Different temperature scales have been used in the past. The most commonly known scales which scientists now tend to deal with are the Kelvin scale (K), the Celsius scale (^oC) and the Fahrenheit scale (^oF).

To design a temperature scale two fixed reference points have to be used. Once these points are set, we can divide the range into equal divisions in an appropriate interval. For example, in the Celsius scale, the freezing point is the lower fixed reference point and is given as 0 ^oC. The boiling point of water (100^oC) is taken as the upper fixed reference point. The difference between the two fixed points is divided into 100 equal divisions. Each division is called a degree.

Key Terms

• Absolute zero the temperature at which a substance has no thermal energy. It is unatainable temprature.