Changes

==Origin==

==Origin==

[[Latin]] ''excitāre'', frequentative of ''exciēre'' to set in [[motion]], [[awaken]], call forth, instigate, < ex- out + ciēre to set in [[motion]].

[[Latin]] ''excitāre'', frequentative of ''exciēre'' to set in [[motion]], [[awaken]], call forth, instigate, < ex- out + ciēre to set in [[motion]].

*[http://en.wikipedia.org/wiki/14th_century 14th Century]

*[https://en.wikipedia.org/wiki/14th_century 14th Century]

==Definitions==

==Definitions==

*1a : to call to [[activity]]  

*1a : to call to [[activity]]  

==Description==

==Description==

'''Excitation''' is an elevation in [http://en.wikipedia.org/wiki/Energy_level energy level] above an [[arbitrary]] baseline [[energy]] state. In [[physics]] there is a specific technical [[definition]] for energy level which is often associated with an atom being excited to an excited state.

'''Excitation''' is an elevation in [https://en.wikipedia.org/wiki/Energy_level energy level] above an [[arbitrary]] baseline [[energy]] state. In [[physics]] there is a specific technical [[definition]] for energy level which is often associated with an atom being excited to an excited state.

In [[quantum mechanics]] an excited [[state]] of a [[system]] (such as an [[atom]], [[molecule]] or [[nucleus]]) is any quantum state of the system that has a higher [[energy]] than the [http://en.wikipedia.org/wiki/Ground_state ground state] (that is, more energy than the absolute minimum). The [[temperature]] of a group of [[particles]] is indicative of the level of excitation (with the notable exception of systems that exhibit [http://en.wikipedia.org/wiki/Negative_temperature Negative temperature]).

In [[quantum mechanics]] an excited [[state]] of a [[system]] (such as an [[atom]], [[molecule]] or [[nucleus]]) is any quantum state of the system that has a higher [[energy]] than the [https://en.wikipedia.org/wiki/Ground_state ground state] (that is, more energy than the absolute minimum). The [[temperature]] of a group of [[particles]] is indicative of the level of excitation (with the notable exception of systems that exhibit [https://en.wikipedia.org/wiki/Negative_temperature Negative temperature]).

The lifetime of a [[system]] in an excited state is usually short: [[spontaneous]] or induced emission of a quantum of energy (such as a [http://en.wikipedia.org/wiki/Photon photon] or a [http://en.wikipedia.org/wiki/Phonon phonon]) usually occurs shortly after the system is promoted to the excited state, returning the system to a state with lower energy (a less excited state or the ground state). This return to a lower energy level is often loosely described as decay and is the [[inverse]] of excitation.

The lifetime of a [[system]] in an excited state is usually short: [[spontaneous]] or induced emission of a quantum of energy (such as a [https://en.wikipedia.org/wiki/Photon photon] or a [https://en.wikipedia.org/wiki/Phonon phonon]) usually occurs shortly after the system is promoted to the excited state, returning the system to a state with lower energy (a less excited state or the ground state). This return to a lower energy level is often loosely described as decay and is the [[inverse]] of excitation.

Long-lived excited states are often called [http://en.wikipedia.org/wiki/Metastable metastable]. Long-lived [http://en.wikipedia.org/wiki/Nuclear_isomer nuclear isomers] and [http://en.wikipedia.org/wiki/Singlet_oxygen singlet oxygen] are two examples of this.[http://en.wikipedia.org/wiki/Excited_state]

Long-lived excited states are often called [https://en.wikipedia.org/wiki/Metastable metastable]. Long-lived [https://en.wikipedia.org/wiki/Nuclear_isomer nuclear isomers] and [https://en.wikipedia.org/wiki/Singlet_oxygen singlet oxygen] are two examples of this.[https://en.wikipedia.org/wiki/Excited_state]

[[Category: Physics]]

[[Category: Physics]]