Celsius and Kelvin scales

The Celsius and Kelvin scales are two common temperature scales. The Celsius scale indicates that 0 degrees is the freezing point of water, and 100 degrees is the boiling point of water at the standard atmosphere. Most countries in the world use the Celsius scale. The United States is one country that does not use the Celsius scale; it instead uses the Fahrenheit scale. The Kelvin scale, which uses the kelvin (K) as the temperature unit instead of the degree, adds 273.15 units to the Celsius scale. Therefore, the freezing point is 273.15 K and the boiling point is 373.15 K. Additionally, the lowest temperature on the Kelvin scale is 0 K. Both scales are commonly used in scientific applications.

Celsius Scale

The Celsius scale is the most commonly used temperature scale in the world. Furthermore, many scientific applications use the Celsius scale. It was developed by Anders Celsius, a Swedish astronomer, in 1742. Celsius performed experiments and set the boiling point of water at 0 degrees (or 0°C) and the freezing point of water at 100 degrees (or 100°C). After his death in 1744, the scale was inverted, thus making the freezing point 0 degrees and the boiling point 100 degrees. These are the freezing and boiling points on the Celsius scale in use today. Celsius wrote the paper “Observations of Two Persistent Degrees on a Thermometer,” in which he explained his experiments and demonstrated that latitude and atmospheric pressure affect the boiling point of water but do not affect the freezing point of water.

The Celsius scale was called centigrade for many years. Additionally, the temperature unit of the scale was called a centigrade degree. In an attempt to standardize units of measurement in 1948, however, the 9th General Conference on Weights and Measures (CGPM) officially changed centigrade to Celsius and centigrade degree to Celsius degree.

Around the same time that Celsius developed his scale, Daniel Gabriel Fahrenheit developed his own scale. In the early 1700s, Fahrenheit invented alcohol and mercury thermometers, and he later used his temperature scale on them. On the Fahrenheit scale, as on the Celsius scale, the freezing and boiling points of water are whole numbers. However, the freezing point is 32 degrees (or 32°F), and the boiling point is 212 degrees (or 212°F). Although Fahrenheit’s scale became the standard for some time, Celsius’s scale was considered the more precise scale. Today, the United States is one of the only countries in the world that continues to use the Fahrenheit scale. American scientists use the Celsius scale because they must share information with other scientists throughout the world.

Kelvin Scale

The Kelvin scale is another common temperature scale. British inventor and scientist William Thomson, also known as Lord Kelvin, developed the scale in 1848. The units of temperature on the Kelvin scale are kelvins rather than degrees. In written form, a capital “K” is used after the number instead of a degree symbol. In 1967, the 13th General Conference on Weights and Measures officially named kelvin and the symbol “K” as the temperature unit of the scale. An example of a temperature on the Kelvin scale is 280 K. The freezing point of water on the Kelvin scale is 273.15 K, and the boiling point of water is 373.15 K. This means that the Kelvin scale adds 273.15 units to the Celsius scale, and like the Celsius scale, includes 100 units between the freezing and boiling points.

Unlike the Celsius scale, the Kelvin scale does not have negative numbers. The lowest temperature on the scale is 0 K, also known as absolute zero. Absolute zero is the temperature at which a complete absence of heat energy occurs, and molecules stop moving. In the 1800s, scientists discovered a relationship between the volume and temperature of a gas. They theorized that at –273.15°C, the volume of a gas would become zero. Based on this theory, Kelvin developed his scale, using the same units as the Celsius scale. Therefore, while absolute zero is 0 K on the Kelvin scale, it is –273.15 degrees on the Celsius scale. Although absolute zero cannot be attained, scientists are able to come close to this temperature by using lasers to slow down particles.

Today, the Kelvin scale is used in scientific applications. Scientists find it useful because of its lack of negative numbers. Specifically, the Kelvin scale is used when recording the temperatures of liquid helium and liquid nitrogen, which have very low temperatures. Furthermore, the lack of negative numbers allows scientists to easily calculate the differences between temperatures.

Conversions

Conversions between the Celsius and Kelvin scales are easy. To convert from Celsius to Kelvin, simply add 273.15. For example, a temperature of 20°C is equal to a temperature of 293.15 K. To convert from Kelvin to Celsius, simply subtract 273.15. For example, a temperature of 323.15 K is equal to 50°C.

Conversions between the Celsius and Fahrenheit scales are more difficult. To convert from Celsius to Fahrenheit, multiply the Celsius temperature by 1.8, and then add 32. For example, a temperature of 5°C is equal to a temperature of 41°F. To convert from Fahrenheit to Celsius, subtract 32 from the Fahrenheit temperature and then divide by 1.8. For example, a temperature of 86°F is equal to 30°C.

Bibliography

“Metric System Temperature (Kelvin and Degree Celsius).” U.S. Metric Association. U.S. Metric Association (USMA), Inc. 2014. Web. 3 Dec. 2014. http://lamar.colostate.edu/~hillger/temps.htm

Zimmermann, Kim Ann. “Celsius: Facts, Formulas, & History.” LiveScience. LiveScience. 25 Sep. 2013. Web. 3 Dec. 2014. http://www.livescience.com/39959-celsius.html

Zimmermann, Kim Ann. “Kelvin Temperature Scale: Facts and History.” LiveScience. LiveScience. 27 Sep. 2013. Web. 3 Dec. 2014. http://www.livescience.com/39994-kelvin.html