🔬 Chapter 7 — Heat Transfer in Nature
Class 7 Science | Curiosity | EduGrown Notes
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🌡️ Heat Transfer in Nature — Conduction, Convection, Radiation!
🔗 Conduction — Heat Through Solids
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🔗Conduction = transfer of heat from hotter part to cooler part of an object — particles vibrate but don't move!
🍳This is why metal cooking utensils get hot when placed on a flame — heat conducts along the metal
✅Good Conductors: Metals (iron, copper, aluminium) — allow heat to pass through easily
❌Poor Conductors (Insulators): Wood, glass, plastic, rubber, air, clay, porcelain — block heat flow
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🔥 Heat conducts along metal strip — pin nearest to heat falls first!
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🍵 Tea stays hot in clay cups — clay is a poor conductor!
💡 Everyday Examples of Conduction
🍳 Metal pan gets hot on stove → conduction through metal
🧣 Woollen clothes keep us warm → wool traps air, a poor conductor
🏠 Double blanket better than one thick blanket → air trapped between is a poor conductor
🍵 Clay/porcelain cups keep tea hot longer → clay is a poor conductor, heat stays inside!
🧣 Woollen clothes keep us warm → wool traps air, a poor conductor
🏠 Double blanket better than one thick blanket → air trapped between is a poor conductor
🍵 Clay/porcelain cups keep tea hot longer → clay is a poor conductor, heat stays inside!
🌀 Convection — Heat Through Fluids
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🌀Convection = transfer of heat through liquids and gases — particles MOVE, carrying heat with them!
⬆️Hot fluid becomes less dense → rises up | Cool fluid is denser → sinks down → creates convection currents!
💨This is why smoke rises — hot air expands, becomes less dense, rises upward
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💨 Convection currents — hot air rises, cool air sinks!
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🌊 Convection in liquids — heat moves with the fluid particles
🌊 Examples of Convection
🌬️Land and sea breezes — hot land heats air → rises → cool sea air replaces it
🌩️Weather patterns, monsoon winds
🍲Boiling water — hot water rises, cold sinks (convection currents)
🌋Lava movements inside Earth
☀️ Radiation — Heat Without Any Medium
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☀️Radiation = transfer of heat through electromagnetic waves — does NOT need any medium (can travel through vacuum!)
🌍The Sun's heat reaches Earth through radiation — 150 million km through empty space!
⬛Dark/black surfaces absorb radiation better (heat up faster) | White/light surfaces reflect radiation (stay cooler)
🔥We feel warmth when sitting near a campfire → heat travels through air by radiation
📊 Comparing All Three Methods
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| Property | 🔗 Conduction | 🌀 Convection | ☀️ Radiation |
|---|---|---|---|
| Medium needed? | Yes (solid) | Yes (liquid/gas) | No! Works in vacuum |
| Particle movement? | No — only vibrate | Yes — particles move | No — energy waves travel |
| Speed | Slow | Medium | Fastest (speed of light!) |
| Example | Metal rod heating up | Water boiling, sea breeze | Sun's heat reaching Earth |
⭐ Quick Summary
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📝 Key Points
🔗Conduction: heat through solids, particles vibrate don't move, metals = good conductors
🌀Convection: heat through liquids/gases, particles move and carry heat, creates currents
☀️Radiation: heat through electromagnetic waves, no medium needed, Sun heats Earth this way
⬛Dark surfaces absorb radiation (heat faster) | White surfaces reflect (stay cooler)