- published: 05 Oct 2013
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Phi (uppercase Φ, lowercase φ, or math symbol ϕ), pronounced /faɪ/ FY or sometimes /fiː/ FEE in English, and [ˈfi] in modern Greek, 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 Φ.
The lower-case letter φ (or often its variant, ϕ) is often used to represent the following:
The upper-case letter Φ is used as a symbol for:
The diameter symbol in engineering, ⌀, is often incorrectly[citation needed] 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.
In Unicode, there are multiple forms of the phi letter:
In some older fonts that are not yet compatible with Unicode 3.0 from 1998, the U+03D5 GREEK PHI SYMBOL might be represented by the "loopy" Failed to parse (Missing texvc executable; please see math/README to configure.): \varphi