[Chemistry Class Notes] Kelvin Scale and Celsius Scale Pdf for Exam

What is the Kelvin Scale

When we discuss what is the meaning of kelvin or what is the kelvin temperature scale, we refer to it as the temperature scale which uses Kelvin or K for denoting the magnitude of temperature. It is the SI unit of temperature and is named after Sir William Thomson, an engineer and physicist. 

What is Kelvin Based On

In 1848, William Thomson, later known as Lord Kelvin, had written a paper “On an Absolute Thermometric Scale”, for needing a scale where infinite cold, now known as absolute zero, could be defined as the scale’s null point, and used degree Celsius for every unit increase.

He found that the absolute zero value on air thermometers was -273 °C. This was regarded as the absolute value, which is known as the Kelvin temperature scale. The value -273 of the Kelvin scale is referred to as the negative reciprocal of 0.00366. This is known as the gas expansion coefficient per one degree Celsius which is relative to the ice level.

What is Kelvin Used For

Let us discuss what is Kelvin temperature and what are its applications.

Kelvin temperature is used for measuring the temperature of the colours that are associated with the light sources. The colour temperature is dependent on the idea that the back body radiator emits light having temperature characteristics similar to the frequency distribution. These blackbodies appear reddish in colour below 4000 K temperature and bluish in colour above 7500 K. this concept of colour temperatures plays an essential role in image projection and photography in which the temperature of the colours equal to 5600 K is required for matching the emulsions of the daylight films. 

In the field of astronomy, the position and the stellar classification of the stars in the Hertzsprung – Russell diagram depend partially on their surface temperatures, which is also called as the effective temperature. An example of this is that the photosphere of the Sun has 5778 K as its effective temperature.

Kelvin temperature scale is also useful in electronics for measuring how noisy a circuit is relative to its noise temperature, or the ultimate noise levels. 

What is the Boiling Point of Water in Kelvin

The boiling point of water in Kelvin is 373 K.

What is the Freezing Point of Water in Kelvin

The freezing point of water in Kelvin is 273 K.

What is 1 Kelvin

Let us discuss what is the formula of Kelvin.

1K − 273.15 = -272.1°C

Now that we know what does kelvin mean, let us discuss about what is the Celsius scale and what is the formula to convert Celsius to Kelvin.

What is the Celsius Scale

The Celsius temperature is also known as the Centigrade scale and it was developed depending on the boiling point and the freezing point of water. Celsius is also an SI derived temperature unit. The Celsius scale is the most preferred scale for measuring temperatures in our day to day lives. 

Development of the Celsius Scale

In 1742, a Swedish astronomer and physicist Anders Celsius had developed a temperature scale, exactly opposite to the Celsius scale. According to this scale, the boiling point of water was 0 ℃ and the freezing point of water was 100 ℃. He also wrote a paper on the same in which he mentioned his observations from the experiments he conducted stating that the melting point of ice is unchanged even when there is variance in the pressure. He also calculated the variations in the boiling point of water with the changes in the atmospheric pressure.

From 1743, the Celsius temperature scale changed and the boiling of water was kept as 100 °C and the freezing point of water was kept as 0 °C at a pressure of 1 atm. This reversal of the Celsius temperature scale was proposed by Jean-Pierre Christin, a French physicist.

Conversion of Celsius to Kelvin

The formula to convert Celsius to Kelvin is given below.

0 degrees Celsius equals 273.15 Kelvins or 0°C + 273.15 = 273.15K

Hence, the formula is °C + 273.15 = K.