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Explain the following: In winter, wate...

Explain the following:
In winter, water tank (or ocean) starts freezing from the surface and not the bottom.

Text Solution

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In winters, when temperature decreases, the surface of water in the tank contracts, becomes denser and sinks to the bottom. A circulation is thus set up until the entire water in the tank reaches its maximum density at `4^@C`.
When the temperature decreases further,the top layer expands and being less dense remains on the top till it freezes. Thus, water in a tank starts freezing from the top and not from the bottom.
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