You have learnt that you need to choose two suitable points to calibrate a thermometer: lower fixed point and upper fixed point. Then divide the interval into equal division of a suitable unit. The two universal points to calibrate a temperature are the triple point of water (273.16 K, 611.73 Pa) and the absolute zero (0 K, 0 Pa). The triple point is the pressure and temperature at which water exists as a gas, liquid and solid simultaneously.

Key Terms

• The triple point is the pressure and temperature at which water exists as a gas, liquid and solid simultaneously.