A sinusoidal magnitude is characterized by an equation of the type:

V(t) = A sin(2πft + φ)

- A: Amplitude of the signal. V(t) will have the same units as A.
- 2πft + φ: the argument or phase of the function expressed in radians.
- f: frequency of the signal expressed in Hertz. One sometimes manipulates the pulsation, ω = 2πf, the units of which are rad.s
^{-1.}. - Φ is the phase at the origin (time zero) expressed in radians.

A phasor (for Phase Vector) is a representation of sinusoidal function by just taking the amplitude and the phase of origin into account. This representation is very useful in optics or in electronics, for summing, taking the derivatives/integrals of sinusoidal functions of the same frequency, but of different amplitudes and phases.