How does a thermometer works?
Thermometer works on the principle of Thermal Expansion. All metals expand with increase in temperature & vice versa i.e. decrease in size with decrease in temperature.
In a common thermometer as shown in figure above, in the bottom small bulb, Mercury (a metal) is kept. It is worth mentioning that Mercury is unique in the sense that i. it is the only metal which is a liquid at room temperature & ii. It coefficient of thermal expansion is pretty high i.e. it the change in volume (or length of a fix area liquid column is very large).
This mercury rises up and down in the thermometer tube with increase & decrease in temperature. The tube is marked with temperature readings and can be read directly.
How do we define 10C temperature- Its simple. As a convention it is assumed that the pure water boils at 1000C & gets converted into ice at 00C.
The thermometer is kept in a boiling water. This gives us the mark of 1000C. Again, the thermometer is kept in an ice-water mixture. This gives us the 00C mark.
The intermediate length between these 2 marks is divided into 100 parts. Each partitions corresponds to 10C temp rise or decrease.
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