# Oscillator, harmonic

A system with one degree of freedom whose oscillations are described by the equation

The phase trajectories are circles, the period of the oscillations, , does not depend on the amplitude. The potential energy of a harmonic oscillator depends quadratically on :

Examples of harmonic oscillators are: small oscillations of a pendulum, oscillations of a material point fastened on a spring with constant rigidity, and the simplest electric oscillatory circuit. The terms "harmonic oscillator" and "linear oscillatorlinear oscillator" are often used as synonyms.

The oscillations of a quantum-mechanical linear oscillator are described by the Schrödinger equation

Here, is the mass of a particle, is its energy, is the Planck constant, and is the frequency. A quantum-mechanical linear oscillator has a discrete spectrum of energy levels, , ; the corresponding eigen functions can be expressed in terms of Hermite functions (cf. Hermite function).

The term "oscillator" is used in relation to (mechanical or physical) systems with a finite number of degrees of freedom whose motion is oscillatory (e.g. a van der Pol oscillator — a multi-dimensional linear oscillator representing the oscillations of a material point situated in a potential force field with a potential which is a positive-definite quadratic form in the coordinates, see van der Pol equation). There is evidently no unique interpretation of the term "oscillator" , or even of "linear oscillator" .

#### References

[1] | L.I. Mandel'shtam, "Lectures on the theory of oscillations" , Moscow (1972) (In Russian) |

[2] | L.D. Landau, E.M. Lifshitz, "Quantum mechanics" , Pergamon (1965) (Translated from Russian) |

#### Comments

#### References

[a1] | V.I. Arnol'd, "Mathematical methods of classical mechanics" , Springer (1978) (Translated from Russian) |

[a2] | L.I. Schiff, "Quantum mechanics" , McGraw-Hill (1949) |

**How to Cite This Entry:**

Oscillator, harmonic. M.V. Fedoryuk (originator),

*Encyclopedia of Mathematics.*URL: http://www.encyclopediaofmath.org/index.php?title=Oscillator,_harmonic&oldid=16351