# P1b: Keeping Homes Warm

The term insulation is used in the wider context of energy saving techniques in the home. This item develops ideas about the mechanisms of energy transfer by conduction, convection and radiation and the role they play in heat loss from homes. A poorly insulated home means that heat is being lost to the outside environment and more energy is needed to keep the home warm. Not only are energy resources being wasted but the home owner is also paying for energy that is lost to the outside environment. This item develops ideas about using energy efficiently and reducing energy losses from homes.

Explain why trapped air in a material is a very good insulator
Gases are particularly good insulators if you can stop them moving. This prevents them transferring heat by convection.
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What surface is infrared radiation reflected from?
Shiny surface
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What surface is infrared radiation absorbed by?
Dull/rough surface.
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Give two examples of using a black dull/rough surface to increase the amount of infrared radiation absorbed
Painting radiators black, and panels for solar water heating.
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Give an example of using a light-coloured smooth/shiny surface to increase the amount of infrared radiation reflected
Fridge shiny white, shiny surface on a patio heater to reflect heat downwards onto the patio, and put shiny foil behind radiators to reflect radiation back into the room rather than to heat up the walls.
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Name seven ways of preventing heat loss in the home.
Double glazing in windows, fibreglass, mineral or rock wool in loft insulation, foam insulation or fibre glass in cavity walls, curtains at windows, draught-proofing and fitting reflective foil in/on the walls
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How do you work out efficiency?
useful energy output (x100)/total energy input
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How is energy transferred by conduction? (H = hot, V = Vibrate C = charged, F = free, E = electrons, A = atoms, I = ions, KE = Kinetic Energy, M = metal)
E in M can leave their A&move about in M as FE.Parts of MA left behind are now CMI.I are packed closely together&V 2 cool.The Hter M,the more KE V have.This KE is transferred from H 2 cooler parts of M by FE.These move through M colliding with I.
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Why are liquids and gases fluids?
They can be made to flow.
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How is transferring thermal energy through radiation different to conduction and convection?
Unlike conduction and convection, which need particles, infrared radiation is a type of electromagnetic radiation that involves waves.
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When does convection occur?
onvection occurs when particles with a lot of heat energy in a liquid or gas move and take the place of particles with less heat energy. Heat energy is transferred from hot places to cooler places by convection.
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What do liquids and gases do when they are heated? Why?
Expand cuz the particles in liquids&gases move faster when they are heated than when they are cold.As a result,the particles take up more volume. This is because the gap between particles widens,while the particles themselves stay the same size
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Talk about the density and liquids and gases in hot areas compared to cold areas. Link this to convection.
The liquid/gas in hot areas is less dense than the liquid/gas in cold areas so it rises into the cold areas. The denser cold liquid or gas falls into the warm areas.In this way,convection currents that transfer heat from place to place are set up
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What type of energy is heat?
Thermal.
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How is heat transferred from one place to another?
By conduction.
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What is usually a good conductor of heat?
Metals
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What are usually poor conductors of heat?
Non-metals and gases,
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What is the name for a poor conductor of heat?
Insulator.
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How is thermal energy conducted?
From the hot end of an object to the cold end
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Why can we feel the heat of the sun?
Because radiation can even work through the vacuum of space.
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Which object will radiate heat energy faster? A thin object to a fat object?
Thin
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Where an object is hottest is where what?
The most heat is lost.
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How is heat energy transferred from homes?
Through the walls, floors, windows and roof.
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What areas of the house can cold air get in through?
gaps in doors and windows.
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Complete the sentence: _________ currents can transfer _____ energy in the _____ to the ______ ______
convection currents can transfer heat energy in the loft to the roof tiles.
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Heat energy leaves the house through walls, roofs and windows by what process?
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How does double glazing work?
These special windows have air or a vacuum between two panes of glass. Air is a poor conductor of heat, while a vacuum can only transfer heat energy by radiation.
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How does cavity wall insulation work?
This involves blowing insulating material into the gap between the brick and the inside wall, which reduces the heat loss by conduction. The material also prevents air circulating inside the cavity, therefore reducing heat loss by convection.
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What method of heat prevention works in the same way as cavity wall insulation?
Loft insulation.
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What do sankey diagrams summarise?
Sankey diagrams summarise all the energy transfers taking place in a process.
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The thicker the line/arrow on a sankey diagram means...
the greater the amount of energy involved.
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In which two terms can energy efficiency be expressed?
in ratio or percentage
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Complete the sentence: Energy can be _________ usefully, stored or dissipated. It cannot be ______ or _______
Energy can be transferred usefully, stored or dissipated. It cannot be created or destroyed.
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What happens to the rest of the energy in a sankey diagram, usually shown by a downwards arrow/line?
The rest is ‘wasted’ - it is eventually transferred to the surroundings, making them warmer. This ‘wasted’ energy eventually becomes so spread out that it becomes less useful.
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What is the efficiency of a device?
the proportion of the energy supplied that is transferred in useful ways.
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What will the efficiency of a device always be less than?
1
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How do you work out payback time?
payback time (years) = cost of installation (£) ÷ savings per year in fuel costs (£)
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What is the payback time of an energy-saving solution a measure of?
how cost-effective it is.
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What is the disadvantage of using energy-saving solutions?
They cost money to buy and install.
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When will the payback time be the shortest?
f the cost of installation is low compared to the savings made each year.
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## Other cards in this set

### Card 2

#### Front

What surface is infrared radiation reflected from?

Shiny surface

### Card 3

#### Front

What surface is infrared radiation absorbed by?

### Card 4

#### Front

Give two examples of using a black dull/rough surface to increase the amount of infrared radiation absorbed

### Card 5

#### Front

Give an example of using a light-coloured smooth/shiny surface to increase the amount of infrared radiation reflected