Sign Convention - Other Sign Conventions

Other Sign Conventions

• The sign choice for time in frames of reference and proper time: + for future and − for past is universally accepted.
• The choice of in the Dirac equation.
• The sign of the electric charge, field strength tensor in gauge theories and classical electrodynamics.
• Time dependence of a positive-frequency wave (see, e.g., the electromagnetic wave equation):
  • (mainly used by physicists)
  • (mainly used by engineers)
• The sign for the imaginary part of permittivity (in fact dictated by the choice of sign for time-dependence)
• The signs of distances and radii of curvature of optical surfaces in optics
• The sign of work in the first law of thermodynamics.

It is often considered good form to state explicitly which sign convention is to be used at the beginning of each book or article.