CONVECTION
Convection: Liquid and gasses are poor conductor of heat. However, heat is transferred through fluids (liquid or gasses) easily by another method that is called Convection.A liquid or gas become lighter as it expend on heating. Hot liquid or gas transcends the warmed zone. The cooler liquid or gas from the surroundings fills the place which in turns is heated up. In this way, all the fluid is heated up. Therefore, transfer of heat through fluids takes place by the actual moment of heated molecules from hot to cold parts of fluid.
Transfer of heat by actual moment of molecules from hot place to a cold place is known as convection.
CONVECTION CURRENT IN AIR
Gases also expand on heating, thus convection current are easily set up due to the differences in the densities of air at various parts in the atmosphere.
Uses Of Convection Current
Convection current set up by electric, gas or coal heaters help to warm our homes and offices central heating systems in building work on the same principle by convection. Convection current occur on a large scale in nature. The day-to-day temperature changes in the atmosphere result from the circulation of warm or cold air that travels across the region. Land and sea breezes are also the examples of convection current.
LAND AND SEA BREEZES
Why does sea breeze blow during the day? Why does land breeze blow in the night?
Land and sea breezes are the result of convection. On a hot day, the temperature of land increases more quickly than the sea. it is because the land increases more quickly than the sea. it because the specific heat of the land is much smaller as compared to water. The air above land gets hot and rises up. Cold air from the sea begins to move towards the land that is called sea breeze.
At night, the land cools faster than the sea. Therefore, air above the land is warmer, rises up and the cooled air from the land begins to move towards the sea is called sea breeze.
GLIDING
A glider looks like a small aeroplane without engine. Glider pilots use upward movement of hot air current due to convection of heat. These rising current of hot air are called Thermals. Gliders ride over these thermals. The upward movement of air for a long period.
The birds stretch out their wings and circle in the thermals. The upward movement of air helps birds to climb up with it. Eagles, hawks and vultures are expert thermal climbers. After getting a free lift, birds are able to fly for a hours without flapping their wings. They glide from one thermal to another and thus travel through large distances and hardly need to flap their wings.
