Kappa

 ( Greek Letters ) 

Kappa (; uppercase Κ, lowercase κ or Cursive Greek ; , káppa) is the tenth letter of the Greek alphabet, representing the voiceless velar plosive sound in Ancient Greek and Modern Greek. In the system of Greek numerals, Kʹ has a value of 20. It was derived from the Phoenician letter kaph . Letters that arose from kappa include the Roman K and Cyrillic К. The uppercase form is identical to the Latin K.

Greek proper names and placenames containing kappa are often written in English with "c" due to the Ancient Rome' transliterations into the Latin alphabet: Constantinople, Corinth, Crete. All formal modern romanizations of Greek now use the letter "k", however.

The Greek cursive form is generally a simple font variant of lower-case kappa, but it is encoded separately in Unicode for occasions where it is used as a separate symbol in math and science. In mathematics, the kappa curve is named after this letter; the of this curve were first calculated by Isaac Barrow in the 17th century.

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Symbol

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Lowercase (κ)

Mathematics and statistics

• In graph theory, the connectivity of a graph is given by κ.
• In differential geometry, the curvature of a curve is given by κ.
• In linear algebra, the condition number of a matrix is given by κ.
• The kappa curve, also known as Gutschoven's curve, is a curve whose shape resembles the letter κ.
• Kappa statistics such as Cohen's kappa
  Kilem Li Gwet (2025). 9780970806284, Advances Analytics, LLC. ISBN 9780970806284
  and Fleiss' kappa are methods for calculating inter-rater reliability.

Physics

• In cosmology, the Einstein gravitational constant is denoted by κ.
  Moshe Carmeli (1982). 9780471864370, J. Wiley. ISBN 9780471864370
• In physics, the torsion spring of an oscillation is given by κ.
  David Halliday (2025). 9781119820611, Wiley. ISBN 9781119820611
• In physics, the coupling coefficient in magnetostatics is represented by κ.
  Daniel D. Stancil (1993). 9780387979694, Springer-Verlag. ISBN 9780387979694
• In physics, the dielectric coefficient is represented by κ.
• In fluid dynamics, the von Kármán constant is represented by κ.
• thermal conductivity
• In thermodynamics, the compressibility of a compound is given by κ.
  (2025). 9783540209485, Springer. ISBN 9783540209485

Engineering

• In structural engineering, κ is the ratio of the smaller factored moment to the larger factored moment and is used to calculate the critical elastic moment of an unbraced steel member.
• In electrical engineering, κ is the multiplication factor, a function of the R/ X ratio of the equivalent power system network, which is used in calculating the peak short-circuit current of a system fault. κ is also used to denote conductivity, the reciprocal of resistivity, rho.

Biology and biomedical science

• In biology, kappa and kappa prime are important nucleotide motifs for a tertiary interaction of group II introns.
• In biology, kappa designates a subtype of an antibody component.
• In pharmacology, kappa represents a type of opioid receptor.
  (2025). 9783036543529, MDPI - Multidisciplinary Digital Publishing Institute. ISBN 9783036543529

Psychology and psychiatry

• In psychology and psychiatry, kappa represents a measure of diagnostic reliability.
  John Z. Sadler (2025). 9780198526377, Oxford University Press. ISBN 9780198526377

Economics

• In macroeconomics, kappa represents the capital-utilization rate.

Chemistry

• In chemistry, kappa is used to denote the denticity of the compound.
  Katja A. Strohfeldt (2025). 9780470665589, John Wiley & Sons, Incorporated. ISBN 9780470665589

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Uppercase (Κ)

History

• In textual criticism, the Byzantine text-type (from Κοινη, Koine, the common text).

Mathematics and statistics

• In set theory, kappa is often used to denote an ordinal number that is also a cardinal number.

Chemistry

• In pulping, the kappa number represents the amount of an oxidizing agent required for bleaching a pulp.

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Unicode

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