Keeping Houses Warm Flashcards
Insulators are…
Materials that allow heat energy to spread through slowly
What is a conductor
A material that allows heat to spread through quickly eg metals
What are convection currents
Movement of hot air rising and cooler air taking its place.
Warm air becomes less dense and rises,the particles move quickly away from each other and expand, being replaced by denser air.
How do walls lose energy in the home
They absorb heat radiation
Energy is lost from SOURCE to…
SINK
Energy efficiency measures what
How good an appliance is at converting input energy into useful output energy
What does the amount of infrared given out/taken in depend on
How much infrared given out/taken in depends on ITS SURFACE
Transfer of heat energy by electromagnetic waves
How does conduction work
It is the transfer of heat energy through a substance from hotter to cooler without substance moving itself. Kinetic energy increases so particles vibrate. Energy transfers and passes along
What is radiation (on hot objects)
Transfer of heat energy by electromagnetic waves
Hot objects emit mainly infrared radiation which can pass through a vacuum so no material is needed for the transfer
What surface emits more radiation at room temperature
Dark matt
Heat can also move as infrared radiation (electromagnetic wave)
What surface reflects infrared
Shiny surfaces
Wont get as hot
Which surface is a better absorber of radiation
Dark matte
How does fibreglass loft insulation reduce heat loss in the home
Reduces convection and conduction by trapping layers of air between fibres
How do reflective foil on walls behind radiators reduce heat loss in the home
Reduces radiation by reflecting infrared heat energy into the room
For a television what is the input energy, useful energy and wasted energy
Electrical energy is input
Sound and light energy is output
Heat energy is wasted
How does cavity wall insulation reduce heat loss in the home
Reduces conduction and convection by trapping small pockets of air in the foam
How does double glazing reduce heat loss in the home
Reduces conduction and convection by trapping air between panes of glass
Amount of radiation given out depends on what (in a material)
How much infrared given out/taken in depends on it’s surface
Why are metals good conductors
Heat energy is also transferred by free electrons in a metal
They flow, collide with and transfer energy to other atoms increasing their kinetic energy so temperature rises
How do draught excluders reduce heat loss in the home
Reduces convection by keeping as much warm air inside as possible
What type of heat loss does insulation only prevent
Heat loss by conduction
How does convection cause heat loss
Because liquids and gases can easily flow they can transfer heat energy from hotter to cooler regions by their own movement. Cools overall temperature
Fast particles expand and become less dense so rise up to be replaces with denser liquid or gas
When heat is lost from a home what is the source and what is the sink
Home is source
Atmosphere is sink
Describe particle movement in a hotter object
Fast moving particles
In a solid they vibrate
In a liquid they flow past each other and move further apart
Why are refrigerators insulated
To reduce heat gain by conduction or convection
Why are curtains good insulators
Trap air between them and window helping to reduce heat energy loss by conduction
