Difference between revisions of "Relative permittivity"

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<div class="definition"><div class="short_definition">(<br/>''Also called'' dielectric function, dielectric constant, specific inductive capacity.)  The frequency-dependent response of [[optically homogeneous]] matter to excitation by a time-  harmonic [[electric field]].</div><br/> <div class="paragraph">If the electric [[polarization]] '''P''' (average [[dipole moment]] per unit volume) of a material satisfies  the (assumed) constitutive relation  <div class="display-formula"><blockquote>[[File:ams2001glos-Re32.gif|link=|center|ams2001glos-Re32]]</blockquote></div> where &#x003b5;<sub>0</sub> is the [[permittivity]] of [[free space]] (a universal constant), '''E''' is the electric field, and &#x003c7; is  the electric susceptibility, then the (dimensionless) relative permittivity is  <div class="display-formula"><blockquote>[[File:ams2001glos-Re33.gif|link=|center|ams2001glos-Re33]]</blockquote></div> &#x003b5; is a complex-valued function of [[frequency]], its imaginary part related to [[absorption]] of [[electromagnetic  waves]]. Although dielectric constant is often used as a synonym for relative permittivity  (or dielectric function), the former term is misleading given that it may vary by nearly a factor of  100 over the [[electromagnetic spectrum]], and hence can hardly be said to be &ldquo;constant.&rdquo; By the  dielectric constant (or, better, static dielectric constant) of a material is often meant the ratio of  the capacitance of a parallel-plate capacitor with that material between the plates to the capacitance  with a vacuum between them. The [[refractive index]] of a nonmagnetic material is the square root  of its relative permittivity.</div><br/> </div>
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<div class="definition"><div class="short_definition">(''Also called'' dielectric function, dielectric constant, specific inductive capacity.)  The frequency-dependent response of [[optically homogeneous]] matter to excitation by a time-  harmonic [[electric field]].</div><br/> <div class="paragraph">If the electric [[polarization]] '''P''' (average [[dipole moment]] per unit volume) of a material satisfies  the (assumed) constitutive relation  <div class="display-formula"><blockquote>[[File:ams2001glos-Re32.gif|link=|center|ams2001glos-Re32]]</blockquote></div> where &#x003b5;<sub>0</sub> is the [[permittivity]] of [[free space]] (a universal constant), '''E''' is the electric field, and &#x003c7; is  the electric susceptibility, then the (dimensionless) relative permittivity is  <div class="display-formula"><blockquote>[[File:ams2001glos-Re33.gif|link=|center|ams2001glos-Re33]]</blockquote></div> &#x003b5; is a complex-valued function of [[frequency]], its imaginary part related to [[absorption]] of [[electromagnetic  waves]]. Although dielectric constant is often used as a synonym for relative permittivity  (or dielectric function), the former term is misleading given that it may vary by nearly a factor of  100 over the [[electromagnetic spectrum]], and hence can hardly be said to be "constant." By the  dielectric constant (or, better, static dielectric constant) of a material is often meant the ratio of  the capacitance of a parallel-plate capacitor with that material between the plates to the capacitance  with a vacuum between them. The [[refractive index]] of a nonmagnetic material is the square root  of its relative permittivity.</div><br/> </div>
 
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Latest revision as of 16:00, 20 February 2012



relative permittivity

(Also called dielectric function, dielectric constant, specific inductive capacity.) The frequency-dependent response of optically homogeneous matter to excitation by a time- harmonic electric field.

If the electric polarization P (average dipole moment per unit volume) of a material satisfies the (assumed) constitutive relation
ams2001glos-Re32
where ε0 is the permittivity of free space (a universal constant), E is the electric field, and χ is the electric susceptibility, then the (dimensionless) relative permittivity is
ams2001glos-Re33
ε is a complex-valued function of frequency, its imaginary part related to absorption of electromagnetic waves. Although dielectric constant is often used as a synonym for relative permittivity (or dielectric function), the former term is misleading given that it may vary by nearly a factor of 100 over the electromagnetic spectrum, and hence can hardly be said to be "constant." By the dielectric constant (or, better, static dielectric constant) of a material is often meant the ratio of the capacitance of a parallel-plate capacitor with that material between the plates to the capacitance with a vacuum between them. The refractive index of a nonmagnetic material is the square root of its relative permittivity.