✔ 最佳答案
1.What did he mean???
Mercury or alcohol expands on heating and contracts on cooling. But water expands, instead of contracts, when it is cooled from 4'C to 0'C.
2.Why water cannot use to make therometer?
Apart from the reason in Q1 above, water responds to change of temperature is not as fast as that of mercury. Also, water freezes at 0'C, this makes water unsuitable to be used in thermometers in cold contries where the temperature falls below 0'C in winter.
3. What did my teacher mean by 'Linearly'?
"Linearity" means "proportionality", for example, if a change of 1'C causes a rise of 1 cm of the liquid column, then a change of 2'C would lead to a change of 2 cm rise in the liquid column.
4. Why we use alcohol / mercury to make therometers?
The two liquids have melting points and boiling points suitable to be used in hot or cold countries. Mercury, being a metal, can respond quickly to a change of temperature. Also, the expansion is larger than other non-metal lliquids.
5. 1 atm pressure = 760mm Hg What does that mean???
The pressure, in N/m2, given by a Hg column of 760mm gives the same pressure at sea level as that given by the earth atmosphere.
Why we use mercury and measure its rise to test for atm. pressure instead of measuring the rise of water?
To measure atmospheric pressure using water column, the column needs to be 10.2 metres high. Such height is difficult to handle in a laboratory.
6.Why lower atm. pressure=less steam point?Why higher atm. pressure=more steam point?
The boiling point of water depends on the external atm pressure. A lower boiling point is resulted from a lower pressure. Simply speaking, the excape of water molecules into the air (i.e. boiling) becomes easily when a lower pressure acts on the water surface.
The reverse is also true for higher atm pressure, which makes excape of water molecules from the water surface difficult.
2009-09-08 20:45:07 補充：
7. A simple explanation is that water expands in volume when it forms ice because of crystalization. The increase of pressure makes the increase in volume more difficult. Hence, a lower temperature is needed for crystalization to take place.
