Conduction
- Hair dryers
- Hair dryers make use of fast flowing hot air to dry out hair quickly
- A motor pumps cool air through a heating element
- energy is transferred from heating element to fast flowing air via conduction
- Instant water heaters
- Instant water heaters employ a similar mechanism as hair dryers to heat water quickly.
- Cold water is passed through heating elements that transfer energy to water via conduction.
- Thermal wear
- Thermal wear contains porous materials like down feathers and microfibers that trap tiny pockets of air.
- As air is trapped in constrained space, there is no convection current.
- trapped air in thermal wear acts as an insulating layer and reduces body heat to surroundings via conduction.
- Double/Triple glazed windows
- air is a poor thermal conductor. thin layer of air trapped between 2 glass panes reduces energy transfer via conduction through window
- Energy transfer through window is further reduced with 3 glass panes and 2 layers of trapped air.
- Double or triple glazed windows help to keep interior of the home cool during summer and keep interior warm during winter.
Convection
- Electric kettles
- Heating elements are usually placed at bottom of electric kettles.
- when kettle is switched on, water around heating element heats up and expands.
- Heated water rises while cooler water at top part of the kettle sinks to replace heated water.
- convection current is set up - which allows water in kettle to be heated up more quickly and evenly.
- Hot air balloons.
- Burner at bottom of a hot air balloon heats up air above it.
- heated air expands and rises to the top of the balloon and displaces the cooler air.
- cooler air sinks to the bottom of the balloon, where it gets heated up. this movement of air sets up convection current.
- hot air has lower density than cool air. when sufficient air in the balloon is heated up, balloon rises.
- Sea Breeze
- During day, land heats up faster compared to sea water
- air above land heats up and rises.
- cooler air above sea rushes inland to replace space left by warm air
- sets up convection current, creating sea breeze.
- Land breeze
- during night, land cools down faster compared to seawater
- air above the sea heats up and rises.
- cooler air above the land rushes out towards sea to replace space left by warm air.
- this sets up a convection current, creating land breeze.
- refrigerator
- coolant is positioned at the top: cool air sinks.
Radiation
- Greenhouses
- suns radiation passes thru the glass and heats up the ground in greenhouse
- ground in the greenhouse becomes warm and re radiates infrared radiation with longer wavelengths.
- infrared radiation with longer wavelengths are unable to pass through the glass roof. it gets reflected and trapped in the greenhouse. this keeps greenhouse warm to support plant growth.
- Space Blanket
- Space blanket has shiny and smooth surface
- useful in emergency situations such as to help person who has fallen into very cold water, warm as it is a poor emitter of infrared radiation.
- can be used to wrap up houses to protect the houses against large scale bushfires as it is a poor absorber of infrared radiation. prevents the radiation from reaching and damaging the houses.
- Global warming
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earths atmosphere → is like a greenhouse.
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solar radiation that enters the atmosphere warms earths surface.
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surface then re radiates infrared radiation at longer wavelengths that are more easily absorbed by atmospheric greenhouse gasses.
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radiation absorbed will escape into outer space while remaining will have to go through more cycles of re absorption and re radiation before it escapes into space.
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amount of greenhouse gasses in the atmosphere has increased drastically due to human activities such as burning of fossil fuels.
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thus more energy is trapped by greenhouse gasses and temperature on earth increases, leading to global warming.