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The Common Unit Of Temperature and Si Unit Of Temperatre

We use Celsius scale of temperature for measuring temperatures in our everyday life. So, the common unit of measuring temperatures (like melting points, boiling points, etc.) is "degrees Celsius' which is written in short form as °C (read as degree C).The laboratory thermometers which we use for performing science experiments are all calibrated in 'degrees Celsius'. Even the clinical thermometer which we use for measuring human body temperature is calibrated on Celsius scale of temperature. The melting point of ice on Celsius scale of temperature is 0°C (zero degree Celsius). And the boiling point of water on Celsius scale is 100°C.
There is another scale of temperature called Kelvin scale of temperature which is used by the scientists mainly for research work. The SI unit of measuring temperature is Kelvin, which is denoted by the symbol K. Please note that the word 'degree' or its sign (°) is not written with the Kelvin scale temperatures. An advantage of the Kelvin scale of temperature is that all the temperatures on this scale are positive. The melting point of ice on Kelvin scale is 273 K. And the boiling point of water on Kelvin scale is 373 K.
We have just learnt that the melting point of ice on the Celsius scale is 0°C and on the Kelvin scale is 273 K. This means that a temperature of 0° on Celsius scale is equal to 273 on the Kelvin scale. So,
0°C = 273 K
The relation between Kelvin scale and Celsius scale of temperature can be written as :
Temp, on Kelvin scale = Temp, on Celsius scale + 273
This relation can be used to convert a Celsius temperature into Kelvin temperature or a Kelvin temperature into Celsius temperature. We should remember the above relation because it will be used to solve numerical problems as shown below.
Sample Problem 1. Convert the temperature of 25°C to the Kelvin scale.
Solution. We know that:
Temp, on Kelvin scale = Temp, on Celsius scale + 273
= 25 + 273
= 298 K
Thus, a temperature of 25°C on Celsius scale is equal to 298 K on the Kelvin scale.
Sample Problem 2. Convert the temperature of 300 K to the Celsius scale.
Solution. We know that:
Temp, on Kelvin scale = Temp, on Celsius scale + 273
So, Temp, on Celsius scale + 273
And,Temp, on Celsius scale = 300 - 273= 27°C
Thus, a temperature of 300 K on Kelvin scale is equal to 27°C on Celsius scale.
It is clear from the above discussion that:
(i) To convert a temperature on Celsius scale to the Kelvin scale, we have to add 273 to the Celsius temperature.
(ii) And to convert a temperature on Kelvin scale to the Celsius scale, we have to subtract 273 from the Kelvin temperature.