Editing Polarizability (section)

{{Short description|Tendency of matter subjected to an electric field to acquire an electric dipole moment}}
{{About||electromagnetic waves|Polarization (waves)|other uses|Polarization (disambiguation)}}
'''Polarizability''' usually refers to the tendency of matter, when subjected to an [[electric field]], to acquire an [[electric dipole moment]] in proportion to that applied field. It is a property of particles with an [[electric charge]]. When subject to an electric field, the negatively charged electrons and positively charged [[atomic nuclei]] are subject to opposite forces and undergo [[Electric dipole moment|charge separation]]. Polarizability is responsible for a material's [[dielectric constant]] and, at high (optical) frequencies, its [[refractive index]].

The polarizability of an atom or molecule is defined as the ratio of its induced dipole moment to the local electric field; in a crystalline solid, one considers the dipole moment per [[unit cell]].<ref name=":0">{{Cite book|title=The CRC Handbook of Chemistry and Physics|last=Lide|first=David|publisher=The Chemical Rubber Publishing Company|year=1998|pages=12–17}}</ref> Note that the local electric field seen by a molecule is generally different from the macroscopic electric field that would be measured externally. This discrepancy is taken into account by the [[Clausius–Mossotti relation]]  (below) which connects the bulk behaviour ([[polarization density]] due to an external electric field according to the [[electric susceptibility]] <math>\chi = \varepsilon_{\mathrm r}-1</math>) with the molecular polarizability <math>\alpha</math> due to the local field.

[[#Magnetic polarizability|Magnetic polarizability]] likewise refers to the tendency for a [[magnetic dipole]] moment to appear in proportion to an external [[magnetic field]]. Electric and magnetic polarizabilities determine the dynamical response of a bound system (such as a molecule or crystal) to external fields, and provide insight into a molecule's internal structure.<ref name="CERN">{{cite web |author=L. Zhou |author2=F. X. Lee |author3=W. Wilcox |author4=J. Christensen  |title=Magnetic polarizability of hadrons particles from lattice QCD |url=http://cdsweb.cern.ch/record/581347/files/0209128.pdf |publisher=European Organization for Nuclear Research ([[CERN]]) |year=2002 |access-date=25 May 2010}}</ref> "Polarizability" should ''not'' be confused with the [[Permanent magnet|intrinsic magnetic]] or [[Electret|electric]] dipole moment of an atom, molecule, or bulk substance; these do not depend on the presence of an external field.