Energy Transfer by Heating

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  • Created by: AlexxxF
  • Created on: 15-03-15 15:28

Infra red radiation

* Infra red waves are part of the electromagnetic spectrum

* Just beyond visible red light

* Detect infra red radiation with our skin- makes us feel warm.

* All objects emitt infra red radiation

* The hotter, the more infra red radiation is emitts.

* Can travel through a vaccuum- how we get enery from the sun. 

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Surfaces and radiation

* Dark, matt surfaces are good absorbers of infra red radiation.

* Dark, matt surfaces are good emitters of intra red radiation. 

* Light, shiney surfaces are good reflectors of infra red radiation. 

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States of matter

* Three states of matter- solid, liquid and gas

* Solid- particles vibrate about fixed positions so solid has fixed shape

* Liquid- particles are in contact with each other, can move at random, doesn't have fixed shape and can flow

* Gas- particles are far apart and move at random faster, doesn't have fixed shape and can flow

* Density of a gas is much less than a solid or a liquid

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* Conduction occurs mainly in solids- liquids and gases are poor conductors

* One end of a solid is heated, particles at that end gain kinetic energy and vibrate more. Energy passed to particles, all energy transferred.

* Metels heated, free electrons gain K.E and move through the metal, transferring energy.

* Materials such as wool and fibreclass are good insulators

* Non-metals are poor conductors as they don't have free electrons

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* Convection occurs in fluids- liquids and gases

* Convection is the circulation of fluids caused by heating it

* When fluid is heated, it expands, becomes less dense and rises. Warm fluid is replaced by cooler, denser fluids.

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* Evaportation is when liquid turns into gas

* Takes place because the most energetic liquid molecules escale from the liquid's surface and enter the air. Average K.E is less, so temperature decreases- causes cooling.

* Rate of evaportation is increased by

- increasing surface area

- increasing temperature

- creating a draught of air across the liquid's surface

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* Condensastion is when a gas turns into a liquid

* Takes place of cold surfaces such as windows and mirrors

* Rate of condensation is increased by

- increasing surface area

- reducing the surface temperature

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Energy Transfer by Design

* The greater the temperature difference between object and surroundings, the greater the rate energy is transferred

* Rate at which energy is transferred depends on

- materials object is in contact with

- the object's shape

- the object's surface area

* Maximise rate of energy- good conductors, painted dull black, air flow is maximised

* Minimise rate of energy- good insulators, white and shiney

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Specific heat capacity

* Specific heat capacity is the amount of energy required to raise the temperature of 1 kilogram of the substance by 1'C.

* Greater the S.H.C, the more energy needed for each degree temp. change

* The greater the mass of an object, the more slowly it;s temperature increases when heated. 

E=m x c x temp. change

E- energy transferred, J    c- specific heat capacity, J/kg 'C

m- mass, kg    temp. change, 'C

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Heating and insulating buildings

* U-Values tell us how much energy per second passes through difference materials. The lower the U-Value, the better the material is as an insulator. 

* Can be reduced by

- fibreglass loft insualtion to reduce energy transfer by conduction

- cavity wall insulation reduces energy transfer by convection

- double glazing to reduce energy transfer by conduction

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