f.5phy evaporation concept 會考

Put a cup of water on the desk:

Q.1
Average K.E. of the particles of water remains unchanged.
(The average K.E. depends on the temperature of water only. The average K.E. of the particles remains unchanged in fixed temperature.)

Q.2
Total K.E. of the particles of water is decreased.
(The average K.E. of water remains unchanged, but the number of water particles is decreased as some water is evaporated.)

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Case 1:
Q.1
Average K.E. of the particles of water is increased.
(As the initial temperature of water is below the room temperature, water absorbs heat from the surroundings to rise its temperature. The average K.E. of water particles is increased as the increase in temperature of water.)

Q.2
Total K.E. of the particles of water is increased. (In most cases, but not in all cases)
(The average K.E. of water particles is increased, but the number of water particles is decreased due to evaporation. In most cases, the former factor outweighs the latter factor, and thus the total K.E. of water is increased. However, this is not true when the temperature of water is just slightly lower than the room temperature.)

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Case 2:
It is the case that to "put a cup of water on a desk" above.

Q.1
Average K.E. of the particles of water remains unchanged.

Q.2
Total K.E. of the particles of water is decreased.

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Case 3:

Q.1
Average K.E. of particles of water is decreased.
(As the initial temperature of water is above the room temperature, water releases heat to the surroundings to decrease its temperature. The average K.E. of water particles is decreased as the decrease in temperature of water.)

Q.2
Total K.E. of the particles of water is decreased.
(The average K.E. of water particles is decreased, but the number of water particles is also decreased due to evaporation.)
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http://hk.knowledge.yahoo.com/question/question?qid=7009012801724
呀sir話average ke 跌喎
因為個water surface escape the particles which carrys high KE so total + average KE 一同跌
比下意見