| a. What is the role of anomalous behaviour of water in preserving aquatic life in regions of cold climate? |
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| → During winter, the temperature of the atmosphere can fall well below 0º C. As the temperature decreases, the water at the surfaces of lakes and ponds starts contracting. Hence, its density increases and it goes down to the bottom. This process continues till the temperature of all the water in a lake falls to 4º C. As the water at the surface starts cooling below 4ºC, due to anomalous behaviour of water, water starts expanding instead of contracting. Therefore, its density decreases and it remains at the surface of the lake. The temperature of the water at the surface of the lake continues to fall to 0ºC. Finally, the water at the surface is converted into ice but the water below the layer of ice remains at 4ºC. Ice is a bad conductor of heat. Thus, the layer of ice at the surface of the lake does not allow transfer of heat from water to the atmosphere. As the water below the layer of ice remains at 4ºC, fish and other aquatic animals and plants can survive in it.2 Marks |
| b. How can you relate the formation of water droplets on the outer surface of a bottle taken out of refrigerator with formation of dew? |
| → ‘At a given temperature, there is a limit on how much water vapour the given volume of air can hold. The lower the temperature, the lower is the capacity of air to hold water vapour. The temperature of a bottle kept in a refrigerator is lower than room temperature. When the bottle is taken out of the refrigerator, the temperature of the air surrounding the bottle is lowered. Therefore, the capacity of the air to hold water vapour becomes less. Hence, the excess of water vapour condenses to form water droplets (just like dew), on the outer surface of the bottle. 2 Marks |
| c. In cold regions in winter, the rocks crack due to anomalous expansion of water. |
| → Sometimes, water enters into crevices of the rocks. In cold regions, when the atmospheric temperature falls below 4º C, water starts expanding due to its anomalous behaviour. At 0º C, water is converted into ice and its volume increases. There is no room in the crevices for this expansion. As a result, tremendous pressure is exerted on the rocks leading to their cracking and breaking up into small pieces. 2 Marks |
This page was last modified on
30 July 2019 at 03:18