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P1B Fast Facts

- Heat is transferred by conduction by the particles vibrating and making those next to them vibrate.

- Conduction only occurs in solids as the particles cannot move around.

- Warm air is less dense and so rises.

- Conection is the movement of air from one place to another.

- Heat is transferred by radiation as a wave.

- Radiation can occur in all states of matter and a vacuum as it doesn't need particles.

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P1B Fast Facts

- Trapped air is a good insulator as the particles aren't close enough together for condcution to take place and the particles can't move so conection can't take place.

- A cavity wall is 2 layers of brick with a gap inbetween.

- Some cavity walls have foam in the gap, this is called cavity wall insulation.

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Payback time and energy efficiency

Payback time (years) = Cost of insulation
                                              annual saving 

Efficiency = Useful energy output / Total energy input x 100

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Sankey diagrams

total electrical energy is 100 j, 90 j is transferred as heat energy and 10 j transferred as light energy (http://www.bbc.co.uk/schools/gcsebitesize/science/images/14_1_efficiency.gif)

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Explain how design features reduce energy loss in

Fibre glass wool insulation is laid across the loft floor reduces conduction through the ceiling into the roof space.

Cavity wall insulation is two layers of bricks with a gap between them that redcues conduction.

Draught strips are strips of foram and plastic around doors and windows stop hot air going out - reducing convection.

Double glazing is two layers of glass with an air gap between to reduce conduction.

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