Heat Transfer in Nature
Conduction • Convection • Radiation • Clothing & Houses • Land/Sea Breeze • Water Cycle • Infiltration • Groundwater & Aquifers
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🧩20 Most-Important Words (with Simple Meanings in Hindi)
| Word | अर्थ (सरल हिन्दी में) |
|---|---|
| Heat | ऊष्मा — गरमी, जो वस्तुओं को गरम करती है। |
| Temperature | तापमान — किसी वस्तु/हवा की गरमी–ठंडी होने की माप। |
| Conduction | चालन — गरमी का ठोस में कणों के सहारे आगे बढ़ना (कण अपनी जगह रहते हैं)। |
| Conductor | सुचालक — वह पदार्थ जो ऊष्मा को आसानी से पास होने देता है (जैसे धातु)। |
| Insulator | कुचालक — वह पदार्थ जो ऊष्मा के प्रवाह को रोकता है (जैसे लकड़ी, काँच, वायु)। |
| Convection | संवहन — गरमी का द्रव/गैस में कणों की वास्तविक गति से फैलना (गरम ऊपर, ठंडा नीचे)। |
| Radiation | विकिरण — गरमी का बिना माध्यम के तरंगों द्वारा पहुँचना (सूर्य की ऊष्मा)। |
| Sea Breeze | समुद्री समीर — दिन में समुद्र से भूमि की ओर चलने वाली ठंडी हवा। |
| Land Breeze | स्थलीय समीर — रात में भूमि से समुद्र की ओर चलने वाली ठंडी हवा। |
| Evaporation | वाष्पीकरण — पानी का गर्म होकर भाप बनकर उड़ना। |
| Condensation | संघनन — भाप का ठंडा होकर पानी की छोटी बूंदों में बदलना। |
| Precipitation | वर्षण — बादलों से पानी/बर्फ़/ओलों का गिरना (बारिश)। |
| Transpiration | वाष्पोत्सर्जन — पौधों के पत्तों से पानी का भाप बनकर निकलना। |
| Water Cycle | जलचक्र — पृथ्वी पर पानी का निरंतर चक्र (वाष्पीकरण–संघनन–वर्षण–प्रवाह/अधःस्रवण)। |
| Infiltration | अधःस्रवण — सतह का पानी मिट्टी/चट्टानों के बीच से ज़मीन के भीतर जाना। |
| Groundwater | भूजल — जमीन के भीतर जमा हुआ पानी। |
| Aquifer | जलभंडार परत — भूमिगत परत जो पानी को संचित रखती है। |
| Good Conductor (of Heat) | अच्छा सुचालक — जो ऊष्मा जल्दी से पास करे (जैसे लोहा, तांबा, एल्युमिनियम)। |
| Poor Conductor (of Heat) | कुचालक — जो ऊष्मा को पास न होने दे (जैसे हवा, लकड़ी, प्लास्टिक, मिट्टी)। |
| Equator | भूमध्य रेखा — पृथ्वी के बीचोंबीच घिरी काल्पनिक रेखा; यहाँ जलवायु सामान्यतः गर्म होती है। |
📚Detailed Notes — Complete Coverage of the Chapter
7.1 Conduction of Heat (Heat flow in solids)
- Pin-on-metal experiment: Pins stuck with wax along a metal strip fall one-by-one from the heated end. Heat travels from hot end → cold end, melting wax near each pin.
- Definition: Conduction is heat transfer within a body from hotter part to colder part by particle-to-particle energy transfer. Particles do not leave their positions.
- Good conductors: Metals (copper, aluminium, iron) — that’s why cooking pans are metal.
- Poor conductors/Insulators: Wood, glass, clay, porcelain, air — reduce heat flow. Tea stays hot longer in clay/porcelain cups.
Woollen clothes keep us warm because air trapped in the fibres is a poor conductor. Two thin blankets (air gap) often feel warmer than one thick blanket.
House design: Hollow bricks trap air → cooler in summer, warmer in winter. In cold Himalayan regions, double wooden walls filled with mud/cow-dung reduce heat loss.
7.2 Convection (Heat flow by fluid motion)
- In gases (air): Air near a flame heats up, expands, becomes lighter, and rises. Paper-cup balance rises over a candle; smoke and a sun-warmed balloon demonstrate rising warm air.
- In liquids (water): Potassium permanganate streak moves up above the heat source and down along the sides — a convection current that spreads heat through the water.
7.2.1 Land & Sea Breeze (Daily wind reversal near coasts)
- Daytime (Sea Breeze): Land heats faster than sea → warm air over land rises → cooler air from sea flows toward land. Brings relief; coastal houses often have sea-facing windows.
- Night (Land Breeze): Land cools faster than sea → warm air over sea rises → cooler air from land flows out to sea. Hence, wind direction reverses at night.
7.3 Radiation (Heat transfer without a medium)
- Definition: Radiation carries heat as waves directly from hot objects (fire, Sun) to you — no material medium required.
- Examples: Feeling warmth near a fire; a hot pan cools by radiating heat to surroundings.
- Clothing colours: Light colours reflect more heat → better in summer; dark colours absorb more heat → warmer in winter.
7.3.1 All Three Together
- Heating water in a pan on a flame:
- Conduction: Flame → metal pan base
- Convection: Hot water rises, cool water descends
- Radiation: Heat felt around flame/pan
- Bukhari (traditional room heater): Uses all three processes to warm rooms and even cook on top.
7.4 Water Cycle (Powered by the Sun)
- States of water: Solid (ice, snow, glaciers), Liquid (rivers, lakes, oceans), Gas (water vapour in air).
- Steps:
- Evaporation: Sun’s heat turns surface water into vapour.
- Transpiration: Plants release water vapour.
- Condensation: Vapour cools → clouds.
- Precipitation: Rain/snow/hail returns water to Earth.
- Runoff & Infiltration: Water flows to water bodies or seeps underground.
- Importance: Redistributes and replenishes water; conserves total water on Earth. Clothes dry faster on sunny days due to faster evaporation.
7.4.1 Infiltration, Groundwater & Aquifers
- Bottle test (clay vs sand vs gravel): Water seeps fastest through gravel (larger open spaces), slower in sand, slowest in clay.
- Infiltration: Surface water moving down through soil/rock spaces.
- Groundwater: Water stored in pores and rock openings below ground.
- Aquifer: Underground layer that stores and yields groundwater; wells and bore wells tap this water.
- Conservation: Over-extraction + less vegetation/concrete increase depletion. Rainwater harvesting & recharge pits help. Ice Stupas in Ladakh store winter water as ice to melt in spring/summer for use.
At a Glance — Key Takeaways
- Conduction: Solids; particle-to-particle transfer; needs medium.
- Convection: Liquids & gases; actual motion of warm/cool parts; needs medium; explains land/sea breeze.
- Radiation: No medium; Sun → Earth; dark absorbs, light reflects.
- Design around heat: Clothing layers, house materials, hollow bricks.
- Water Cycle: Evaporation–Condensation–Precipitation–Runoff/Infiltration; Sun is the driver.
- Groundwater & Aquifers: Infiltration stores water underground; conserve via harvesting.
Safety: Candle/flame experiments must be done only under adult/teacher supervision.
Heat Transfer in Nature — Practice Pack
Conduction • Convection • Radiation • Land/Sea Breeze • Water Cycle • Infiltration • Groundwater
🔹1) One-Word Answer Questions (10)
- Q1. Heat transfer in solids by particle-to-particle transfer is called? Conduction
- Q2. A material that does not allow heat to pass easily? Insulator
- Q3. Heat reaching Earth from the Sun without any medium is? Radiation
- Q4. Heat transfer in liquids and gases due to actual motion of fluid is? Convection
- Q5. Daytime wind from sea towards land is called? Sea-breeze
- Q6. Night wind from land towards sea is called? Land-breeze
- Q7. Process by which surface water goes down through soil/rocks? Infiltration
- Q8. Water stored below ground in pore spaces is called? Groundwater
- Q9. Underground water-storing layer is known as? Aquifer
- Q10. Water vapour changing to tiny droplets to form clouds is? Condensation
✍️2) Fill in the Blanks (10)
| Question | Answer |
|---|---|
| 1. Metals are generally ______ conductors of heat. | good |
| 2. Woollen clothes keep us warm because they trap ______. | air |
| 3. In convection, warm fluid becomes ______ and rises. | lighter |
| 4. Land heats up ______ than sea during daytime. | faster |
| 5. Heat from the Sun reaches us by ______. | radiation |
| 6. The continuous movement of water on Earth is the ______. | water cycle |
| 7. Water going from liquid to vapour is called ______. | evaporation |
| 8. Soil with bigger spaces, like gravel, allows ______ infiltration. | faster |
| 9. Light-coloured clothes ______ heat and feel cooler in summer. | reflect |
| 10. Hollow bricks keep homes cooler as they trap ______. | air |
✅3) True/False with Explanation (10)
- 1. Heat transfer in solids is mainly by convection. — False
Explanation: In solids, particles cannot move freely; heat flows mainly by conduction. - 2. Radiation does not need any material medium. — True
Explanation: Sun’s heat reaches Earth through space by radiation. - 3. Land-breeze blows from sea to land at night. — False
Explanation: At night, cooler air moves from land to sea (land-breeze). - 4. Sea-breeze is felt during daytime. — True
Explanation: Land heats faster; cooler air from sea moves to land in the day. - 5. Dark colours reflect more heat than light colours. — False
Explanation: Dark absorbs more; light colours reflect more heat. - 6. Air is a poor conductor of heat. — True
Explanation: That’s why trapped air in clothing/blankets gives insulation. - 7. Infiltration is downward movement of water into the ground. — True
Explanation: Water seeps through soil/rock pores to become groundwater. - 8. Gravel allows slower infiltration than clay. — False
Explanation: Gravel has bigger connected spaces → faster infiltration. - 9. Convection currents form only in solids. — False
Explanation: Convection occurs in liquids and gases, not solids. - 10. Water cycle helps redistribute and replenish water on Earth. — True
Explanation: Evaporation–condensation–precipitation keep water moving and balanced.
🧠4) Very Short Answer Questions (2–3 lines each) — 10
- 1. Why do pins fall one by one in the heated metal-strip experiment?
Answer: Heat conducts from the hot end to the cooler end. Wax near the first pin melts earliest, so pin I falls first, then II, III, IV as heat reaches them. - 2. How do woollen clothes keep us warm?
Answer: Wool traps air in its fibres. Air is a poor conductor, so it slows heat loss from the body. - 3. Why does warm air rise in convection?
Answer: On heating, air expands, becomes less dense (lighter), and rises; cooler, denser air sinks to take its place. - 4. State one daily example of radiation.
Answer: Feeling the Sun’s warmth or feeling heat from a fire while standing at a distance. - 5. Why are light-coloured clothes better in summer?
Answer: Light colours reflect most of the heat radiation, keeping the body cooler. - 6. Define sea-breeze.
Answer: Daytime wind blowing from sea to land because land heats faster and air above it rises, drawing in cooler sea air. - 7. What is an aquifer?
Answer: An underground layer of rock/sediment that stores and yields groundwater through its pores/cracks. - 8. Mention two steps of the water cycle.
Answer: Evaporation (water → vapour) and condensation (vapour → droplets/clouds); also precipitation (rain/snow). - 9. Why do hollow bricks help in hot regions?
Answer: Air trapped in hollows acts as insulation, reducing heat transfer into the house. - 10. What is infiltration?
Answer: The process by which surface water seeps down through soil/rock to become groundwater.
📝5) Short Answer Questions (3–4 lines each) — 10
- 1. Differentiate conduction and convection with examples.
Answer: Conduction: Heat transfer within solids by particle-to-particle contact (e.g., spoon getting hot in a pan). Convection: Heat transfer in fluids by actual motion (e.g., water circulating when heated; warm air rising). - 2. Explain why sea-breeze occurs during daytime near coasts.
Answer: Land heats faster than sea; warm air over land rises. Cooler, denser air from sea flows toward land to fill the space, creating sea-breeze. - 3. Describe land-breeze at night.
Answer: Land cools faster than sea at night, so air over sea is warmer and rises. Cooler air from land moves seaward, forming land-breeze. - 4. How do houses use principles of heat transfer to improve comfort?
Answer: Hollow bricks/double walls trap air (insulation), reducing conduction. Orientation for natural breezes uses convection, and light-coloured exteriors reflect radiation. - 5. Why does gravel show faster infiltration than clay in the bottle test?
Answer: Gravel has larger, well-connected pore spaces allowing water to pass quickly; clay has tiny pores and slows the flow. - 6. Write the sequence of steps in the water cycle and its importance.
Answer: Evaporation/Transpiration → Condensation → Precipitation → Runoff/Infiltration. It redistributes water and helps recharge groundwater. - 7. How do we feel warmth near a fire even without touching it?
Answer: Through radiation: heat travels as waves directly from the fire to our body without needing a medium. - 8. Why do two thin blankets feel warmer than one thick blanket?
Answer: The air layer trapped between two blankets adds extra insulation, reducing heat loss more than a single thick layer. - 9. Explain how convection current forms in a beaker of heated water with dye.
Answer: Water at the bottom heats, expands, becomes lighter, and rises carrying the coloured streak; cooler water at sides sinks, creating a circulating current. - 10. Suggest two methods to conserve/recharge groundwater and why needed.
Answer: Build rainwater harvesting systems and recharge pits. Over-extraction and reduced natural infiltration deplete aquifers; recharge sustains supply.
Exam tip: Always name the process (Conduction/Convection/Radiation), state if a medium is needed, and give one everyday example.