Changes

==Etymology==

==Etymology==

[[Latin]] opacus

[[Latin]] opacus

*Date: [http://www.wikipedia.org/wiki/17th_Century 1641]

*Date: [https://www.wikipedia.org/wiki/17th_Century 1641]

==Definitions==

==Definitions==

*1 : exhibiting opacity : blocking the passage of radiant [[energy]] and especially [[light]]

*1 : exhibiting opacity : blocking the passage of radiant [[energy]] and especially [[light]]

:b : obtuse, thickheaded

:b : obtuse, thickheaded

==Description==

==Description==

'''Opacity''' is the [[measure]] of impenetrability to [http://en.wikipedia.org/wiki/Electromagnetic_radiation electromagnetic] or other kinds of [http://en.wikipedia.org/wiki/Radiation radiation], especially visible [[light]]. In radiative transfer, it describes the absorption and scattering of radiation in a [[medium]], such as a [[plasma]], dielectric, shielding [[material]], glass, etc. An opaque object is neither [[transparent]] (allowing all light to pass through) nor [[translucent]] (allowing some light to pass through). When light strikes an [[interface]] between two substances, in general some may be [[reflected]], some absorbed, some scattered, and the rest [[transmitted]] (also see [[refraction]]). [[Reflection]] can be diffuse, for example light reflecting off a white wall, or specular, for example light reflecting off a [[mirror]]. An opaque substance transmits very little light, and therefore reflects, scatters, or absorbs most of it. Both mirrors and carbon black are opaque. Opacity depends on the [[frequency]] of the light being considered. For instance, some kinds of glass, while [[transparent]] in the visual range, are largely opaque to [http://en.wikipedia.org/wiki/Ultraviolet ultraviolet light]. More extreme frequency-dependence is visible in the [http://en.wikipedia.org/wiki/Absorption_line absorption lines] of cold gases. Opacity can be quantified in many ways; for example, see the article [http://en.wikipedia.org/wiki/Mathematical_descriptions_of_opacity mathematical descriptions of opacity].[http://en.wikipedia.org/wiki/Opacity_%28optics%29]

'''Opacity''' is the [[measure]] of impenetrability to [https://en.wikipedia.org/wiki/Electromagnetic_radiation electromagnetic] or other kinds of [https://en.wikipedia.org/wiki/Radiation radiation], especially visible [[light]]. In radiative transfer, it describes the absorption and scattering of radiation in a [[medium]], such as a [[plasma]], dielectric, shielding [[material]], glass, etc. An opaque object is neither [[transparent]] (allowing all light to pass through) nor [[translucent]] (allowing some light to pass through). When light strikes an [[interface]] between two substances, in general some may be [[reflected]], some absorbed, some scattered, and the rest [[transmitted]] (also see [[refraction]]). [[Reflection]] can be diffuse, for example light reflecting off a white wall, or specular, for example light reflecting off a [[mirror]]. An opaque substance transmits very little light, and therefore reflects, scatters, or absorbs most of it. Both mirrors and carbon black are opaque. Opacity depends on the [[frequency]] of the light being considered. For instance, some kinds of glass, while [[transparent]] in the visual range, are largely opaque to [https://en.wikipedia.org/wiki/Ultraviolet ultraviolet light]. More extreme frequency-dependence is visible in the [https://en.wikipedia.org/wiki/Absorption_line absorption lines] of cold gases. Opacity can be quantified in many ways; for example, see the article [https://en.wikipedia.org/wiki/Mathematical_descriptions_of_opacity mathematical descriptions of opacity].[https://en.wikipedia.org/wiki/Opacity_%28optics%29]

[[Category: Physics]]

[[Category: Physics]]