Physics, Techniques and ProceduresEnergy level
permissible energy state in a system governed by the rules of
quantum theory. This theory predicts and the physical data demonstrate that the constituents of many systems such as atoms can only have certain energies, while others are "forbidden". The permissible energy states of, for instance,
electrons in the
electron shells, and the
protons and
neutrons in a nucleus are called energy levels. As an example, the magnetic dipole of a spin nucleus (e.g. the proton) when placed in an external magnetic field will assume one of only two possible energy states, aligned either with or opposed to the external field. A transition between energy levels is associated with the release or absorption of radiation at a frequency given by e = h
n (where h =
Plancks constant).
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