Heat Energy PDF

8/7/2019 Heat Energy PDF

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Heat and Temperature The temperature of an object tells ush o w it is Measured in degrees Celsius - C It is NOT the same as heat energyalthough the two quantities are related.e.g. a beaker of water at 60C is hotter

th an a bath of w ater at 40 C B U T thebath contains more joules of heatenergy


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Conduction cont ... Occurs by the particles hitting each otherand so energy is transferred. Can happen in solids, liquids and gases, Happens best in solids-particles veryclose together Conduction does not occur very quickly inliquids or gases


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Insulators/poor conductors Materials that conduct heat slowly or poorly arecalled insulators

Glass, wood, plastic and rubber are poorconductors (good insulators) Nearly all liquids including water are poorconductors (good insulators) Gases, including air are poor conductors,e.g.,wool feels warm because it traps a lot of air A fridge has insulation material round it to keep itcold - reduces amount of heat conducted toinside from the warmer room


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Convection cant ... The sun can cause large convectioncurrents - WINDS

During daytime the land warms up morethan the sea. The warm air rises over theland and cool air falls over the sea. So wefeel a sea breeze.

Rising convection currents can be uses byglider pilots to keep their planes in the airand by birds to stay aloft.


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Radiation Transfer of heat directly form the source tothe object by a wave, traveling as rays. H eat radiation is also know n as

All objects that are hotter than theirsurroundings give out heat as infra-redradiation

Heat transfer by radiation does not needparticles to occur and is the only way energycan be transferred across empty space


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Emittersobjects (give out) heat

D ifferent surfaces em it heat at differentspeeds A surfaces energy morequickly - it is a good radiator

A bright shiny or white surface is a poorradiator Marathon runners need to keep warm at theend of races, covering in shiny blankets

reduces rad iation and therefore heat loss.


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Absorbers Cooler objects absorb (take in) heat Substances absorb heat at different speeds Dull, black surfaces absorb heat quickly Bright, shiny surfaces absorb heat slowly.In hot countries, people wear bright whiteclothes and paint their houses white toreduce absorption of energy from the sun.

Petrol storage tanks sprayed silver to reflectsun's rays


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Heat Energy PDF