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www.GOALias.blogspot.comFig. 4.10 Transfer of heat by convection in airFig. 4.9 Convection of heat in waterand water from the sides moves down.This process continues till the wholewater gets heated. This mode of heattransfer is known as convection.How does the heat travel in air? Inwhich direction does the smoke go?The air near the heat source gets hotand rises. The air from the sides comesin to take its place. In this way the airgets heated. The following activityconfirms this idea.Activity 4.9Light a candle. Keep one hand above theflame and one hand on the side of theflame (Fig. 4.10). Do your hands feelequally hot? If not which hand feelshotter? And why?Be careful. Keep your hands at a safedistance from the flame so that theydo not get burnt.Notice that towards the top, the airgets heated by convection. Therefore, thehand above the flame feels hot. On thesides, however, there is no convectionand air does not feel as hot as atthe top.The people living in the coastal areasexperience an interesting phenomenon.During the day, the land gets heatedfaster than the water. The air over theland becomes hotter and rises up. Thecooler air from the sea rushes in towardsthe land to take its place. The warm airfrom the land moves towards the sea tocomplete the cycle. The air from the seais called the sea breeze. To receive thecooler sea breeze, the windows of thehouses in coastal areas are made to facethe sea. At night it is exactly the reverse(Fig. 4.11). The water cools down moreslowly than the land. So, the cool airfrom the land moves towards the sea.This is called the land breeze. Fig. 4.11shows this phenomenon.When we come out in the sun, wefeel warm. How does the heat from thesun reach us? It cannot reach us byconduction or convection as there is nomedium such as air in most part of the42SCIENCE