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  • Created on: 26-05-11 19:35
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Physics Revision ­ P1
Heat = A measurement of energy on an absolute scale. Measured in Joules. It is measured in joules
because it is a form of energy.
Temperature = A measurement of how hot or cold something is on a chosen scale. Can be seen on a
Specific Heat Capacity = How much energy is needed, in joules, to raise the temperature of 1kg of
the material by 1Degree Celsius. E = mcT ­ Energy = Mass * Specific Heat Capacity * Temperature Change
Specific Latent Heat = How much energy is needed to boil or melt 1 kg of that material. E = ml
------------- Energy = Mass * Specific Latent Heat
Conduction = Heat lost through solid materials, such as floors and walls
Radiation = Heat lost from outside surfaces, such as walls and windows
Convection = Heat is carried away by the movement of air, such as wind
Factors to consider when installing heating = Is it easy to install, How convenient is the fuel,
Payback Time = Installation Cost / Fuel Saving
Efficiency = Useful Energy Output / Total Energy Input
Infrared Radiation = Everything loses heat through infrared. It is a wave, similar to light, but with a
different wavelength, so it's invisible. Two properties of infrared = White or shiny surfaces reflect infrared,
White surfaces emit a lot less infrared than coloured ones.
Natural Convection = A low density fluid always floats on top of a high density fluid. When a fluid is
heated, it expands and so its density falls.
Conduction = In solids the particles are held together by forces between them, their heat energy
makes the particles vibrate.
Cavity Wall Insulation = Heat energy has to be conducted through the thin solid between holes. The
air in the holes is trapped, so it can't use convection to take the heat energy away.
Infrared and microwaves are similar. They are both waves carrying energy in the atmosphere. They
also have the same speed. The difference is that they have different frequencies.
Microwaves = They penetrate 1cm deep into the food. Heat energy is transferred to the water
particles, increasing their kinetic energy.
Infrared Cooking = Insulation to stop heat escaping. Hot black oven surface to emit the infrared
(because coloured materials emit more infrared than white materials. Heat energy flows into food via
conduction. The infrared waves transfer the energy.
Diffraction = Cause the signal to be weakened. The spreading out of waves as they pass through a
gap. Hence the reason why transmitters need to be high above the ground, so that buildings and other
obstacles don't get in the way of the signal.

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Analogue Signal = A continuously varying signal that can have any value.
Digital signal = It is either on (1) or off (0).
Multiplexing = More than one signal can be sent at one time.
Digital coding allows mobile phones to transfer information between people without error.
Optical Fibres = Thin glass strands, Infrared or visible light passes through them. Pulses of radiation
fed in at one end of the optical fibre passes all the way to the other end.…read more

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The ozone layer up in the atmosphere absorbs a lot of the suns UV light. CFCs damage the ozone
Sun block = The SPF of a sun block indicates how much UV light it can absorb. SPF 8 can allow you to
stay in the Sun eight times as long as you could if you didn't have the sun block on.
Climate change = The Earth absorbs light and infrared from the Sun, heating up the Earth.…read more


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