ANOMALOUS EXPANSION OF WATER:


If we take some water at 00 C and start heating it, we find that it contracts in the temperature range from 0o C to 4o C. On heating it further above 4o C, it expand . Similarly, it water initially at a temperature above 4o C is cooled , it contracts till the temperature of water reaches 4o  C. On further cooling it below 4o C to 0o C, its expands. This unusual expansion of water on cooling it in the temperature range 4o C to 00 C is called anomalous expansion of water.


Explain the following……


1-Water pipes in colder countries often burst in winter.


   Ans-In winter nights, as the atmospheric temperature starts falling below 4 C, water in pipe lines expands and it exerts large pressure on the pipe , causing them to burst. Plants also die for the same reason as their capillaries burst when water expands below 4 C.

 

2-In winter , water tank (or ocean) starts freezing from the surface and not from the bottom.


Ans-In cold weather ( or winter) , when the atmospheric temperature starts falling below 00 C , water at the surface of a pond (or lake) initially at temperature above 40 C , begins to radiate  heat to the atmosphere, so the temperature of water near the surface starts falling . When temperature  of  water at the surface falls below 40 C, water contracts and its density increase and therefore, it sinks to the bottom.

 

3-Fishes survive in ponds even when the atmospheric temperature is below 00 C.


Ans-When the temperature of atmosphere falls below 00 C, water on the surface loses heat to the atmosphere and gradually freezes into ice, but water below the ice layer remains at 40 C. The  water layer just below the ice in contact with it will be at 00 C. Thus, temperature of water in contact with ice is 00 C, while the temperature of water layers below the ice gradually increases to 40 C. As a result, fish and other aquatic creatures remain alive in water of pond (or lake), though water on the surface has frozen into ice.

 

4-A hollow glass sphere which floats with its entire volume submerge in water at 40 C sinks when water is heated above 40 C.


Ans-When temperature of water at the surface falls below 40 C, water contracts and its density increases and therefore, it sinks to the bottom. This continuous till temperature of entire water reaches to 40 C results in expansion of water and so its density decreases. As  a result, water does not sink further, but it remains on the surface. This helps the glass sphere to float.  

 

5- A glass bottle completely filled with water and tightly closed at room temperature, is likely to burst when kept in the freezer of a refrigerator.


Ans-It is due to anomalous expansion of water. Mostly substance contract when cooled , but  water shows an unusual behaviour of expanding while it turns into solid. The expansion of water takes place as it is cooled from 40 C to 00 C .