Temperature scales
| English | Chinese | Pinyin |
|---|---|---|
| thermometer | 温度计 | wēn dù jì |
| thermocouple | 热电偶 | rè diàn ǒu |
| thermodynamic | 热力学 | rè lì xué |
| kelvin | 开尔文 | kāi'ěrwén |
| absolute zero | 绝对零度 | jué duì líng dù |
| Celsius | 摄氏度 | shè shì dù |
How a thermometer 温度计 works
- A thermometer needs something that changes with temperature.
- A liquid expands, a metal's resistance rises, a gas swells.
- Read that change and you read the temperature.
Temperature scale lab
Kelvin index = Celsius index + 2.73
Slide Celsius temperature and see the Kelvin scale shift by 273.
Kinds of thermometer
- Anything that changes repeatably with temperature works:
- expansion of a liquid, resistance of a metal, e.m.f. of a thermocouple 热电偶, volume of a gas.
A thermometer measures temperature on a defined scale
Select all the properties that can be used to measure temperature.
Any property that changes repeatably with temperature works. The fixed colour of the case does not.
The absolute scale
- The thermodynamic 热力学 (absolute) scale uses the kelvin 开尔文 (K) and depends on no single substance.
- Absolute zero 绝对零度 ($0\ \text{K}$) is the lowest possible temperature — least internal energy. Nothing is colder.
Absolute zero (0 K) is:
At 0 K a system has its least possible internal energy; nothing can be made colder.
Kelvin and Celsius 摄氏度
- $T/\text{K} = \theta/°\text{C} + 273.15$. So $0\ °\text{C} = 273\ \text{K}$.
- A kelvin and a Celsius degree are the same size, so a change of $1\ \text{K} = 1\ °\text{C}$.
- Always use kelvin in gas-law calculations.
Extrapolating the pressure-temperature line back to zero pressure gives absolute zero, about -273 degC
What is $27\ °\text{C}$ in kelvin?
$T/\text{K} = \theta/°\text{C} + 273 = 27 + 273 = 300\ \text{K}$.
A temperature rise of 1 K is the same as a rise of 1 °C.
The two scales have the same size of degree — only their zero points differ (by 273.15).
In gas-law calculations, the temperature must be in:
Gas laws use absolute temperature — kelvin. Using °C gives wrong answers.
You've got it
- a thermometer uses any property that changes repeatably with temperature
- absolute zero $= 0\ \text{K}$ is the lowest possible temperature
- $T/\text{K} = \theta/°\text{C} + 273$; use kelvin in gas laws