poor conductors or insulators. This is why metal cooking utensils are preferred — they efficiently transfer heat to food.

Answer: (B) Air around the flame heats up, expands, becomes lighter, and rises, causing the cup to move upward with it

Explanation:
Hot air becomes lighter and rises because heated air expands and occupies more space, reducing its density. This rising motion of air is the core mechanism of convection. The cup suspended above the candle is carried upward by this rising warm air, demonstrating how convection causes material movement in gases.

Answer: (B) Because during the day, cooler air from the sea moves towards the land as a sea breeze, providing relief from heat

Explanation:
• Land heats faster than water during the day
• Warm air above the land rises, creating lower pressure
• Cooler, denser air from the sea moves towards the land to fill this space
• This sea breeze cools the house and provides comfort in hot regions.

Answer: (B) Convection occurring within the water as heated particles rise and cooler particles descend

Explanation:
The rising and sinking motion of the coloured dye directly shows particle movement within the liquid. Heated water at the bottom expands, becomes less dense, and rises. Cooler water from the sides moves down to replace it, creating a continuous circular motion. This movement of particles transferring heat throughout the water is the definition of convection.

Answer: (B) Soil cools faster than water, just as it heated faster

Explanation:
The chapter explicitly states that soil cools faster than water, mirroring the heating pattern. This differential cooling rate between land and water at night drives the formation of land breezes—as the cooled land becomes cooler than the sea, air movement is reversed compared to daytime patterns.

Answer: (B) Woollen fabric traps air in its pores, and since air is a poor conductor, it prevents heat loss from the body

Explanation:
Air trapped within the pores of woollen fabric acts as an insulator (poor conductor of heat). This trapped air reduces the flow of heat from the body to the surroundings. The same principle explains why layered clothing and air gaps between blankets provide better insulation than a single thick blanket.

Answer: (B) Clay (slowest) → Sand → Gravel (fastest)

Explanation:
Water seeps fastest through gravel because the spaces between gravel particles are wider compared to sand and clay. Wider spaces allow water to flow more easily. Clay has the smallest and most tightly packed spaces, making water seepage very slow. This principle underlies how infiltration rates vary in different soil types beneath Earth's surface.

Answer: (C) Radiation, as the utensil emits heat energy to its surroundings without requiring a medium

Explanation:
All objects, including hot utensils, radiate heat to their surroundings. Unlike conduction and convection, radiation does not depend on a material medium—heat energy travels directly through empty space. This is why hot objects cool even when isolated from contact with other materials or air currents.

Answer: (B) Sun's radiation heats water bodies causing evaporation, and condensation of rising water vapour forms clouds; both processes depend on heat transfer

Explanation:
The Sun's radiation heats oceans, rivers, and lakes, causing evaporation. Water vapour rises and cools as it ascends, condensing into clouds through a reverse heat transfer process. Precipitation returns water to land. This entire sequence depends fundamentally on heat transfer by radiation from the Sun, making solar energy central to sustaining the water cycle.