Physics Unit 1 GCSE Science

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  • Created on: 23-06-10 17:44

Heat Transfers

Heat Energy

  • Heat energy is transferred in three different methods: CONDUCTION, CONVECTION and RADIATION
  • Thermal (infrared) radiation is the tranfer of heat energy by Electromagnetic waves (EM Waves)
  • Conduction and Convection are the transfers of heat through particles.
  • Conduction takes place mostly in solid.
  • Convection currents take place in liquids and gases ONLY.
  • Whereas, Radiation takes place in all solids liquids and gases.
  • It can also travel through a vaccum.
  • The bigger the temperature difference between an object and its surroundings, the quicker the heat transfer
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Heat Transfers

(http://www.geography.hunter.cuny.edu/~tbw/wc.notes/2.heating.earth.surface/images/mechanisms.heat.transfer.jpg)

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Thermal Radiation

Thermal Radiation

  • Thermal/ infrared radiation is between Microwaves and Visible light in the electromagnetic spectrum (EM Spectrum)
  • It consists purely of EM waves
  • As I've said already.... The BIGGER the temperature DIFFERENCE, the FASTER the HEAT is TRANSFERRED.
  • The amount of heat radiated depends on its Surface area and colour
  • An object with a big surface area can transfer heat QUICKER due to more space - this means that it cools down and warms up quicker than a small substance.

* Dull Black surfaces ABSORB more heat radiation than Light Shiny surfaces

* Dull Black surfaces EMIT more heat radiation than Light Shiny surfaces

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Thermal Radiation

(http://www.gcsescience.com/Radiation-Black-White-Surface.gif)

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Conduction

Conduction

  • Conduction of heat takes place mainly in solids
  • It is where vibrating particles pass on their extra kinetic energy to neighbouring particles
  • This process continues throughout the solid and gradually some of the extra kinetic energy (heat) is passed all the way throughout the solid, causing a rise in the temperature
  • Metals are great Conductors...
  • ...This is because they have free electrons which move through the solid easily, passing on their energy much quicker than wood or plastic.

* If a spade has been left in the sun for a while, the metal part will always feel much hotter than the wooden handle, but it isn't. This is just because it conducts heat to your hands much quicker. IT IS NOT HOTTER. Remember that.

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Conduction

Step 3 - vibration is spread through the metal (http://www.bbc.co.uk/schools/gcsebitesize/science/images/18_3_conduction.gif)

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Convection

Convection

  • Convection currents take place in liquids and gases ONLY
  • Convection occurs when the more energetic particles move from a hotter region to a cooler region taking their heat energy with them
  • For EXAMPLE: In radiators (should be convectors) the cooler air of the room heats up and becomes less dense
  • Thus the warm air rises, going to a cooler region, pushing the cooler air beneath towards the radiator
  • The warm air itself cools and becomes more dense as it drops
  • The denser air sinks again....
  • AND IT CARRIES ON!
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Convection

(http://www.revisionworld.com/files/convection%20copy.jpg)

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