๐ฌ Chapter 7 โ Heat Transfer in Nature
Class 7 Science | Curiosity | EduGrown Notes
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๐ก๏ธ Heat Transfer in Nature โ Conduction, Convection, Radiation!
๐ Conduction โ Heat Through Solids
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๐Conduction = transfer of heat from hotter part to cooler part of an object โ particles vibrate but don't move!
๐ณThis is why metal cooking utensils get hot when placed on a flame โ heat conducts along the metal
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Good Conductors: Metals (iron, copper, aluminium) โ allow heat to pass through easily
โPoor Conductors (Insulators): Wood, glass, plastic, rubber, air, clay, porcelain โ block heat flow
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๐ฅ Heat conducts along metal strip โ pin nearest to heat falls first!
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๐ต Tea stays hot in clay cups โ clay is a poor conductor!
๐ก Everyday Examples of Conduction
๐ณ Metal pan gets hot on stove โ conduction through metal
๐งฃ Woollen clothes keep us warm โ wool traps air, a poor conductor
๐ Double blanket better than one thick blanket โ air trapped between is a poor conductor
๐ต Clay/porcelain cups keep tea hot longer โ clay is a poor conductor, heat stays inside!
๐งฃ Woollen clothes keep us warm โ wool traps air, a poor conductor
๐ Double blanket better than one thick blanket โ air trapped between is a poor conductor
๐ต Clay/porcelain cups keep tea hot longer โ clay is a poor conductor, heat stays inside!
๐ Convection โ Heat Through Fluids
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๐Convection = transfer of heat through liquids and gases โ particles MOVE, carrying heat with them!
โฌ๏ธHot fluid becomes less dense โ rises up | Cool fluid is denser โ sinks down โ creates convection currents!
๐จThis is why smoke rises โ hot air expands, becomes less dense, rises upward
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๐จ Convection currents โ hot air rises, cool air sinks!
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๐ Convection in liquids โ heat moves with the fluid particles
๐ Examples of Convection
๐ฌ๏ธLand and sea breezes โ hot land heats air โ rises โ cool sea air replaces it
๐ฉ๏ธWeather patterns, monsoon winds
๐ฒBoiling water โ hot water rises, cold sinks (convection currents)
๐Lava movements inside Earth
โ๏ธ Radiation โ Heat Without Any Medium
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โ๏ธRadiation = transfer of heat through electromagnetic waves โ does NOT need any medium (can travel through vacuum!)
๐The Sun's heat reaches Earth through radiation โ 150 million km through empty space!
โฌDark/black surfaces absorb radiation better (heat up faster) | White/light surfaces reflect radiation (stay cooler)
๐ฅWe feel warmth when sitting near a campfire โ heat travels through air by radiation
๐ Comparing All Three Methods
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| Property | ๐ Conduction | ๐ Convection | โ๏ธ Radiation |
|---|---|---|---|
| Medium needed? | Yes (solid) | Yes (liquid/gas) | No! Works in vacuum |
| Particle movement? | No โ only vibrate | Yes โ particles move | No โ energy waves travel |
| Speed | Slow | Medium | Fastest (speed of light!) |
| Example | Metal rod heating up | Water boiling, sea breeze | Sun's heat reaching Earth |
โญ Quick Summary
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๐ Key Points
๐Conduction: heat through solids, particles vibrate don't move, metals = good conductors
๐Convection: heat through liquids/gases, particles move and carry heat, creates currents
โ๏ธRadiation: heat through electromagnetic waves, no medium needed, Sun heats Earth this way
โฌDark surfaces absorb radiation (heat faster) | White surfaces reflect (stay cooler)