1. Describe the process of convection of heat?
  2. Draw a neat labelled diagram of a thermos flask. How does it prevent transfer of heat by conduction, convection and radiation?
  3. How sea breeze and land breeze are set up in different paragraph and should be short? 

Sea Breeze is the mild to moderate wind blows from sea to land in the day.

Land being solid surface can easily absorb and release heat radiation. While sea being liquid heats up slowly and also loses this heat slowly. During the day time the sun heats up the land surface while the water body keeps on absorbing heat and is not hot yet. Land surface being hotter, hot air from land surface rises up creating a temporary low pressure zone which drags cool air from the sea to the land. Thus, we have the sea breeze.

Land Breeze is the mild to moderate wind blows from land to sea in the night.

As the day progresses and sun sets, the land loses heat quickly and the water body remains hot as it takes time to lose heat. During the night time, the land surface is cool as it loses its heat quickly. But the sea surface is still hotter as water bodies lose heat slowly. So, hot air from sea surface rises up and cool air from the land surface moves towards the sea. Thus, we have land breeze.

 

A thermos flux is a thermally insulated container that is used to hot water or other liquid like tea, milk etc., so, that the liquid remains hot for a longer time. The space between the inner and the outer wall of the flux is vacuum. Thus, heat cannot be conducted from the surrounding into the flux. So, hot liquid remains hot and cold liquid remains cold within a thermos flux.

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Convection is a mode of heat transfer by actual motion of matter. It is, therefore possible only in fluids. Convection can be natural or forced. In natural convection, gravity plays an important part. When a fluid is heated from below, the hot part expands and, therefore, becomes less dense. Because of buoyancy, it rises and the upper colder part replaces it. This again gets heated, rises up and is replaced by the colder part of the fluid. The process goes on. This mode of heat transfer is evidently different from conduction where energy transfer takes place locally due to intermolecular collisions. Convection involves bulk transport of different parts of the fluid. In a liquid, you can actually see it, for example, by colouring the liquid with potassium permaganate crystals at the bottom of the container.

In forced convection, material is forced to move by a mump or by some other physical means. Heat transfer in a liquid by brisk stirring or in air by a blower or a fan is example of forced convection

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