Directions:In this section, there is one passage followed
by 6 statements. Go over the passage quickly. For questions 66-71, mark T (/for
True) if the statement agrees with the information given in the passage; F (for
False) if the statement contradicts with information given in the passage; NG
(for Not Given) if the information is not given in the passage. Questions 66-71 are based on the following
passage. 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. ______ On an extremely hot day, sweating to cool your body effectively will occur when the air is very hot and dry and carries no water at all.