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  3. Heat loss by sweating depends on the fact that when a liquid evaporates, it

Heat loss by sweating depends on the fact that when a liquid evaporates, it

游客2024-08-19  32
问题     Heat loss by sweating depends on the fact that when a liquid evaporates, it absorbs an enormous quantity of heat from its surroundings. Therefore, when 1 ml. of sweat evaporate, a great deal of heat is absorbed from the surface of the body in contact with it. This heat transfer occurs even if the environment is hotter than the body.
    Two factors affect the rate of evaporation of sweat, and therefore the effectiveness of sweating as a method of cooling the body. The first is the amount of movement of air surrounding the body. The second is the amount of water vapor in the air that surrounds the body.
    When air moves over the surface of water, the amount of evaporation is greatly increased. For this reason, sweat evaporates very rapidly on windy days, and the rate of heat loss by sweating is much more than on a still day. This accounts for the fact that hot still days are much less comfortable than hot windy days. In contrast, the sweat evaporates very rapidly on hot windy days, and cools the body quickly and effectively.
    The second factor is the amount of water vapor in the air--the humidity. When air is carrying the maximum amount of water vapor that it can hold, it is said to be 100% saturated with water vapor. The relative humidity of the air is said to be 100%. Under these conditions the air cannot carry any water, so no water can evaporate. When the relative humidity is high, therefore, sweat cannot evaporate. Instead, it forms large drops and runs off your skin without cooling you.
    When the air is very dry and carries no water at all, the relative humidity is said to be 0%. It is obvious that under these conditions, evaporation will be much more rapid. Therefore, sweating will be much more effective as a method of losing heat from the body. On a hot dry day, sweat evaporates as soon as it is formed, and you feel reasonably cool even though the temperature of your environment is very high. [br] ______ People have good reasons to feel cool on a hot dry day because of quick evaporation.
选项 A、T
B、F
C、NG
答案 B
解析
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