 # Kelvin Scale and Celsius Scale

## What is the Kelvin Scale?

The Kelvin scale is the temperature scale that uses the Kelvin to denote the magnitude of the temperature. The Kelvin is the SI base unit of temperature as suggested by the International System of Units (SI). This SI unit is named after the 1st Baron Kelvin – the Irish-Scottish physicist and engineer Sir William Thomson.

### Development of the Kelvin Scale

In the year 1848, via his paper named “On an Absolute Thermometric Scale”, The Irish-Scottish engineer and physicist William Thomson (later made the first Lord Kelvin) wrote about the need for a scale whereby “infinite cold” (commonly known today as absolute zero) would be clearly defined as the null point of the scale, and which used the degree Celsius for each of its unit increase.

Lord Kelvin determined that the value of absolute zero on the air thermometers of the time was equal to -273 °C. This absolute value is currently known as the Kelvin thermodynamic temperature scale. Kelvin’s value of ‘−273’ was the negative of the reciprocal value of 0.00366, which is the accepted gas expansion coefficient per degree Celsius relative to the ice level, attributing to the generally accepted value a remarkable consistency.

### Applications of the Kelvin Scale

The unit of temperature known as the Kelvin is used as a measure of the colour temperature associated with certain sources of light. The temperature of color is based on the idea that a black body radiator tends to emit light with its temperature characteristic of the frequency distribution. Black bodies are known to appear reddish at temperatures below 4000 K while the black bodies whose temperatures are above 7500 K tend to appear bluish. Colour temperature is a very important concept in the fields of photography and image projection, where a colour temperature that is approximately equal to 5600 K is needed to match the emulsions of “daylight” films.

The stellar classification of stars in the field of astronomy and their positions in the Hertzsprung – Russell diagram are partly dependent on their surface temperature (also referred to as the effective temperature). For example the Sun’s photosphere has an effective temperature of 5778 K.

The kelvin scale is also used in the field of electronics as a measure of how noisy a circuit is in relation to the ultimate noise level, that is, the noise temperature. The Johnson-Nyquist noise of discrete capacitors and resistors is a type of thermal noise that is derived from the Boltzmann constant. This can be used to calculate a circuit’s noise temperature using the Friis noise formulas.

## What is the Celsius Scale?

The celsius scale, sometimes referred to as the centigrade scale, is a temperature scale that was developed based on the freezing point and the boiling point of water. The celsius is an SI derived unit of temperature. It is the preferred scale that is used in order to measure temperatures in the day to day lives of human beings. The celsius scale is named after the Swedish mathematician, physicist, and astronomer Anders Celsius.

### Development of the Celsius Scale

In the year 1742, the Swedish physicist and astronomer Anders Celsius developed a temperature scale which was exactly the opposite of the scale now known as the celsius scale. In this scale, 0 denoted the boiling point of water and 100 denoted the freezing point of water. In the paper that he wrote titled “Observations of two constant degrees on a thermometer”, Anders Celsius outlined his observations from his experiments that demonstrated that the melting point of ice is basically unchanged by variances in pressure. As a function of the atmospheric pressure, Anders Celsius also calculated (with incredible accuracy) how the boiling point of water varied with variances in the atmospheric pressure.

From the year 1743 onwards, the Celsius scale was changed to be based on 0 °C for the value of the freezing point of water and 100 °C for the value of the boiling point of water when the pressure of the environment of the water was kept at 1 atm of pressure. The 1743 reversal of this temperature scale was proposed by the French physicist Jean-Pierre Christin.

## Frequently Asked Questions on Kelvin Scale and Celsius Scale

### Is negative Kelvin possible?

The particles stop moving at zero kelvin (minus 273 degrees Celsius), and all the disorder (or entropy) vanishes. So nothing on the Kelvin scale can be colder than absolute zero. This is also backed up by the third law of thermodynamics.

### What is the Kelvin scale used for?

Kelvin is also used in color temperature determination and is usually used in lighting. In a lighting application, Kelvin temperature reflects the color temperature that relates to the physical temperature of an object, such as blue, white, or bright red.

### What is the celsius scale based on?

Celsius is a temperature scale in which 0 degrees reflects the freezing point of water, and 100 degrees is the boiling point of water at the normal atmosphere, which is the mean barometric pressure at the mean sea level. The Swedish astronomer Andres Celsius established the temperature scale in 1742.