# Energy transfer by heating

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• Created by: Megan1404
• Created on: 27-02-16 19:22

Infrared radiation is energy transfer via electromagnetic waves.  These waves do not require particles to transfer energy thus they can travel through a vacuum, such as through space.

All objects emit infrared radiation.  The hotter an object is, the more infrared radiation it emits within a given time.

Dark and matt surfaces are the best absorbers of infrared radiation however they are also very good emitters of infrared radiation.  Light, shiny surfaces are good reflectors of it.

Therefore, a dark, matt surface will absorb heat energy at a faster rate than the same object that is light and shiny, yet it will also cool down more quickly because it is emitting heat energy at a faster rate.

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## Conduction

Conduction

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

When one end of a solid is heated, the tightly packed, vibrating particles will gain more kinetic energy so that they vibrate even more.  The particles will bump into neighbouring particles, passing along this energy and heating up the solid.

Metals are good conductors because they have many delocalised electrons that gain kinetic energy and move through the metal, colliding with the positive ions and transferring heat energy.

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## Convection

Convection

Convection occurs in fluids i.e liquids and gases.

When a fluid is heated the particles within it gain kinetic energy thus they move faster and the fluid expands, becoming less dense.  Hence the fluid rises.

The cooler fluid at the top cools the rising warm fluid, causing the particles to lose energy and the fluid to contract.  This makes it more dense and it falls to the bottom where the process is repeated and a convection current occurs.

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## Evaporation

Evaporation

Evaporation is when a liquid turns into a gas.  This happens when the liquid particles with the most kinetic energy break their bonds and escape from the surface of the liquid into the air.  Therefore, the average kinetic energy of the remaining liquid molecules is less thus the temperature of the liquid decreases.

Evaporation is a cooling process.

The rate of evaporation can be increased by:

• Increasing the surface area of the liquid
• Increasing the temperature of the liquid
• Creating a draught of air across the liquid's surface

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## Condensation

Condensation

Condensation is when a gas turns into a liquid.  Particles with the least amount of kinetic energy cannot move around as quickly so they come closer together and form bonds, condensing into liquid molecules.

The rate of condensation can be increased by:

• Increasing the surface area
• Reducing the surface temperature
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