SI Unit of Temperature: Kelvin is the SI Unit of Temperature

Detailed Overview

Temperature, like any other physical quantity, is the measurement of a substance's or object's warmth or coolness in relation to a standard value. While it is used to convey hot and cold situations, the temperature is usually measured via a thermometer labeled in multiple temperature scales, the most common of which are Celsius and Fahrenheit. 

Temperature is a physical measure that quantifies our feelings of hotness and coolness. A thermometer is used to measure temperatures. Thermometers are calibrated on a variety of temperature scales that various reference points and thermometric substances have traditionally defined. The most prevalent scales are the Celsius scale (previously known as centigrade), the Fahrenheit scale (°F), and the Kelvin scale (K), with the latter being used mostly for scientific reasons. The kelvin is one of the seven basic units of the International System of Units (SI). Temperature is significant in all natural scientific domains, including physics, chemistry, Earth science, astronomy, medicine, biology, ecology, material science, metallurgy, mechanical engineering, and geography, as well as most elements of daily life.

Important Highlights

The following table gives details about the si unit of temperature-

According to the International System of Units, the SI unit of temperature is Kelvin, which is denoted by the sign K. In the fields of science and engineering, the Kelvin scale is generally acknowledged or employed. However, in most parts of the globe, temperature is measured using the Celsius or Fahrenheit scale.

The kelvin, symbol K, is a temperature measuring unit. The Kelvin scale is an absolute scale in which 0 K represents absolute zero and a change in thermodynamic temperature T of 1 kelvin equates to a change in thermal energy kT of 1.3806491023 J. In the 2019 redefinition of the SI base units, the Boltzmann constant k = 1.3806491023 JK1 was precisely specified, resulting in the triple point of water being 273.160.0001 K. In the International System of Units (SI), the kelvin is the basic unit of temperature, along with its prefixed versions. It is named after Belfast-born engineer and scientist William Thomson, 1st Baron Kelvin (1824-1907), who studied at the University of Glasgow. Historically, the Kelvin scale was derived from the Celsius scale, with 273.15 K equaling 0 °C (the approximate melting point of ice) and a change of one kelvin equaling a change of one degree Celsius. Although this relationship is still valid, the Celsius, Fahrenheit, and Rankine scales are now defined in terms of the Kelvin scale. The kelvin is the major unit of temperature in engineering and the physical sciences, whereas the Celsius scale remains the dominant scale in most nations outside of these professions. Outside of the physical sciences, the Fahrenheit scale predominates in the United States, with the Kelvin or Rankine scale used for absolute temperature.

How to Convert the SI Unit of Temperature into Fahrenheit?

The three most prevalent temperature scales are Celsius, Fahrenheit, and Kelvin. Each of the scales has a purpose; therefore, one will most likely come across them and need to convert between them. The conversion formula is provided below-

Read more about the Difference Between Celsius and Fahrenheit.

Other SI Units for Temperature

The following are the other si units of temperature-

1. Rankine
2. Newton
3. Romer
4. Réaumur
5. Delisle

Did you Know these Facts?

1. At this temperature, particles have, for all practical purposes, lost all of their motion energy.
2. During the manufacturing process, stainless steel is heated to about 1600 °C.
3. The lowest/coldest temperature on the temperature scale is referred to as "absolute zero" and is equivalent to 0 K or -273.15 °C. 

Practical Uses of Kelvin 

The following are some of the practical uses of the SI unit of temperature-

Color Temperature

Kelvin is frequently used to describe the color temperature of light sources. The rationale behind color temperature is that a black body radiator produces light with a frequency distribution typical of its temperature. Black bodies look reddish at temperatures below approximately 4000 K, and bluish at temperatures beyond about 7500 K. Color temperature is significant in picture projection and photography, where "daylight" film emulsions require a color temperature of around 5600 K. In astronomy, the stellar classification of stars and their position on the Hertzsprung-Russell diagram are dependent in part on their surface temperature, also known as their effective temperature. The Sun's photosphere, for example, has an effective temperature of 5778 K. In editing and setup menus, digital cameras and photography software frequently employ color temperature in K. The simple rule of thumb is that a higher color temperature generates more white and blue pictures. When the color temperature is reduced, the image becomes more dominated by reddish, "warmer" colors.

Kelvin as a Noise Temperature Unit

The kelvin is used in electronics to indicate how loud a circuit is with respect to an ultimate noise floor, i.e., the noise temperature. Johnson-Nyquist noise from discrete resistors and capacitors is a sort of thermal noise obtained from the Boltzmann constant that may be used to calculate the noise temperature of a circuit using the Friis noise formulae.

Points to Remember

1. The average kinetic energy of the object's molecules, which are heated and cause movement, is referred to as the temperature in terms of kinetic energy.
2. The Kelvin temperature unit in the SI is denoted by the letter "K."
3. The temperature in Fahrenheit will increase if the corresponding temperature in Celsius increases, and vice versa. This is because the two units are exactly proportional to each other.