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  • Created on: 02-02-16 18:14

Energy Transfer

Infared Radiation

Infared radiation involves heat energy transfer by electromagnetic radiation, no particles of matter are involved.

All objects emit and absorb infared radiation, the hotter an object is, the more energy it radiates. The amount of infared radiation an object gives out or takes in, depends on its surface, shape and dimensions.

Dark, matt surfaces emit and absorb more infared radiation than light, shiny surfaces. Light shiny surfaces are good reflectors of radiation.

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Kinetic Theory

Kinetic Theory 

Kinetic theroy explains the states and properties of matter (solids, liquids and gases).

The particles in these three states constantly vibrate, but they vibrate more slowly when they are cooler, and faster when they are hotter, sometimes causing them to change their state.

                   Solid                                 Liquid                             Gas

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Energy transfer by heating

Energy transfer by Heating

Energy transfer by heating requires the movement of particles, when the particles collide with one another, the particles undergo changes that cause them to vibrate more or less, and transfer their energy.

The process of energy transfer can be carried out in one of four ways:

  • conduction
  • convection
  • evaporation
  • condensation
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Conduction occurs when particles within a material/matter are heated, causing them to vibrate more violently, their free elecrons that move freely around the material/matter carry the energy through it, causing it to heat up.

Insulators and Conductors

Insulators (such as cardboard) have very few or no free electrons to carry energy, so they do not conduct heat and/or electricity.

Conductors are the opposite, having lots of free electrons to carry the energy through the object.

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Convection is the movement of particles, that causes heat energy transfer.

Convection Currents

Convection only occurs in liquids and gases, and create convection currents:

  • Particles in the liquid/gas nearest the energy source gain energy and move faster, causing the substance to expand, and become less donse.
  • The now heated substance rises vertically, as it does so, it cools, becomes denser and then sinks.
  • The colder, denser substance moves into the space created (close to the heat source), and the cycle repeats. 
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Evaporation & Condensation


Evaporation occurs when a liquid is heated. Its particles vibrtate faster and more violently, then some of the particles that have enough energy, can escape from the surface of the liquid, and become a gas. This is called evaporation.


When a gas comes into contact with a cold surface, some of its energy that was being used to keep it in a gas form, is lost and transferred into the surface that it comes into contact with. When this happens, the gas' new lack of energy causes it to become a liquid. This is called condensation.

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Rate of Energy Transfer

Rate of Energy Transfer

The rate of energy transfer of a material depends on many factors:

  • its surface area and volume
  • what it is made from
  • the nature of the surface it comes into contact with
  • its temerature

The larger the temperature difference is between a material and its surroundings, the faster energy will be transferred.

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Specific heat capacity

Specific heat capacity

Every material has a different specific heat capacity.

The specific heat capacity of a material, is the amount of energy required to raise 1kg that material's temperature, by 1°C.

To work out the energy required, this equation is used:

                                           E θ

E = Energy transferred in Joules (J)

m = Mass (kg)

c = Specific heat capacity (J/kg)

θ = Temperature change (­°C)

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Energy Efficiency

An appliance's effiency refers to the proportion  of energy/power that is used usefully (for the appliance's purpose); the more efficient an appliance is, the more cost-effective it is.

To calculate efficiency, this equation is used:

Efficiency = (useful output ÷ total input) x 100%

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