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Convection

Heat and Temperature of Class 7

Heat and Temperature Convection

Heat transfer through the metal tea pot, when we put hot water in steel bucket ,the bucket get hot in these cases two solids are not contact with each other but a liquid flow make the solid hot. In the similar way when hot air make contact with glass window ,the glass window get hotter .In these examples the transfer of heat energy between a solid surface and the nearby movement of a liquid or gases takes place. This type of heat transfer is known as   convection. As liquid and gas motion goes more and more quickly the convective of heat transfer increases rapidly. In this process heat is transferred because a heated gas or liquid moves from one place to another.

natural convection

We can understand how hot air circulate the heat- Hot air is lighter in weight and cold air is heavy , when the air is hot it is lighter then heavy cold air try to takes position of hot air then a circulatory air motion takes place ,due to this circular motion the heat transfer from one place to another.

convection

Now we can understand how a room get hotter, when a wall inside the room get heat from outside air then inside cold air is replaced by hot air and circular motion between hot and cold air start from this process after some time the room is hotter then previous temperature

convection heating water

Air is the main fluid in our home to transfer heat by convection. Air is everywhere and it can come and go out from our house in many different places .

We know that the strong winds blow during summer season. In the summer season the earth gets hot due to the sun and the earth heats up the air near its surface. The hot air is lighter in weight then this hot air rises up. To fill the place of hot air, cold air from above rushes in with very high speed, due to this region strong windsforms.

From the give region in above example we can also understand why a sea breeze describes a wind that blows from the ocean inland towards land. This breeze occurs usual phenomenon   in the spring as well as in summer because of the greater temperature differences between the ocean and nearby land in imbalance between hot air and cold air, particularly in the afternoon when the land is at maximum heating from the sun.

imbalance between hot and cold air

In the day time , the sun heats up the ocean surface as well as the land but in different manner. Since water is a good absorber then the earth. Energy absorb by water is more than the earth. The land absorbs much of the sun’s energy as well.  However, water heats up more slowly than land heats up and so the air above the land become warmer compared to the air over the ocean.

The hot lighter air over the land rise in the day time. But over the water in the day time due to the colder air high pressure appears on surface of water. To maintain this , the air sink over the ocean from land . And due to this region the wind blow from the higher pressure zone over the water to lower pressure zone over the land causing the sea breeze. We can understand this if temperature difference the sea breeze strength differs.

And the processes reverse at night. The air over the see is now warmer with respect to the air over the land. When the Sun disappears the land loses heat quickly and the air above it cools quickly.  But the sea is able to hold onto this heat after the sun sets .Due to this temperature difference the low surface pressure to shift to over the ocean during the night and the high surface pressure to move over the land. Thus the wind blow from the land to the sea creating at night.

wind change in coastal area

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