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Answers
1) The process of evaporation is always accompanied by a cooling effect. For example, when a liquid evaporates from the skin, a cooling sensation results. The reason for this is that only the most energetic molecules of liquid are lost by evaporation, so that the average energy of the remaining molecules decreases; the surface temperature, which is a measure of this average energy, decreases also.
OR, Evaporation causes cooling because the process requires heat energy. The energy is taken away by the molecules when they convert from liquid into gas, and this causes cooling on the original surface.
2) When a solid is heated, its atoms vibrate faster about their fixed points. The intermolecular force of attraction between the molecules (inter-particles) of a solid is very strong. The relative increase in the size of solids when heated is therefore small. Hence, solids expands the least.
3) Metal railway tracks have small gaps so that when the sun heats them, the tracks expand into these gaps and don’t buckle. If this is not fone, the rails would expand and bend when they will get heated, causing rail accidents prominent.
4) Electric transmission lines like telegraph and telephone wires are fixed between the electric poles but are kept loose. This is done to prevent them from breaking due to tightness, when they will start contracting in winter.
5) It is commonly observed that when hot boiling water is poured in a thick glass tumbler, it cracks. The reason for cracking is that glass is a bad conductor of heat. Thus, the inner surface of the tumbler expands more than the outer surface. Due to this uneven expansion, a strain builds up in the glass. It is this strain which cracks the glass.
6) We know that liquids does not have any definite length or area. Gases also does not have any definite length and area. They have something called volume (note : gases does not have any definite volume but of course all gases have some volume). Liquids and gases show only cubical expansion, but no linear and superficial expansion because they do not have a definite shape. Different gases have the same rate of expansion for the same rise in temperature, as compared to solids and liquids which show different rates of expansion for the same rise in temperature.
7) A little space is left in medicine bottles. If the bottles are fully filled then it may blast due to excessive pressure formed by increased kinetic movement or temperature. Kinetic movement increases due to shaking of medicine bottle(as on shaking, the molecules of the liquid strike with each other more randomly & will increase kinetic energy).
MUST TO NOTE : Considerable space is left in medicine bottles to allow the liquid content to expand when they are sent from cold to hot countries.
Explanation:
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