Phi (letter)
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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 |
Obsolete letters | |||
Digamma | Qoppa | ||
San | Sampi | ||
Other characters | |||
Stigma | Sho | ||
Heta | |||
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Greek diacritics |
Phi (uppercase Φ, lowercase φ or ϕ), pronounced [fi] in modern Greek and as [faɪ] in English, is the 21st letter of the Greek alphabet. In modern Greek, it represents [f], a voiceless labiodental fricative. In Ancient Greek it represented [pʰ], an aspirated voiceless bilabial plosive (from which English ultimately inherits the spelling "ph" in words derived from Greek). In the system of Greek numerals it has a value of 500 (φʹ) or 500,000 (͵φ). The Cyrillic letter Ef (Ф, ф) arose from phi.
The lower-case letter (or often its variant, ) is used as a symbol for:
- The golden ratio in mathematics, art, and architecture.
- Euler's totient function φ(n) in number theory; also called Euler's phi function.
- In algebra, group or ring homomorphisms
- The probability density function of the normal distribution in mathematics and statistics.
- An angle, typically the second angle mentioned, after θ (theta). Especially:
- The argument of a complex number.
- The phase of a wave in signal processing.
- In spherical coordinates, mathematicians usually refer to phi as the polar angle (from the z-axis). The convention in physics is to use phi as the azimuthal angle (from the x-axis).
- One of the dihedral angles in the backbones of proteins.
- Internal or effective angle of friction
- Electric potential in physics.
- The work function in electronics.
- A shorthand representation for an aromatic functional group in organic chemistry
- The fugacity coefficient in thermodynamics
- The ratio of free energy destabilizations of protein mutants in phi value analysis
- In cartography and navigation, latitude.
- A sentence in first-order logic.
- Porosity in geology and hydrology.
- Strength (or resistance) reduction factor in structural engineering, used to account for statistical variabilities in materials and construction methods.
- The symbol for a voiceless bilabial fricative in linguistics.
The upper-case letter Φ is used as a symbol for:
- The golden ratio conjugate 0.618... in mathematics.
- The magnetic flux and electric flux in physics, with subscripts distinguishing the two.
- The cumulative distribution function of the normal distribution in mathematics and statistics.
- Philosophy.
- The number of phases in a power system in electrical engineering, for example 1Φ for single phase, 3Φ for three phase.
- The symbol of the voiceless bilabial fricative in the international phonetic alphabet.
The diameter symbol in engineering, ⌀, is often incorrectly referred to as "phi". This symbol is used to indicate the diameter of a circular section, for example "⌀14", means the diameter of the circle is 14 units.
[edit] Computing
In Unicode, there are multiple forms of the phi letter:
- Uppercase:
- U+03A6 GREEK CAPITAL LETTER PHI (Φ): used in Greek texts
- Lowercase:
- U+03C6 GREEK SMALL LETTER PHI (φ): used in Greek texts
- U+03D5 GREEK PHI SYMBOL (ϕ): used in mathematical and technical contexts[1]
- U+0278 LATIN SMALL LETTER PHI (ɸ): used in IPA to symbolise a voiceless bilabial fricative
In HTML/XHTML, the upper and lower case phi character entity references are Φ (Φ) and φ (φ) respectively.
In LaTeX, the math symbols are \Phi (), \phi (), and \varphi ().
In some browsers (e.g. Internet Explorer 6), the shapes of the U+03C6 GREEK SMALL LETTER PHI (which should be viewed as a curl) and U+03D5 GREEK PHI SYMBOL (which should be viewed as a circle crossed by a slash) are exchanged. Compare these samples to check your browser:
Character | Name | Correct appearance | Your browser |
---|---|---|---|
U+03C6 | GREEK SMALL LETTER PHI | φ | |
U+03D5 | GREEK PHI SYMBOL | ϕ |