CBSE Class 7 Science Revision Notes Chapter 7: Heat Transfer in Nature

Heat moves from a hotter region to a colder region through conduction, convection or radiation. These processes also explain cooking, winds near the coast, house design, clothing and the movement of water in nature.

Heat from the Sun affects temperature, winds, evaporation and the water cycle. We also experience heat transfer while cooking food, sitting near a fire, wearing woollen clothes or touching a metal spoon placed in hot water.

These CBSE Class 7 Science Revision Notes Chapter 7 follow the current 2026–27 chapter. Revise conduction, convection, radiation, land and sea breeze, the water cycle, infiltration, groundwater and aquifers. The chapter also explains how insulation, house design and water-conservation methods use these scientific principles.

Key Takeaways

• Conduction: Heat passes from particle to particle without the particles changing position.
• Convection: Heat is transferred through the movement of particles in liquids and gases.
• Radiation: Heat travels without requiring a material medium.
• Groundwater: Infiltrated water is stored in pore spaces and openings within underground sediments and rocks.

Access Class 7 Science Chapter 7 Heat Transfer in Nature Notes in 30 Minutes

Spend the first 10 minutes revising conduction, good conductors, poor conductors and insulation. Use the next 10 minutes for convection, land breeze, sea breeze and radiation.

Use the final 10 minutes to revise the water cycle, infiltration, groundwater, aquifers, recharge methods and ice stupas.

Need help revising heat transfer and the water cycle?

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Heat Transfer in Class 7 Science Chapter 7 Notes

Heat naturally moves from a hotter body or region to a colder one. This transfer continues until the temperature difference becomes smaller.

The three main methods of heat transfer are:

• Conduction
• Convection
• Radiation

Different materials and situations may involve one or more of these methods.

Conduction of Heat

Conduction is the transfer of heat from the hotter part of an object to its colder part. During conduction, particles transfer heat to neighbouring particles but do not move away from their positions.

This method mainly occurs in solids.

Metal Strip and Pins Activity

Four pins are attached to a metal strip using wax. One end of the strip is heated with a candle.

The pin closest to the flame falls first because heat reaches it first and melts the wax. The remaining pins fall one after another as heat travels farther along the strip.

The order is:

Pin I → Pin II → Pin III → Pin IV

This proves that heat moves gradually from the hotter end to the colder end.

Why Do All Pins Not Fall Together?

Heat takes time to travel along the metal strip. The part closest to the flame becomes hot first, while the farther parts heat up later.

Therefore, the wax under each pin melts at a different time.

Good and Poor Conductors of Heat

Materials differ in their ability to transfer heat. Those that allow heat to pass easily are called good conductors, while those that slow down heat transfer are called poor conductors or insulators.

Good Conductors

Most metals are good conductors of heat.

Examples include:

• Iron
• Aluminium
• Copper
• Steel

This is why cooking vessels are usually made of metals.

Poor Conductors

Materials such as wood, glass, clay, porcelain and air do not transfer heat easily.

They are used where heat transfer needs to be reduced.

Examples in Daily Life

Why Woollen Clothes Keep Us Warm

Woollen fabric contains many small pores that trap air. Air is a poor conductor of heat, so it slows down the transfer of body heat to the colder surroundings.

Wool does not produce heat. It helps retain the heat already produced by the body.

Why Can Two Thin Blankets Work Better?

Two thin blankets trap a layer of air between them. This extra layer acts as an insulator and reduces heat loss.

One thick blanket may trap less air between separate layers, so two thin blankets can sometimes feel warmer.

Heat Transfer and House Design

Houses in extremely hot or cold regions often use poor conductors in their walls. Materials such as wood, mud and trapped air reduce the flow of heat between indoors and outdoors.

In cold Himalayan regions, some traditional houses have double wooden walls filled with mud and cow dung. Hollow bricks also contain trapped air and help keep houses warmer in winter and cooler in summer.

Convection in Air and Water

Convection is the transfer of heat through the actual movement of particles in a liquid or gas. When part of a liquid or gas is heated, it expands, becomes lighter and rises.

Cooler and heavier particles move down to take its place. This repeated movement forms a convection current.

Convection in Air

Air near a flame becomes heated and expands. The warm air becomes lighter and rises, while cooler air moves in to replace it.

This explains why:

• Smoke rises
• Hot air balloons rise
• Air near a heater moves upwards
• Smoke detectors are placed near ceilings

Paper Cup Activity

Two inverted paper cups are balanced on a wooden stick. A candle is placed below one cup.

The air below that cup heats up, expands and rises. The upward-moving warm air pushes the cup up and disturbs the balance.

Balloon in Sunlight

Air inside a partially inflated balloon expands when heated by sunlight. The balloon becomes larger because the warm air occupies more space.

Convection in Water

Water also transfers heat through convection. When water at the bottom of a beaker is heated, it expands, becomes lighter and rises.

Cooler water near the sides moves down to replace it. This cycle continues until the entire volume of water becomes warm.

Potassium Permanganate Activity

A small grain of potassium permanganate is placed at the bottom of a beaker filled with water. When the beaker is heated from below, a coloured streak rises from the centre and moves down along the sides.

The movement shows the path of convection currents in water.

Land and Sea Breeze

Land and water do not heat and cool at the same rate. Land heats up and cools down faster than water.

This difference creates local winds near coastal areas.

Sea Breeze

During the day, land heats up faster than the sea. The air above the land becomes warm and rises.

Cooler air from the sea moves towards the land to replace it. This movement is called sea breeze.

Direction: Sea → Land

Sea breeze helps reduce daytime heat in coastal areas. Houses near the coast may have windows facing the sea to allow cooler air inside.

Land Breeze

At night, land cools faster than the sea. The water remains comparatively warmer, so the air above the sea rises.

Cooler air from the land moves towards the sea. This movement is called land breeze.

Direction: Land → Sea

Land and Sea Breeze Comparison

Why Coastal Areas Have Milder Temperatures

Large water bodies heat and cool more slowly than land. During the day, they reduce extreme heating, and at night, they release stored heat gradually.

This helps coastal areas avoid the extreme temperature changes often experienced in inland regions.

Radiation in Heat Transfer Notes

Radiation is the transfer of heat without the need for a material medium. Heat from the Sun reaches the Earth through radiation because space between them does not contain a continuous material medium.

We also feel radiation while sitting near a fire or standing close to a hot utensil.

All Objects Radiate Heat

A hot object loses heat to its surroundings through radiation. This is why a hot utensil gradually cools even when it is not touching a colder object.

Objects can both absorb and emit radiant heat.

Light and Dark-Coloured Surfaces

Light-coloured surfaces reflect more heat and absorb less. This is why light-coloured clothes are more comfortable during summer.

Dark surfaces absorb more heat. Dark-coloured clothes can therefore feel warmer during winter.

Everyday Applications

• White clothes in summer
• Dark clothes in winter
• Light-coloured roofs in hot regions
• Dark solar cooker surfaces
• Reflective coverings to reduce heating

Conduction, Convection and Radiation Together

Several daily-life situations involve all three methods of heat transfer at the same time.

When water is heated in a metal pan:

• Heat moves through the metal pan by conduction.
• Water circulates and heats through convection.
• Heat from the flame and hot pan reaches the surroundings by radiation.

Bukhari

A bukhari is a traditional room heater used in Himalayan regions. Wood or charcoal burns inside an iron stove, while a chimney carries smoke outside.

It involves all three heat-transfer processes:

• Conduction through the metal body
• Convection of warm air in the room
• Radiation from the hot stove

Heat Transfer Comparison

Water Cycle in Class 7 Science Chapter 7 Revision Notes

Water exists naturally in solid, liquid and gaseous forms. It continuously moves between the Earth’s surface and the atmosphere.

This continuous movement is called the water cycle.

Main Stages of the Water Cycle

Evaporation

Heat from the Sun changes water from oceans, rivers, lakes and ponds into water vapour.

Wet clothes also dry faster on sunny days because heat increases evaporation.

Transpiration

Plants release water vapour through their leaves. This process is called transpiration.

Evaporation and transpiration together add water vapour to the atmosphere.

Condensation

As water vapour rises, it enters cooler regions of the atmosphere. It cools and changes into tiny water droplets.

These droplets gather to form clouds.

Precipitation

Water returns to the Earth as rain, snow or hail. This process is called precipitation.

The water then flows into rivers, lakes and oceans or seeps into the soil.

Collection and Return

Water flowing over land reaches ponds, rivers, lakes and seas. Some water enters the ground and becomes groundwater.

The Sun heats surface water again, and the cycle continues.

Importance of the Water Cycle

The water cycle:

• Redistributes water
• Replenishes rivers and lakes
• Recharges groundwater
• Supports plants and animals
• Maintains the total amount of water on Earth
• Connects the atmosphere, land and water bodies

Infiltration and Groundwater

Some rainwater flows over the surface, while some seeps into soil and rocks. The process by which surface water enters the ground is called infiltration.

The rate of infiltration depends on the size and connection of spaces between particles.

Seepage through Clay, Sand and Gravel

Water moves differently through different materials.

Gravel allows water to pass fastest because it has wider and more connected spaces. Clay holds water more tightly because its particles are packed closely.

What Is Groundwater?

Water that seeps below the Earth’s surface and becomes stored in spaces between sediments and cracks in rocks is called groundwater.

It can be accessed through:

• Wells
• Handpumps
• Borewells

The depth of groundwater may vary from a few metres to hundreds of metres depending on the location.

What Is an Aquifer?

An aquifer is an underground layer of sediments or rocks that stores groundwater in its pore spaces and openings.

Wells and borewells are dug or drilled into aquifers to obtain water.

Difference between Infiltration, Groundwater and Aquifer

Groundwater Depletion

Groundwater is limited and can be depleted when extraction happens faster than recharge.

Major causes include:

• Growing population
• Excessive pumping
• Increasing water demand
• Reduced vegetation
• Concrete roads and buildings
• Fewer open soil surfaces
• Lower infiltration

Urban construction covers the ground with concrete, reducing the amount of rainwater that can seep into the soil.

Groundwater Recharge

Groundwater recharge means adding water back to underground reserves.

Methods include:

• Rainwater harvesting
• Recharge pits
• Percolation tanks
• Open green spaces
• Protecting ponds and lakes
• Increasing vegetation
• Reducing unnecessary extraction

Recharge pits collect rainwater and allow it to seep gradually into the ground.

Varahamihira and Rainfall Study

Varahamihira was a sixth-century astronomer and mathematician from Ujjaini, now called Ujjain. In his work Brihatsamhita, he described methods of predicting seasonal rainfall.

His observations included cloud formation, wind patterns, the Moon, stars and other natural events.

Ice Stupas and Water Conservation

Ice stupas are cone-shaped ice structures created in Ladakh to store winter water for use during spring and summer.

During winter, water from mountain streams is carried through pipes and sprayed into the cold air. It freezes and builds up in layers to form a tall ice structure.

As temperatures rise in spring, the ice melts slowly. The water can then be used for farming and other needs when natural streams may have less water.

Why Is the Shape Useful?

The tall cone shape exposes less surface area compared with the amount of ice stored. This helps the ice melt more slowly.

Ice stupas show how local communities use temperature and heat transfer for water conservation.

Class 7 Science Chapter 7 Summary Notes

Important Terms from Heat Transfer in Nature

Heat transfer: Movement of heat from a hotter region to a colder region.

Conduction: Heat transfer through neighbouring particles without their actual movement.

Conductor: A material that allows heat to pass easily.

Insulator: A material that does not allow heat to pass easily.

Convection: Heat transfer through the actual movement of particles in liquids or gases.

Convection current: Continuous circular movement formed by rising warm particles and sinking cool particles.

Sea breeze: Movement of cooler air from sea to land during the day.

Land breeze: Movement of cooler air from land to sea at night.

Radiation: Heat transfer that does not require a medium.

Water cycle: Continuous circulation of water between the Earth and atmosphere.

Evaporation: Change of liquid water into water vapour.

Transpiration: Release of water vapour from plant leaves.

Condensation: Change of water vapour into liquid droplets.

Precipitation: Falling of water from clouds as rain, snow or hail.

Infiltration: Seepage of surface water through soil and rocks.

Groundwater: Water stored below the Earth’s surface.

Aquifer: Underground layer that stores groundwater.

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