Solutions-NCERT-Class-7-Science-Curiosity-Chapter-7-Heat Transfer in Nature-CBSE

• Smoke rises because of convection.
• When fire heats the air, the hot air becomes lighter and moves upward.
• The smoke also moves up with the hot air.
• Cooler air comes down to take its place, and this process keeps repeating.

• In liquids, heat is transferred by convection.
• When a liquid is heated from below, the particles near the heat source become hot, expand, and become lighter, so they move upward.
• Cooler and heavier liquid moves down to take their place. This cycle continues and slowly heats the whole liquid.

• Water seeps into the Earth through the spaces between soil and rocks. This process is called infiltration.
• Water moves faster through gravel because it has bigger spaces, and slower through clay because it has very small spaces.
• The seeped water gets stored underground in layers of rock and soil called aquifers.

(c) A is a good conductor and B is a poor conductor of heat.

Explanation : The body of the pan (A) must conduct heat to the food, while the handle (B) must be an insulator so it can be held safely.

(b) Pins I and II will fall earlier than pins III and IV.

Explanation : Heat travels sequentially from the hotter end of the metal strip to the colder end, melting the wax holding the closest pins first.

(c) On the ceiling.

Explanation : Because smoke is warmer than the surrounding air, it expands, becomes lighter, and rises upward.

Yes, this arrangement will help keep the lassi cold for a longer time.

When one tumbler is placed inside another, a layer of air is trapped between them. Since air is a poor conductor of heat, it acts as an insulator that reduces the flow of heat from the warm surroundings to the cold lassi.

(i) False. (Heat transfer in solids takes place mainly through conduction, not convection.)

(ii) True.

(iii) False. (Clay has very fine particles with minimal space, meaning it has the slowest seepage rate, whereas sandy materials have wider spaces and allow faster seepage.)

(iv) True.

• The ice cubes get heat for this transformation from their surroundings.
• All objects, including the dish and the air in the room, radiate heat. This heat is transferred to the colder ice cubes, causing them to melt.

The smoke will move upward. Even if the stick points down, smoke is a mixture of hot gases that are warmer and lighter than the surrounding air, causing it to rise.

• The thermometer in Fig. (a) will record a higher temperature more effectively. When water is heated from the bottom, the hot water rises and cooler water moves down to take its place, creating convection currents that heat the entire volume.
• In Fig. (b), heating from the top prevents these currents because the warm water simply stays at the top.

• Hollow bricks are used because they trap air within their structures.
• Since air is a poor conductor of heat, it acts as an effective insulator that reduces the transfer of outside heat into the house, keeping the interior cooler.

• Large water bodies prevent extreme temperatures because water heats up and cools down much more slowly than land.
• During the day, cooler air from the sea (sea breeze) moves toward the land to relieve the heat, and at night, the process reverses (land breeze), helping to balance the climate in coastal areas.

• Water seeps through the Earth's surface by passing through the spaces between soil and rock particles, a process known as infiltration.
• It infiltrates most readily where spaces are wide and interconnected, eventually being stored in the pore spaces of underground rocks and sediments called

• The water cycle is essential because it involves the continuous movement of water upward as vapour and downward as precipitation.
• This process redistributes water from oceans to land and replenishes rivers, lakes, and groundwater supplies, ensuring the total amount of water on Earth is conserved and made available for life.