Kelvin to Triple point of water
K
TPW
Conversion History
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Quick Reference Table (Kelvin to Triple point of water)
| Kelvin (K) | Triple point of water (TPW) |
|---|---|
| 0 | 0 |
| 255 | 0.9335188155 |
| 273 | 0.9994142613 |
| 293 | 1.0726314233 |
| 310 | 1.134866011 |
| 373 | 1.3655000713 |
About Kelvin (K)
The kelvin (K) is the SI base unit of thermodynamic temperature. Unlike Celsius and Fahrenheit it has no degree symbol — temperatures are written "310 K", not "310°K". Kelvin is an absolute scale: 0 K is absolute zero, the theoretical lower bound of temperature where molecular motion effectively ceases. Since the 2019 SI redefinition, the kelvin is fixed by the Boltzmann constant (k = 1.380649 × 10⁻²³ J/K). Kelvin and Celsius share the same degree size — a change of 1 K equals a change of 1°C — making conversion straightforward: K = °C + 273.15. Kelvin is used in physics, chemistry, astronomy, and engineering thermodynamics.
The surface of the Sun is approximately 5,778 K. Liquid nitrogen boils at 77 K (−196°C). The cosmic microwave background temperature is 2.725 K.
Etymology: Named after William Thomson, 1st Baron Kelvin (1824–1907), the Irish-Scottish mathematical physicist who first proposed an absolute temperature scale in 1848. He was ennobled as Baron Kelvin of Largs in 1892, after the River Kelvin in Glasgow near where he worked.
About Triple point of water (TPW)
The triple point of water is a fundamental thermometric reference: the unique temperature and pressure (273.16 K, 611.657 Pa) at which water coexists simultaneously as solid, liquid, and vapor. When used as a temperature unit, one triple-point unit (TPW) equals 273.16 K, so temperatures are expressed as multiples of this fixed point. This makes 0 TPW equal to absolute zero and 1.000 TPW equal to water's triple point exactly. The freezing point (273.15 K) is 0.9999 TPW — just below 1 — while boiling (373.15 K) is approximately 1.366 TPW. This unit served as the defining reference for the kelvin from 1954 until the 2019 SI revision.
Used in metrology laboratories to calibrate precision thermometers. A sealed triple-point cell containing ultra-pure water held at exactly 273.16 K (0.01°C) serves as a primary temperature standard.
Kelvin – Frequently Asked Questions
How close to absolute zero have scientists actually gotten?
In 2021, researchers at the University of Bremen cooled rubidium atoms to 38 picokelvin (38 trillionths of a kelvin above absolute zero) inside a drop tower — the coldest temperature ever achieved. At these extremes, atoms form a Bose–Einstein condensate where quantum effects become visible at macroscopic scales. True 0 K is impossible to reach (the third law of thermodynamics forbids it), but each new record pushes closer, enabling research into superfluidity, quantum computing, and exotic states of matter.
Why do scientists use kelvin instead of Celsius?
Scientific calculations in thermodynamics, astrophysics, and chemistry require an absolute scale with no negative values. Many physical laws — the ideal gas law (PV = nRT), Wien's displacement law, Stefan–Boltzmann law — only work correctly with absolute temperature. Using Celsius would require constant offsets of 273.15.
What is the difference between kelvin and Celsius?
Kelvin and Celsius have identical degree sizes, so a temperature difference of 5 K equals a difference of 5°C. The only difference is the zero point: 0 K = −273.15°C. To convert: K = °C + 273.15. Kelvin has no negative values; Celsius does.
What everyday temperatures are expressed in kelvin?
Kelvin is rarely used in everyday life but appears in lighting (color temperature — a warm white bulb is around 3,000 K, daylight is 6,500 K), industrial processes, cryogenics (liquid helium: 4.2 K; liquid nitrogen: 77 K), and the specification of laser wavelengths and scientific instruments.
What is the coldest naturally occurring temperature in the universe?
The Boomerang Nebula, a protoplanetary nebula about 5,000 light-years away, has a measured temperature of approximately 1 K (−272°C), making it the coldest known naturally occurring place in the universe — colder than the cosmic microwave background (2.725 K).
Triple point of water – Frequently Asked Questions
What is the triple point of water?
The triple point of water is the unique combination of temperature and pressure (273.16 K / 0.01°C and 611.657 Pa) at which water can coexist as solid, liquid, and gas simultaneously. It is a fixed thermodynamic point that cannot vary — any change in temperature or pressure causes one phase to disappear.
Why was the triple point of water used to define the kelvin?
The triple point is a perfectly reproducible, invariant temperature — it occurs at exactly one pressure and temperature. From 1954 to 2019, the kelvin was defined as 1/273.16 of the thermodynamic temperature of the triple point of water, providing a stable international calibration reference accessible to any metrology lab.
What is the difference between the triple point and the freezing point of water?
The freezing point of water at standard atmospheric pressure is 273.15 K (0.00°C), while the triple point is 273.16 K (0.01°C) at 611.657 Pa. The triple point is 0.01°C warmer and occurs at much lower pressure than normal atmospheric conditions. Both are distinct and precisely defined reference points.
What replaced the triple point of water in the 2019 SI redefinition?
In the 2019 redefinition of SI units, the kelvin was redefined by fixing the value of the Boltzmann constant (k = 1.380649 × 10⁻²³ J/K) exactly. This makes the kelvin independent of any physical substance, more stable, and consistent with other SI redefinitions that fixed fundamental constants rather than relying on material artifacts.
Can the triple point of water occur naturally?
The triple point requires a pressure of about 611 Pa — roughly 0.6% of standard atmospheric pressure. On Earth's surface this does not occur naturally. On Mars, where atmospheric pressure is around 600–700 Pa at the surface, conditions near the triple point of water can occur, meaning liquid water, ice, and water vapor can briefly coexist on the Martian surface under the right conditions.