kelvin
C2Technical/Scientific
Definition
Meaning
The SI base unit of thermodynamic temperature, defined by setting the Boltzmann constant to exactly 1.380649×10⁻²³ J·K⁻¹.
A scale of absolute temperature where 0 K is absolute zero (the point at which all molecular motion ceases). It is also used colloquially to refer to colour temperature in lighting and photography.
Linguistics
Semantic Notes
The word 'kelvin' is unique as a unit name because it is not capitalized in everyday use ('kelvin' not 'Kelvin'), unlike most eponymous units, though it is capitalized when abbreviated ('K'). It refers to an absolute scale, not a degree scale.
Dialectal Variation
British vs American Usage
Differences
No significant differences in meaning or usage. Pronunciation may vary slightly.
Connotations
Primarily scientific and technical. In both regions, it carries connotations of precision, physics, and foundational measurement.
Frequency
Equally low-frequency in general discourse but standard in scientific, engineering, and technical contexts in both the UK and US.
Vocabulary
Collocations
Grammar
Valency Patterns
[Number] kelvin(s)a temperature of [Number] Kat [Number] kelvinVocabulary
Synonyms
Weak
Usage
Context Usage
Business
Rare, except in specific high-tech industries like semiconductor manufacturing or cryogenics.
Academic
Core vocabulary in physics, chemistry, engineering, and Earth sciences.
Everyday
Very rare. Might be encountered in discussions about LED lighting colour or advanced photography.
Technical
Essential and precise term. Used without definition in peer-reviewed literature.
Examples
By Part of Speech
adjective
British English
- The kelvin scale is fundamental to thermodynamics.
- They needed a kelvin-defined temperature standard.
American English
- The sensor provides a kelvin-specific readout.
- Adjust the kelvin setting on the studio lights.
Examples
By CEFR Level
- Water freezes at 273.15 kelvins.
- The experiment must be conducted at a constant temperature of 4.2 K.
- Warmer light bulbs have a lower colour temperature, around 2700 kelvin.
- The protocol stipulates cooling the sample to within 50 millikelvin of the target.
- The discrepancy was resolved by tracing the calibration back to the primary kelvin standard.
Learning
Memory Aids
Mnemonic
Think of Lord KELVIN who was very COOL – he defined the absolute COLDest possible temperature.
Conceptual Metaphor
SCALE AS A LADDER (ascending from absolute zero), PURITY/ABSOLUTENESS (as a fundamental, not relative, measure).
Watch out
Common Pitfalls
Translation Traps (for Russian speakers)
- False friend with 'Кельвин' – the unit name is not typically capitalised in English running text ('kelvin'), though the symbol 'K' is capitalised.
- Avoid translating as 'градус Кельвина'. It is simply 'kelvin' or 'K' (e.g., 100 K, not 100°K).
Common Mistakes
- Adding 'degree' or the degree symbol (°) before K (incorrect: °K; correct: K).
- Using a plural 's' with the symbol (incorrect: 100 Ks; correct: 100 K).
- Capitalizing the word in mid-sentence (e.g., 'a temperature of 300 Kelvin' is less standard than '300 kelvin').
Practice
Quiz
Which of the following is the correct usage?
FAQ
Frequently Asked Questions
No. The correct term is simply 'kelvins' (or K). Saying 'degrees Kelvin' or using the degree symbol (°K) is an outdated and incorrect usage.
When writing the unit name in full, it is not capitalized in running text (e.g., 'several kelvin'). The symbol is always a capital 'K'. It is capitalized when referring to Lord Kelvin or the scale by its full proper name (e.g., the Kelvin Scale).
They are different scales with different starting points. A change of 1 degree Celsius is equal to a change of 1 kelvin. However, 0 K is absolute zero (-273.15°C), while 0°C is the freezing point of water. So, K = °C + 273.15.
It describes the hue of a light source by comparing it to a theoretical 'black body' radiator at a given temperature. Lower kelvin values (2700K-3000K) are 'warm' yellowish light, while higher values (5000K-6500K) are 'cool' bluish light, mimicking daylight.