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Thermal Energy Transfer
How is heat (thermal energy) transferred and what factors affect the rate at which heat is
Candidates should use their skills, knowledge and understanding of how science works:
· To evaluate ways in which heat is transferred in and out of bodies and ways in which the
rates of these transfers can be reduced.
Their skills, knowledge and understanding of how science works should be set in these
· Thermal (infra red) radiation is the transfer of energy by electromagnetic waves.
· All bodies emit and absorb thermal radiation.
· The hotter a body is the more energy it radiates.
· Dark, matt surfaces are good absorbers and good emitters of radiation.
· Light, shiny surfaces are poor absorbers and poor emitters of radiation.
· The transfer of energy by conduction and convection involves particles and how this
transfer takes place.
· Under similar conditions different materials transfer heat at different rates.
· The shape and dimensions of a body affect the rate at which it transfers heat.
· The bigger the temperature difference between a body and its surroundings, the faster the
rate at which heat is transferred.
"Many devices take in input energy in one form and transform it to output energy in
another form. They never transform all of the input energy to the output form we
want or transfer it all to the place we want. We need to know how efficient devices
are so that we can choose between them and try to improve them." Specification
We are all concerned about the effectiveness of machines in fulfilling their function because
of the energy cost in running them. One measure of this effectiveness is 'Energy efficiency'
When energy is transferred and or transformed only part of it may be usefully transferred/
transformed. The greater the percentage of energy that is usefully transformed in a device,
the more efficient the device is.
Both wasted energy and the energy which is usefully transferred / transformed are eventually
transferred to their surroundings which become warmer.
Energy becomes increasingly spread out and becomes increasingly more difficult to use for
further energy transformations.
This is known as ENTROPY
"We often use electrical devices because they transform electrical energy to whatever
form of energy we need at the flick of a switch. Electrical energy can be transferred
across large distances without the movement of appreciable amounts of mass."
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"Various energy sources can be used to generate the electricity we need. We must
carefully consider the advantages and disadvantages of using each source before
deciding which energy source(s) it would be best to use in any particular situation."
Uses and Hazards of EM Waves
What are the uses and hazards of the waves that form the electromagnetic
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Electromagnetic radiations are disturbances in an electric field. They travel as waves
and move energy from one place to another.…read more
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Infra red and visible light can be used to send signals along optical fibres and so
travel in curved paths.
Communication signals may be analogue (continuously varying) or digital (discrete
values only, generally on and off). Digital signals are less prone to interference than
analogue and can be easily processed by computers.…read more
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The Red shift of light from
distant stars is evidence that the Universe is expanding and moving apart.
Cosmic Background Radiation.
This shows that the temperature has cooled from the time of the Big Bang to reach a
stable temperature today. Only the Big Bang explains this cosmic background
radiation which is found everywhere in the Universe.
Helium Abundance. There is far more Helium in the Universe, than could be
produced by stars.…read more