CBSE Class 7 Science Chapter 07 Heat Transfer In Nature MCQs Set 02

Answer: (B) Metals are good conductors that transfer heat from particle to particle without particles moving from their positions

Explanation:
The chapter explains that metals are good conductors of heat. During conduction, heat passes from one particle to the next in contact, but the particles themselves do not move from their positions. This is why the pin closest to the flame falls first—the heat reaches it first through this sequential particle-to-particle transfer along the metal strip.

Answer: (B) Metals are good conductors of heat, allowing efficient heat transfer from the flame to the food inside

Explanation:
The chapter explicitly states that metals are good conductors of heat and are used for cooking utensils because heat transfers through them efficiently via conduction. This allows the heat from the flame to reach the food being cooked.

Answer: (B) The pins would not fall at all, or only after a much longer time

Explanation:
The chapter states that glass and wood are poor conductors of heat, also called insulators. Unlike metals, these materials do not allow heat to pass through them easily, so the heat from the candle would not travel along the strip efficiently enough to melt the wax holding the pins.

Answer: (D) Radiation from the sun being absorbed differently by sand and water

Explanation:
While all three heat transfer methods occur, the initial heating difference comes from radiation. Activity 7.4 demonstrates that soil heats up faster than water when exposed to sunlight. The chapter notes that sand and soil have different thermal properties than water—sand heats and cools faster.

Answer: (B) Convection, where particles actually move due to differences in density and temperature

Explanation:
The chapter explains that in liquids and gases, heat transfer occurs through convection. Hot water at the bottom expands, becomes lighter, and rises. Cooler, heavier water from the sides moves down to replace it. This actual movement of particles is what creates the visible circulation of the colored dye.

Answer: (B) To take advantage of sea breeze, which brings cooler air to land during the day due to differential heating and cooling rates

Explanation:
During the day, land heats faster than water due to different thermal properties. This causes warm air above the land to rise, pulling cooler air from the sea toward the land—this is sea breeze. By facing windows toward the sea, coastal homes receive this cooling breeze, which the chapter describes as relieving people from heat.

Answer: (C) Radiation from the sun heating the air inside the balloon, causing it to expand

Explanation:
The chapter uses this example to show how air expands when heated. The sun's radiation heats the air inside the balloon, increasing its volume. The balloon enlarges as a result. This illustrates both radiation as the heating mechanism and the expansion property of gases when heated.

Answer: (B) The size and interconnectedness of spaces between particles—gravel has larger, more open spaces than sand or clay

Explanation:
The chapter explains that water infiltrates more readily when spaces between soil and rock particles are wider, open, and interconnected. Gravel has larger gaps between its particles compared to sand, which has smaller gaps, and clay has even tighter packing. This is why water seeps fastest through gravel and slowest through clay.

Answer: (B) Dark surfaces absorb more heat while light surfaces reflect it, so dark clothing in winter absorbs body heat and light clothing in summer reflects solar heat

Explanation:
The chapter's section on radiation explicitly states that light-coloured clothes reflect most of the heat that falls on them, making them comfortable for summers, while dark surfaces absorb more heat, making dark-coloured clothes more comfortable for winters when we want to retain body heat.

Answer: (B) Upward, because smoke consists of hot gases and particles that are warmer and lighter than surrounding air

Explanation:
The chapter describes smoke as a mixture of hot gases and tiny solid particles. Because it is warmer than the surrounding air, it becomes lighter through convection and rises upward, even when the incense stick points downward. This is the same principle that makes smoke rise from a fireplace.

Answer: (C) Wood and mud are poor conductors (insulators) that prevent heat loss from inside the house to the cold outside environment

Explanation:
The Fascinating Facts section explains that wood and mud are poor conductors of heat. By using them as walls with an air gap between layers, heat loss from the warm interior to the cold exterior is prevented, thereby keeping the houses warm during extremely cold winters.

Answer: (B) Evaporation occurs from water surfaces while transpiration occurs from trees and plants

Explanation:
The chapter's section on the water cycle clearly distinguishes these processes: water evaporates from oceans, rivers, and lakes due to the sun's heat, while water also evaporates from trees and plants through transpiration. Both contribute to atmospheric water vapour but occur from different sources.

Answer: (B) Rainwater harvesting and recharge pits that allow water to infiltrate back into the ground

Explanation:
The chapter states that rainwater harvesting and recharge pits are used to replenish groundwater. These systems allow water to infiltrate through the soil back into aquifers. The water cycle itself continuously recharges groundwater sources through precipitation and infiltration when conditions permit.

Answer: (C) Radiation, because it can transfer heat without requiring any material medium

Explanation:
The chapter explicitly states in its summary that in conduction and convection, a medium must be present whose particles help transfer heat. However, in radiation, heat travels from one place to another without any material medium being required. Heat from the sun reaches Earth through radiation across the vacuum of space, illustrating this principle.

Answer: (B) Smoke rises due to convection currents created by heated air, so it reaches the ceiling first before spreading throughout the room

Explanation:
The chapter explains that hot air and smoke rise due to convection. When something burns, the heat causes air to expand and become lighter, causing it to rise upward. Therefore, smoke from a fire will reach the ceiling first, making it the most effective location to detect smoke early.

Answer: (B) Conduction, where each particle transfers heat to its neighbour without the particles themselves moving to new positions

Explanation:
The chapter explicitly states that in conduction, a particle that gets heated passes heat to its neighbour, and so on, but the particles themselves do not move from their positions. This mechanism explains why pins closer to the heat source fall first — the heat travels along the strip by particle-to-particle transfer, not by the movement of particles themselves.

Answer: (B) Heat moves progressively from the heated end towards the cooler end, taking time to reach each successive pin

Explanation:
In conduction, heat transfers from hot to cold regions by particle-to-particle contact without the particles themselves migrating. Since the pins are attached at roughly equal intervals along the strip, the progressive arrival of heat at each pin causes them to fall in sequence rather than all at once. The heated end warms first, then the heat gradually conducts towards the cooler end, melting the wax holding each pin in turn.

Answer: (B) Newspaper is a poor conductor that slows heat transfer to the customer's hand

Explanation:
Poor conductors of heat, also called insulators, prevent heat from passing through them easily. Newspaper traps air in its fibrous structure, and since air is a poor conductor of heat, it reduces the rate at which heat flows from the hot cup to the customer's hand, making it comfortable to hold.

Answer: (B) During the day, cooler sea air moves toward the heated land, creating what is called a sea breeze

Explanation:
Land heats and cools faster than water. During the day, the sun heats the sand or soil faster than the seawater, causing warm air above the land to rise. This creates lower pressure at the surface, allowing cooler air from the sea to move inland—this movement is called a sea breeze. At night, the process reverses, creating a land breeze.

Answer: (A) The ice stupa stores frozen water that melts slowly over several months, gradually releasing water as the sun's radiation heats it

Explanation:
The ice stupa is constructed to accumulate water during winter when streams normally freeze and run dry. When spring sun radiates heat onto the stupa, the ice melts gradually due to the large mass and structure of the cone. This slow melting releases water continuously throughout the warmer months when farming and other activities require it most, solving the seasonal water scarcity problem.

Answer: (C) Both conduction and convection require a medium, but radiation does not

Explanation:
Conduction and convection both depend on matter—particles of solids, liquids, or gases—to transfer heat through their movement or vibration. Radiation, however, transfers heat through electromagnetic waves that can travel through empty space without any medium. The warmth from a fireplace or the sun reaching Earth demonstrates that radiation needs no material to carry heat.

Answer: (B) Clay, sand, gravel

Explanation:
The spaces between particles determine how readily water can seep through. Clay particles are fine and tightly packed, leaving small interconnected spaces, so water passes very slowly. Sand has medium-sized particles with moderate spacing. Gravel particles are large, creating the widest open spaces and allowing water to flow most rapidly. Infiltration rate increases as pore space increases.

Answer: (B) Light surfaces reflect most of the radiant energy from the sun, while dark surfaces absorb more of this radiation

Explanation:
Through the process of radiation, the sun's energy reaches Earth directly without needing a medium. Light-coloured surfaces reflect most of the radiant energy that falls on them, allowing it to bounce away. Dark surfaces, conversely, absorb more of the radiant heat energy, causing their temperature to increase more rapidly. This is why wearing dark clothes in winter feels warmer and light clothes in summer feel cooler.

Answer: (B) On the ceiling, where hot smoke rises and accumulates due to convection

Explanation:
Hot gases, including smoke, expand and become less dense when heated, causing them to rise due to convection. Smoke from a fire consists of hot gases and particles that naturally move upward. Placing a detector on the ceiling ensures it intercepts the rising smoke early, allowing for faster fire detection and response, which is critical for safety.

Answer: (B) Heat is conducted progressively along the metal strip from the heated end towards the cooler end

Explanation:
In conduction, heat travels from one part of a solid to an adjacent cooler part through particle-to-particle transfer without the particles themselves moving. As heat travels along the strip, it reaches pin I first, causing its wax to melt and the pin to fall. Then heat reaches pin II, and so on. The sequential falling directly shows that heat is progressively conducted from the heated end towards the cooler end along the length of the strip, not reaching all pins at once.