Science · Class 7 · Chapter 7
Heat Transfer in Nature
Aim: Build a clear, working understanding of this chapter's key ideas, connected to real NCERT examples, worked problems, and everyday situations.
- Conduction — Heat transfer through particles, without them moving.
- Convection — Heat transfer by particles of liquid or gas moving.
- Radiation — Heat transfer needing no medium at all.
- Sea breeze / Land breeze — Cool air moving sea→land by day / land→sea by night.
- Water cycle — The continuous movement of water, Earth to sky and back.
- Infiltration — Surface water seeping through soil and rock.
- Groundwater — Water stored beneath the surface.
- Aquifer — An underground layer that stores groundwater.
Chapter 7 · Concept 1 of 8
Conduction
- Heat passes from the hotter part of an object to its colder part, particle by particle, without the particles themselves moving.
- Good conductors — Metals let heat pass through easily — that's why cooking utensils are metal.
- Poor conductors (insulators) — Wood, glass, and clay resist heat flow — that's why tea stays hot longer in a clay cup.
Chapter 7 · Concept 2 of 8
Convection
- When air or liquid is heated, it expands, becomes lighter, and rises — cooler fluid moves in to take its place, creating a current.
- In one line — Convection is heat transfer through the actual movement of particles in a liquid or gas — the main way heat moves in liquids and gases.
Chapter 7 · Concept 3 of 8
Land Breeze and Sea Breeze
- Daytime: sea breeze — Land heats faster than water. Warm air rises over the hot land, and cool air moves in from the sea.
- Night: land breeze — Land cools faster than water. Warm air now rises over the (relatively warmer) sea, and cool air moves from land toward it.
Chapter 7 · Concept 4 of 8
Radiation
- Heat transfers directly from a hot object — like fire or the Sun — to us, without needing any medium at all.
- Clothing and colour — Light-coloured clothes reflect heat (comfortable in summer); dark-coloured clothes absorb heat (comfortable in winter).
Chapter 7 · Concept 5 of 8
Conduction, Convection, and Radiation Together
- Conduction — Heat travels from the flame into the metal pan.
- Convection — Heat circulates through the water inside the pan.
- Radiation — You feel warmth in the air near the flame, directly.
Chapter 7 · Concept 6 of 8
The Water Cycle
- Evaporation & transpiration
- Water vapour rises, cools
- Condensation into clouds
- Precipitation: rain, snow, hail
Chapter 7 · Concept 7 of 8
How Fast Does Water Seep?
- Material | Seepage speed | Why
- Gravel — Fastest — Widest spaces between particles
- Sand — Medium — Smaller spaces than gravel
- Clay — Slowest — Tiny, tightly packed spaces
Chapter 7 · Concept 8 of 8
Groundwater and Aquifers
- Groundwater — Water that has seeped down and is stored in the pore spaces of sediments and openings in rocks.
- Aquifer — The underground layer of sediment or rock that stores groundwater — wells and borewells draw from it. Rainwater harvesting helps replenish it.
Quick Recap
Check Your Understanding
- 1Choose the correct option: a saucepan's handle (B) and base (A) — what is true of their materials? Also: which pins fall first on a heated metal strip? And: where's the best spot for a smoke detector?
- 2A shopkeeper puts a leaky tumbler of cold lassi inside a second tumbler. Will this keep the lassi cold longer? Explain.
- 3True or False, with reasons: (i) Heat transfer in solids happens by convection. (ii) Convection happens by particles actually moving. (iii) Clay lets water seep through faster than sand. (iv) Cool air moving from land to sea is called land breeze.