Sign convention
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In some physics textbooks and articles, certain quantities are defined with the opposite sign from that which is used in other publications. This lack of standardization is a frequent source of confusion, misunderstandings, and even outright errors. A standard choice of sign for a definition is called a sign convention. Sometimes, this term is used more broadly to include factors of i and 2π.
A noncomprehensive list of sign conventions:
- In relativity, the metric signature could either be +--- or -+++.
- The choice of <math>\pm<math> in the Dirac equation.
- The sign of the field strength tensor in gauge theories and classical electrodynamics.
- The sign of work in the first law of thermodynamics.
- Time dependence of a positive-frequency wave:
- <math>\exp(-i\omega t)<math> (mainly used by physicists)
- <math>\exp(+j\omega t)<math> (mainly used by engineers)
It is often considered good form to state explicitly which sign convention is to be used at the beginning of each book or article.