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# Kappa (Κ, κ) Definition

Kappa (Κ, κ) 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, 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.

Greek proper names and placenames containing kappa are often written in English with c due to the Romans' transliterations into the Latin alphabet: Constantinople, Corinth, Crete. All formal modern romanizations of Greek now use the letter k, however. The cursive form ϰ 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 tangents of this curve were first calculated by Isaac Barrow in the 17th century.

## Usage in Mathematics & Science

The uppercase Kappa (Κ) is used for:

• History:

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

• Mathematics & Statistics:

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

• Chemistry:

• In chemistry, kappa is used to denote the denticity of the compound.

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

The lowercase Kappa (κ) is used for:

• Mathematics & 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.

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

• Physics:

• In cosmology, the curvature of the universe is described by κ.

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

• In physics, the coupling coefficient in magnetostatics is represented by κ.

• In fluid dynamics, the von Kármán constant is represented by κ.

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

• 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 notate conductivity, the reciprocal of resistivity, rho.

• Biology & 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.

• Psychology & Psychiatry:

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

• Economics:

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

## Greek Alphabet

The letters of the Ancient Greek Alphabet, which are frequently utilized in math and science:

 Greek Alphabet Symbol Letter Symbol Letter Uppercase Lowercase Uppercase Lowercase Α α Alpha Ν ν Nu Β β Beta Ξ ξ Xi Γ γ Gamma Ο ο Omicron Δ δ Delta Π π Pi Ε ε Epsilon Ρ ρ Rho Ζ ζ Zeta Σ σ Sigma Η η Eta Τ τ Tau Θ θ Theta Υ υ Upsilon Ι ι Iota Φ φ Phi Κ κ Kappa Χ χ Chi Λ λ Lambda Ψ ψ Psi Μ μ Mu Ω ω Omega

### Sources

“Kappa.” Wikipedia, Wikimedia Foundation, 9 Apr. 2020, en.wikipedia.org/wiki/Kappa.

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