15. WHY does the surrounding become cold when snow starts melting?
When the snow around the surrounding melts, we experience a cold weather. This is due to the specific latent heat of fusion of ice.The specific latent heat of fusion of ice is relatively high at 336000 J/kg. This means that in order to melt one kilogram of ice, it requires 336000 Joules of heat. So to melt the whole mass of snow around our surrounding, it certainly needs a large amount of heat. Consequently, the heat available in the surrounding is absorbed to melt the snow.16. WHY does the steam at 100ºC causes severe burns than boiling water at the same temperature?
This is because of the high specific latent heat of vaporization of steam which is almost 2268000 J/kg. this means that 1kg of steam contains 2268000 joules of heat energy which is comparatively more than the boiling water at same temperature.
17. WHY are fishes able to float and sink in water?
Fishes have special organs called swim bladder precisely known as air sacs. To rise, the fishes allow the gases to fill in their swim bladder thereby increasing the volume. Since upthrust (upward force exerted by the liquid when an object is immersed in it) is directly proportional to the volume, the fishes are able to float. On the contrary, the removal of gases from air sacs will enable the fishes to go deep into the water.
18. WHY does a body weigh less in water?
Based on the Archimedes Principle, whenever an object is immersed either wholly or partially in the liquid, it experiences an upthrust which is equal to the weight of the fluid displaced. Due to this buoyant force (upthrust) exerted by the liquid on the object immersed into it, the weight appears to weigh less in water.
19. WHY do we feel cold when we take bath with cold water?
Heat is a physical quantity that flows when two bodies in contact have difference in temperature. It flows from a body having higher temperature to the body having lower temperature. Since cold water has lower temperature when compared to our normal body temperature (37.5 ºC / 98.6ºF), heat from our body is transferred to the water, thus making us feel cold. Also, water having high specific heat capacity, it needs a huge amount of heat to raise its temperature.
When two blankets are used, a layer of air is trapped between them. Since air is the poor conductor of heat, it doesn’t allow the heat from our body to escape to the surrounding, thus keeping us warm.
21. WHY are thermos flask able to keep the contents inside it very hot or cold for long time?
A thermos flask is constructed in such a way that it reduces the loss of heat through conduction, convection or radiation. It consists of a double-walled glass container inside with a vacuum in between the two walls to prevent the loss of heat by conduction and convection which requires a medium to transfer heat energy. The inner surfaces of the walls enclosing the vacuum are silvered so as to reduce the loss of heat by radiation. A plastic or wooden cork used on the top curtails the loss of heat by convection.“I have no special talents. I am only passionately curious”- Albert Einstein