有野問關於物理的（２０分）

evaporate同boil 都可以產生到water stream, 你上述既情況應該係evaporate

以水為example

boil:所有water molecule 都得到足夠既kinetic energy 即係 由liquid convert to
gas

evaporate:部份water molecule 得到足夠既kinetic energy 然後 由 liquid convert to gas

佢係一個鐵餅，有電線插住，表面有ｄ燈圍住一個圓圈咁的，中間有一個地方好像就是噴水的地方

假如佢真係識噴水 咁佢不停將佢噴出黎既water evaporate 咁就可能會形成到你見既煙霧

boil 同 evaporate 既重要分別係:

boil:正常氣壓底下 要到達個沸點 先會開始

evaporate:唔駛到達沸點 只要夠kinetic energy就得,通常發生係表面既molecule

你有冇去過海洋公園? 佢有d似霧似水既氣體 會由d柱噴出黎 幫你降溫

果d都唔係熱啦

另一個情況就係改變氣壓 導致以上情況 如果氣壓高 咁物體既沸點就會下降
相反而言氣壓低 沸點上升

所以佢未夠100度就boil左 你就唔覺得太熱 因為佢比你想像中凍

2007-09-08 09:30:35 補充：
錯字請見諒

The heater heats the upper part of the water only.

Since water is a poor conductor of heat, heat is transferred by convection only.

The principle of convection is simply

"heated part rises & not heated part sinks"

However, since the heater always at the upper part of the water,

the water being heated cannot rise up further nor sink

the lower part water cannot rise up (because they are not being heated)

So convection current cannot set up.

The heat therefore cannot transferred to the lower part of the water easily.

As a result, while the lower part of water is cold, the upper part of water almost boils.

water steam

水精氣掛。