Worksheet Solutions: Heat Transfer in Nature

Q.1. True/False

(i) Metals are poor conductors of heat.

Ans: False

Metals are good conductors of heat because they allow heat energy to pass through them quickly.

(ii) Land breeze occurs during the night.

Ans: True

At night, the land cools faster than the sea and the cooler, denser air from the land moves toward the warmer sea, producing a land breeze.

(iii) Dark-colored clothes absorb less heat than light-colored clothes.

Ans:False

Dark-coloured clothes absorb more heat from radiation than light-coloured clothes; light colours reflect more incident radiation.

(iv) Water vapor released by plants is called transpiration.

Ans: True

Transpiration is the process by which plants release water vapour into the air through stomata in their leaves.

(v) Radiation requires air or water to transfer heat.

Ans: False

Radiation is the transfer of heat by electromagnetic waves and can occur through empty space (for example, sunlight reaching the Earth).

Q.2. Fill in the blanks.

(i)  The hotness of an object is determined by its ____.

temperature

(ii) Temperature is measured in degree ____.

celsius

(iii) A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of ____.

conduction

(vi) Dark colored clothes are preferred during ____.

winter

(v) Poor conductors are known as ____.

insulators

Answer the following Questions

Q.3. Does the transfer of heat by radiation require any medium?

The transfer of heat by radiation does not require any medium. Radiation travels as electromagnetic waves and can transfer heat through empty space (for example, the Sun's energy reaches Earth through the vacuum of space).

Q.4. What is the concern associated with the use of mercury thermometers?

There is a lot of concern over the use of mercury in thermometers because mercury is toxic and can harm people and the environment if a thermometer breaks. Mercury is difficult to clean up and dispose of safely. For this reason, many places now use alternatives such as alcohol-based thermometers, digital thermometers, or other safe sensors.

Q.5. How water get heated when kept on flame?

When water is heated from below, the water molecules near the flame gain heat and become less dense.

The warmer water rises upward and cooler, denser water from the sides moves down to replace it.

This cycle of rising warm water and sinking cool water forms a convection current and continues until the whole water is heated.

This mode of heat transfer in liquids is called convection.

Q.6. Which device is used to measure temperature?

Thermometer is used to measure temperature.

Q.7. How does heat flow from one object to another?

Heat flows from a hotter object to a colder object until both reach the same temperature (thermal equilibrium).

Q.8. Do all hot bodies radiate heat?

Yes, all hot bodies emit radiation. Any object with a temperature above absolute zero emits electromagnetic radiation; the amount and type depend on its temperature.

Q.9. How does heat transfer in solids?

In solids, heat is generally transferred by conduction.

In conduction, particles (atoms or molecules) or free electrons in solids vibrate or move and pass energy to neighbouring particles, causing the heat to travel through the solid from the hotter end to the colder end.

Q.10. What is Conduction?

The process by which heat is transferred from the hotter end to the colder end of an object by direct contact is known as conduction.

Q.11. Explain the process of conduction with an example.

Conduction is the transfer of heat in solids through direct contact.

When one end of a solid object is heated, the particles at the hotter end vibrate more strongly and pass some of their energy to neighbouring particles.

Energy is passed along this chain of particles from the hot end to the cold end, so heat travels through the object.

Example: When a metal pan is placed on a flame, the bottom of the pan heats up first.

Heat travels from the bottom to the rest of the pan by conduction, so the pan becomes hot all over.

Metals are commonly used for cooking utensils because they are good conductors of heat; free electrons and closely packed atoms help transfer energy quickly.

Q.12. What is convection and how does it affect coastal areas?

Convection is heat transfer in liquids and gases where warmer, less dense fluid rises and cooler, denser fluid sinks, forming convection currents.

In coastal areas, during the day the land heats faster than the sea. Warm air over the land rises and cooler air from the sea moves in to replace it, producing a sea breeze.

At night the land cools faster than the sea. Air over the sea is relatively warmer and rises, causing cooler air from the land to blow out to the sea as a land breeze.

These daily breezes caused by convection currents moderate coastal temperatures and are felt as comfortable winds.

Q.13. Describe radiation and give two real-life applications.

Radiation is the transfer of heat by electromagnetic waves; it does not require any medium and can occur through vacuum.

Example 1: The Sun heats the Earth by radiation; sunlight carries energy across space to warm land and water.

Example 2: You feel warmth near a fire because the fire radiates heat as infrared and other electromagnetic waves.

Practical note: Light-coloured clothes reflect more radiation and keep us cooler in hot weather, while dark-coloured clothes absorb more radiation and keep us warmer in cold weather.

Q.14. How does the water cycle help in redistributing water on Earth?

The Sun's heat drives the water cycle, which redistributes water across the planet.

Water evaporates from oceans, lakes and rivers as vapour.

Water vapour rises, cools and condenses to form clouds (condensation).

Water falls from clouds as precipitation (rain, snow, sleet) and returns to the surface.

Some of this water flows as surface runoff into rivers and oceans, while some seeps into the ground to become groundwater (infiltration).

This continuous cycle ensures circulation and distribution of water to different regions and supports life on Earth.

Q.15. What are ice stupas and how do they help conserve water in Ladakh?

Ice stupas are man-made, cone-shaped ice structures built in cold regions such as Ladakh to store water as frozen ice during winter.

Water is directed to form tall, conical ice mounds that freeze in winter and melt slowly in spring.

The conical shape reduces surface area relative to volume, causing the ice to melt more slowly and provide a controlled supply of water in the warmer months for irrigation and farming.

Ice stupas are a practical method of conserving and releasing water at the time it is most needed in arid and high-altitude regions.