iGCSE Physics Section D

Energy transfers

Energy is conserved
Types of energy: thermal, light, electrical, sound, KE, chemical, nuclear, GPE, elastic potential energy.
Sankey diagrams show energy transfers.
total energy input=total energy output

efficiency = useful energy output / total energy input(http://www.bbc.co.uk/schools/gcsebitesize/science/images/14_1_efficiency.gif)

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Thermal energy

Thermal conduction: the transfer of heat through a substance without it moving.
   E.g. If one end of a copper rod had wax on it and you heated the other end, the rod would heat up and conduct the heat, making the wax melt.
Convection: the transfer of heat through liquids and gases (heat rising)
   E.g. Sea breezes
Radiation: the transfer of heat in the form of infrared waves.
  E.g. the sun warming the earth.

Reducing heat loss
By conduction:use a vacuum (e.g. double glazing)
                            use air (e.g. fibre glass insulation)
                            use water (e.g. wetsuits)
By convection:  use a vacuum
                            use trapped gas or liquid
By radiation:      use shiny surfaces

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Work and power

work, W = force, F x distance,d
 Work done in joules. Force in newtons. Distance in metres.
Doing work involves transferring energy. Energy and work are measured in joules. Energy is the ability to do work.

GPE = mass, m x gravitational field strength, g x height, h
KE = 1/2mv
power = work done / time

1 watt = 1 joule/second

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electricity generation

heat > boiler > high pressure steam > turbine > KE > generator > electrical energy

geothermal - getting heat from the earth's core
solar heating
nuclear fission
burning fossil fuels

GPE of water stored at height > KE falling down a hill > water driven turbine > generator > electrical energy

tidal power and wave energy
wind power
solar power

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