Transfer Of Energy Flashcards
What is conduction?
Conduction is the transfer of energy within or between solids.
Heat causes the particles to vibrate so transmitting energy to particles close by.
Conduction requires direct contact between particles.
What is convection?
Convection is the transfer of energy when particles carry energy from one place to another.
E.g. When air is heated, the particles move faster and are further apart - it expands and becomes less dense so it rises. As it rises, the air cools and becomes more dense, so falls again and so creates a convection current.
Density = mass/ volume (kg/m3
Name some good conductors of heat.
Copper Aluminium Iron Any metal They conduct heat well because the particles are close together in a regular pattern. They also have free electrons which are free to move through the metal.
Name poor conductors of heat energy.
Poor conductors of heat energy are called insulators:
Solids where the particles are not close or in a regular pattern e.g. Wood, plastic and glass.
Liquids and gases because the particles are far apart and energy cannot be transferred easily between particles e.g. Water, air and vacuum
Name substances are good at convection?
Liquids e.g. Water, oil
Gases e.g air
What is infrared radiation?
Infrared radiation is the transfer of energy by electromagnetic waves.
If you put your hands close to a hot object but do not touch it the heat energy is being transferred by radiation.
All objetcs emit and absorb infrared radiation.
What is a thermogram?
A thermogram is a picture taken using a special camera which is sensitive to infrared radiation but not visible light.
The hotter something is the more infrared radiation is emitted in a given time.
What energy does the sun emit?
The sun emits infrared radiation.
Objects absorb the infrared radiation from the sun and warm up.
What factors increase the absorption of infrared radiation?
A dark, matt, rough surface is best at absorbing infrared radiation - solar panels need to be made out of this type of material.
A light coloured, shiny, smooth surface is worst at absorbing infrared radiation - it reflects it.
What is infrared radiation?
Infrared radiation is an electromagnetic wave.
It can travel through a vacuum (like light).
Insulation prevents heat loss through conduction and convection but not through radiation.
Why does double glazing reduce heat loss?
Double glazed windows are 2 panes of glass with air or argon or a vacuum between them.
Air and argon are good insulators - a vacuum is the best because there are no particles to conduct heat.
What is cavity wall insulation and how does it work?
Walls are made up of 2 layers of bricks with an air filled gap ‘cavity’ between them to reduce heat loss by conduction. However, heat can still be lost through convection and radiation.
Foam insulation injected into the cavities traps the air and reduces heat loss by convection by preventing convection currents developing.
New houses have blocks of foam with shiny surfaces on both sides to also reduce heat transfer through radiation.
Heat in in the house is reflected back to keep the house warm in winter.
Heat from the sun is reflected to keep the house cool in the winter.
Name some ways of preventing heat loss in houses.
- Keep windows and doors closed
- Double glazing
- Cavity wall insulation
- Loft insulation.
- Close curtains at night to reduce heat loss
- Foil behind radiators to reflect heat into the room.
- Draught strips around doors and windows to seal gaps.
How does loft insulation work?
If there is no insulation, warm air rises from the house and creates convection currents so warm air escapes through the roof. Loft insulation- rock wool or mineral wool traps air so convection currents cannot be created.
What is Energy efficiency?
Efficiency = useful energy output x 100%
———————————
Total energy output.
Can be represented by Sankey diagrams
