4.1.4 Calibrating a Thermometer

Calibrating a Thermometer

1. To calibrate a thermometer means to put the correct mark of reading at the correct place so that other temperature can be deduced from these marks. 
2. To do this, two extreme points are chosen to mark its scale and these points must be able to be reproduced accurately.
3. Usually, we take the steam point of pure water at 100°C and the ice point of water at 0°C.
   

   To calibrate a thermometer, the ice point of water is usually taken to be 0°C

   To calibrate a thermometer, the steam point is taken to be 100°C

4. After determining the position of the ice point and steam point, the temperature of an object can be determined by using the formula:

Example 3:

The figure above shows the length of the mercury thread of a thermometer at melting point and boiling point of water. What is the length of the mercury thread when the thermometer is dipped into a hot liquid of temperature 70°C?

Answer:
l₀ =4cm
l₁₀₀ =20cm
l_θ =?
T= 70 ^oC

The temperature of the water

Absolute zero and the Kelvin temperature scale

1. Absolute temperature is the temperature measured in Kelvin scale, which is a temperature reading made relative to absolute zero.
2. We can convert a temperature in °C to absolute temperature by adding 273 to the temperature.

3. Absolute zero is the temperature where thermal energy is at a minimum. It is 0 on the Kelvin scale and -273 on the Celsius scale.