Editing Normal mode (section)

== In quantum mechanics ==
Bound states 
in [[quantum mechanics]] are analogous to modes. The waves in quantum systems are oscillations in probability amplitude rather than material displacement. The frequency of oscillation, {{mvar|f}}, relates to the mode energy by {{math|1=''E'' = ''hf''}} where {{mvar|h}} is the [[Planck constant]]. Thus a system like an atom consists of a linear combination of modes of definite energy. These energies are characteristic of the particular atom. The (complex) square of the probability amplitude at a point in space gives the probability of measuring an electron at that location. The spatial distribution of this probability is characteristic of the atom.<ref name="FeynmanLectures">{{Cite book |last=Feynman |first=Richard P. |url=https://www.feynmanlectures.caltech.edu/I_49.html#Ch49-S5 |title=The Feynman lectures on physics. Volume 1: Mainly mechanics, radiation, and heat |date=2011 |publisher=Basic Books |isbn=978-0-465-04085-8 |edition=The new millennium edition, paperback first published |location=New York}}</ref>{{rp|I49-S5}}