Opacity (optics)

Encyclopedia : O : OP : OPA : Opacity (optics)

This article or section is in need of attention from an expert on the subject.
Please help recruit one, or improve this page yourself}} if you can. See [discussion page] for details.

Opacity is the state of being impenetrable to light. An opaque object is neither transparent (allowing all light to pass through) nor translucent (allowing some light to pass through). Degrees of opacity are converse to degrees of transparency.

When a wave of light strikes any interface between two substances, each ray of light can be transmitted, reflected or absorbed at this boundary. The arrangement of atoms in an opaque substance allows nearly all of the light rays to be reflected at many different angles. Therefore, very few of the incident light rays are reflected to the viewer's eyes.

In general, the opacity of a gas is a function of its composition, density and temperature.

Applications

Opacity is important in astrophysics when trying to understand how radiation transfer works in stellar atmospheres, and how this affects the spectra and intensity we observe. Here it often has the designation [\kappa_] or [\kappa_] (for being wavelength-dependent or frequency-dependent respectively), and is also called the absorption coefficient.

Another application of opacity would be absorbance. In several types of chemical analysis the instrument is calculating concentration of the sample by its opacity or absorbance. The darker the liquid the higher the concentration. In spectrophotometry the device identifies the sample's constituent substances, again using the sample's absorbance.

From Wikipedia, the Free Encyclopedia. Original article here. Support Wikipedia by contributing or donating.
All text is available under the terms of the GNU Free Documentation License See Wikipedia Copyrights for details.