# Relation between Fahrenheit and Celsius Scale

## Fahrenheit

The Fahrenheit scale, developed by the Polish–Danish physicist Daniel Gabriel Fahrenheit in 1724, is a scale of measurement used for temperature. The Fahrenheit scale makes use of the unit of degree Fahrenheit ( ˚ F). Fahrenheit developed this scale by accounting for the lower point in the scale (0 0 F) to be the freezing point of a solution he made using a mixture of water, ice and ammonium chloride. He set the other extreme limit by his rough calculations of the average human body temperature, which at that time was considered to be between 90 ˚ F and 96 ˚ F. This value is a minimum of 2.6 ˚F, less than the now accurate and modern value of the human body temperature, and this is because of a slight mis- definition of the Fahrenheit scale during its initial development. The middle value of the Fahrenheit scale, which was 32 0 F, was determined to be the temperature of ice water.

In recent days, the revised versions of the Fahrenheit scale have a 180 0 F difference between the two extreme ends; 32 0 F is fixed as the temperature where ice melts, and 212 0 F is fixed as the temperature where water boils, at sea level and under standard atmospheric pressure. The usage of the Fahrenheit scale has dwindled since it was first invented and predominantly used in the 18 th century, as most of the modern world has now shifted to the scale of Celsius for temperature measurement. However, Fahrenheit is primarily used in the USA and all its related regions.

## Celsius

Originally called the centigrade, the unit of Celsius is used in the Celsius scale of temperature measurement. It is denoted using the symbol 0 C. The Celsius scale was named so in 1948, in honour of the Swedish physicist Anders Celsius. Until 1743, the temperature scale of measurement had determined the boiling point of water to be 0 degrees and the freezing point of water to be 100 degrees. It was after the proposal by the French physicist Jean-Pierre Christin in 1743 that the scale was reversed. In recent days, the boiling temperature and freezing temperature of the water are considered to be 100 0 C and 0 0 C, respectively. Before 2019, both the unit Celsius and the Celsius scale were defined by the absolute zero and triple point temperatures of a substance and also associated the Kelvin scale to the Celsius scale.

Absolute zero (0 K and −273.15 °C) is the lowest possible achievable temperature of a substance, a temperature where all the molecules of the system are at a position of equilibrium and have minimum to negligible vibrations. Whereas the triple point of a substance is the temperature where all the three states of that substance exist in relative thermal equilibrium. The triple point of water was determined to be 273.16 K (0.01 °C). Kelvin is the scale of measurement of the temperature of thermodynamic systems. In 2019, the Kelvin scale was redefined in a way that its value was given in relation to the Boltzmann constant, which is a proportionality constant that relates the kinetic energy of particles with the thermodynamic temperatures. As a result, the triple point is now a measured value instead of previously being a defined value. However, the value dependence of the Kelvin and the Celsius with each other remains the same, i.e. 0 K = −273.15 °C.

## Relation between Fahrenheit and Celsius

The Fahrenheit scale and the Celsius scale are proportional to each other in that if the measured value of temperature goes up on one scale, the value will also correspondingly increase on the other scale. However, since they both have different manners in which the measured temperature values are defined, there will be differences. The freezing point of water is 0 0 C on the Celsius scale, while on the Fahrenheit scale, it is given as 32 0 F. Similarly, the boiling point of water is 100 0 C and 212 0 F on the Celsius and the Fahrenheit scale, respectively. For a value of temperature measured in the Fahrenheit scale to be converted into the Celsius scale, the following formula is used. C = 5/ 9 (F – 32) For a value of temperature measured in the Celsius scale to be converted into the Fahrenheit scale, the following formula is used. F = (9/ 5 × C) + 32

Where, in both cases

• C is the temperature in Celsius
• F is the temperature in Fahrenheit

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