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Overview         (For age - group : Above 16 )

Convection current in air or water can carry heat away from the hot source towards a cooler source. The sources could be separated by fraction of meter in case of air pockets in warm clothing or by kilometers in case of land sea breeze. This animated physics topic shows the mechanism of convection.

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Category : Science
Type : Animation

Convection currents :
The interactive e-learning animation
details case by case explanation
How land and sea breeze are formed?
Why the freezing unit is always fitted at the top of the refrigerator?
Why air conditioners are never installed near the floor of a room?
Why ventilators in the room are provided near the ceiling?
Why factories are fitted with chimneys?

Explanatory Notes contain :
What is convection?
Why convection current established in fluid?
Why water has a much higher heat capacity than that of land?

land breeze
sea breeze
In the night land is at lower temperature than sea hence a breeze blows in In the day land is at higher temperature than sea hence a breeze blows out
why ventilators are provided near the roof
freezing unit in a refrigerator always at top
Ventilator at the top of the room lets hot air out
Freezer is always at the top in a refrigerator
chimneys are provided in factories
air conditioner units are not installed near floor
Chimneys are provided in factories for letting out flue gases
Air conditioner units are not installed near the floor
Details of the animation/ movie /software

An important example of convection currents that can be interpreted in this manner is the creation of breezes over land masses next to large bodies of water. Thus, during the day the air above the water will be cooler than that over the land.

This creates a low pressure area over the land, relative to the high pressure area over the water, and subsequently one finds breezes blowing from the water to the land.

On the other hand, during the night water cools off more slowly than the land, and the air above the water is slightly warmer than over the land. This creates a low pressure area over the water relative to the high pressure area over the land, and breezes will blow from the land to the water. Places near the sea have pleasant and moderate climates because of the occurrence of land breezes and sea breezes.

Land breeze: the cold air blowing from the land towards the sea during night is called land breeze. Land being a good absorber is also a good radiator . Thus during the night , the land loses more heat by radiation. The specific heat capacity of land being lower than that of water, its temperatures in the early hours of the morning are lower than that of the sea. The air above the sea being warmer , expands, rises up and convection currents of cold air flow from the land towards the sea, forming land breezes.

Sea breezes:during day time , land becomes more heated than the sea . In the evening , air above the land, being more heated, expands, rises up and the colder air from above the sea surface blows towards the land to take its place. This sets up he convection currents which forms the sea breeze.

This would explain why:

  • The freezing unit is fitted to the top of the refrigerator
  • It is fallacious to install air conditioners near the floor
  • Ventilators in the room are provided near the ceiling
  • Factories are fitted with chimneys

More of this in the animation

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Q & A
Q1: How does formation of convection current happens duirng land breeze & sea breeze Narendra Singh 24/7/2012
Q2: why freezing heat is always fitted near the top in refrigerator v.saravanan 1/1/2011
Q3: how we know all these propertis of water? rameshnaik 22/8/2010
Q4: what causes formation of convection current in the air? amna 17/6/2010
Q5: describe an experiment to show convection current in air hana 24/8/2009
Q6: how is convection applied on the occurence of land breeze and sea breeze? phau 11/3/2009
Q7: why are convection current important in our atmosphere? kathy ward 27/5/2008
Ans: Air is a poor conductor of energy, so convection is a major process of energy movement in the Earth’s atmosphere. When the layer of air in contact with a hot surface warms by conduction, it acquires buoyancy due to lower density, and rises, taking with it the energy that it stores. This hot air called thermals rise upward from the warm surface. Warm air rises above cold air by convection. Clouds form when water vapor condenses and molecules cling to each other. If the thermal is vigorous enough, it will often form a cloud and sometimes grow into a thunderstorm. That is if the upward movement is violent, thunder clouds (cumulonimbus) are formed. Such convection processes results in the production of rain and snow, thunderstorms and hurricanes.
Q8: When you step into the bathroom in cold morning, the tiles feel cold than the bathroom floor mat. Is the floormat really warmer? Explain. Erin Joy Tinacba 6/3/2008
Ans: The floor mats are usually made of rubber, plastic or coir. Each of them is an insulating material that means the heat (or cold) from the bottom potion of the mat is not readily transferred to the top portion of the mat; hence the mat will feel warm as compared to the tile temperature. Actually it is warmer than the temperature of the tile. If you measure its temperature it will come out to be higher.
Q9: What is another name for a convection current in the atmosphere? Bailey Advincula 27/2/2008
Ans: Wind
Q10: what is the use of convection currents in a refrigerator and in air conditioning unit? francis molina 31/1/2008
Ans: In Refrigerator and in air conditioning unit, it is due to convection that warmer air rises and cooler air sinks, this causes a movement of air and leads to its even distribution throughout the space, this leads to cooler air cooling the bottom of the refrigerator unit and the lower heights of a room.
Q11: Whats the Difference between low pressure system and high pressure system? *cal* 26/9/2007
Ans: Air pressure. In high pressure system the pressure of air is high, that is air sinks towards ground, sinking very slowly flowing clockwise in northern hemisphere and vice versa. This results in a clear sky, cool and dry weather and no cloud formation. A low-pressure system (cyclonic) develops where relatively warm air ascends from the Earth's surface. Clouds rain and strong winds often occur in these regions. Rising air spirals inwards, in an anticlockwise direction in northern hemisphere.
Q12: whats the difference between Cold Front And Warm Front *cal* 26/9/2007
Ans: A front is the boundary between two air masses. Fronts are denoted by the type of air mass (cold or warm) replacing the other. A front is called a cold front if the cold air mass is replacing the warm air mass. There is change in wind direction and pressure as front passes. Thunderstorms and severe weather marks a cold front as compared to widespread, continuous precipitation of warm front that generally moves slower than a cold front. Warm fronts have gentler slopes than cold fronts do.
Q13: whats the difference between Continental air mass and maritime air mass *cal* 26/9/2007
Ans: Air mass is a large dome of air with typical characteristics of temperature and moisture, this is typified by when air rests over an area long enough to pick up the conditions of that area, air mass over desert will be dry and hot, Maritime air is a moist air mass, whereas continental air is relatively dry. There are four types of air mass. Tropical continental form over warm land and Polar continental over cold land. Tropical maritime form over warm seas and Polar maritime over cold seas.
Q14: Whats the Difference between Jet streams and Prevailing winds *cal* 26/9/2007
Ans: At the equator, air rises up due to heat, forming a low-pressure region in the doldrums. This air then subsides as it cools; it blows towards the equator as the trade winds, and towards the middle latitudes as the prevailing westerlies. They are prevailing winds of lower altitudes. With increasing elevation, the prevailing westerlies increase in speed and form thick narrow bands of high-speed winds of 125 knots at an altitude of 7 miles (11 km). These are called as Jet Streams.
Q15: whats the difference between Thermal And Chinook *cal* 26/9/2007
Ans: Chinook winds or Chinooks are the warm winds of the eastern Rocky Mountains, North America; they blow in from the west across the mountains. Chinooks can increase temperature dramatically, as high as 30 deg Celsius difference within 24 hours. Conversely, if chinook winds weaken, the cold air can move back in from the east, and the temperature will drop just as suddenly. A thermal is a column of hot air rising due to convection; this column rises in a spiral and has very strong currents.
Q16: What is water vapour and why is it important ?? janet 24/9/2007
Ans: Water vapor is a naturally occurring greenhouse gas, which causes about 40-70% of the greenhouse effect on Earth. It also controls the permittivity of the air and lightning production. Most of it is contained in the troposphere. The increased water vapor in atmosphere, in turn leads to an increase in the greenhouse effect. Water vapor contributes to greenhouse warming through a positive feedback but cloud formation increases reflection off clouds so less heat reaches earth producing a cooling.
Q17: How does a Bald Eagle soar on Thermal convection currents? diana arnold 7/8/2007
Ans: A thermal is a column of hot air rising due to convection; this column rises in a spiral and has so strong currents that even aircrafts avoid it. For an eagle, a thermal is like an elevator that carries the eagle effortlessly high into the sky. Eagles weigh only 10-14 pounds for their large 72 to 85 inches wings, even gently rising air pushes them up when their wings are spread. They soar in circles along with rising currents and glide from one thermal to another without flapping wings.
Q18: Why is a freezer always at the top of a refrigerator? Physicist 31/3/2007
Ans: In a convection cycle hot air rises and cool air falls, the freezer is at the top so that air cooled by it falls down the sections of a refrigerator and this type of design helps maintain a lower temperature at the top (for ice creams and ice cubes) as compared to that at the bottom (vegetable) section.
Q19: what is convection rai 30/3/2006
Ans: Convection results from the transfer of heat by currents within a fluid (from water to molten lava). It arises from temperature differences either within the fluid or between the fluid and its boundary. There are two types of convection forced and free convection (hot air rising from a surface) forced would be (boiling of water). There is always a density variation produced by temperature that produces convection.
Q20: What is the convection current in an air conditioned room? BOO BOO 13/3/2006
Ans: In an airconditioned room, the ACs are mounted at a height above the floor , the hot air rises and is cooled by the AC, the cooler air falls, this sets up a cycle. As we sit or sleep nearer to the floor we get the maximum benefit of cool air. Acs near the floor level do not cool as much as those high above the floor

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