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objectives
objectives
Convection in a Liquid
Convection in a Liquid
- Liquids and gases are poor thermal conductors, but if they are free to circulate, they can carry thermal energy (heat) from one place to another very quickly.
- In the experiment on the right, the bottom of the beaker is being gently heated in one place only. As the water above the flame becomes warmer, it expands and becomes less dense.
- It rises upwards as cooler, denser water sinks and displaces it (pushes it out of the way). The result is a circulating stream, called a convection current.
- Where the water is heated, its particles (water molecules) gain energy and vibrate more rapidly As the particles circulate, they transfer energy to other parts of the beaker.
- Convection does not occur if the water is heated at the top rather than at the bottom. The warmer, less dense water stays at the top.
convection in a liquid video
convection in a liquid video
5.07---Convection.mp4Convection in Air
Convection in Air
- Convection can occur in gases as well as liquids. For example, warm air rises when it is displaced by cooler, denser air sinking around it.
- Heated by the Sun, warm air rises above the equator as it is displaced by cooler, denser air sinking to the north and south. The result is huge convection currents in the Earth’s atmosphere. These cause winds across all oceans and continents.
- Convection also causes the onshore and offshore breezes which sometimes blow at the coast during the summer
Using Convection in the Home
Using Convection in the Home
- Hot water system In the system above, hot water for the taps comes from a large storage tank.
- The water is heated by a coil of copper pipe: hot water from a boiler flows through this and is recirculated by a pump.
- In the tank, the heated water rises to the top by convection.
- In this way. a supply of hot water collects from the top down.
- The tank is insulated to reduce thermal energy losses by conduction and convection.
- Room Heating Warm air is rising above a convector heater or radiator carries thermal energy all around the room – though unfortunately, the coolest air is always around your feet.
- Refrigerator Cold air sinks below the freezer compartment. This sets up a circulating current of air which cools all the food in the refrigerator.
convection worksheet
convection worksheet
5.07---Convection.docxPage updated
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