Kappa

Greek alphabet
Αα	Alpha	Νν	Nu
Ββ	Beta	Ξξ	Xi
Γγ	Gamma	Οο	Omicron
Δδ	Delta	Ππ	Pi
Εε	Epsilon	Ρρ	Rho
Ζζ	Zeta	Σσς	Sigma
Ηη	Eta	Ττ	Tau
Θθ	Theta	Υυ	Upsilon
Ιι	Iota	Φφ	Phi
Κκ	Kappa	Χχ	Chi
Λλ	Lambda	Ψψ	Psi
Μμ	Mu	Ωω	Omega
History
Archaic local variants  ·  ·  ·  ·  ·
Ligatures (ϛ, ȣ, ϗ) · Diacritics
Numerals: (6) · (90) · (900)
In other languages
Bactrian  · Coptic  · Albanian
Scientific symbols
Book  · Category · Commons

Kappa (uppercase Κ, lowercase κ or ϰ; Greek: κάππα) is the 10th letter of the Greek alphabet, used to represent the /k/ sound in Ancient and Modern Greek. In the system of Greek numerals it 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.

Greek proper names and placenames containing kappa are often written in English with "c" due to contemporary rendering into the Latin alphabet by ancient Romans. However, modern transliteration of the Greek language invariably use the letter "k". Compare Κυνοσκεφαλαι, Cynoscephalae (ancient placename); κυνος κεφαλαι, kunos kephalai (phrase), meaning "dog's heads".

In mathematics, the kappa curve is named after this letter; the tangents of this curve were first calculated by Barrow (17th Century).

Symbol

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 physics, the torsional constant of an oscillator is given by κ as well as Einstein constant of gravitation.

In structural design, 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, it 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.

In chemistry, the compressibility of a compound is given by κ.

In psychology and psychiatry, kappa represents a measure of diagnostic reliability.

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 receptors.

Kappa statistics such as Cohen's kappa and Fleiss' kappa are methods for calculating inter-rater agreement.

Upper-case letter Κ is used as a symbol for:

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

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