Watt (W)

The rate at which energy is transferred, measured in joules per second.

1882, in allusion to James Watt (1736-1819), Scottish engineer and inventor.


An undulation or vibration; a form of movement by which all radiant energy of the electromagnetic spectrum is estimated to travel.

"moving billow of water," 1526, from wave (v.), replacing M.E. waw, from O.E. wagian "to move to and fro" (see wag (v.)). Of people in masses, first recorded 1852; in physics, from 1832.

Wave number

The frequency of a wave divided by its velocity of propagation; the reciprocal of wavelength.


A system or material designed to confine and direct electromagnetic waves in a direction determined by its physical boundaries.


The distance from the peak of a wave crest to the peak of the subsequent wave crest, or from one trough to the next trough, expressed in units of distance (e.g. km, m, cm, micron, nm).

To learn more about wavelength, click on the link to the Spectroscopy, Lasers, and Biomedical Optics pamphlets.

Wollaston prism

1) A polarizing prism consisting of two calcite prisms cemented such that they deviate the two emerging beams (which are mutually perpendicularly polarized) by nearly equal amounts in opposite directions. 2) A prism that neither inverts nor reverts the image but will deviate a beam by ninety degrees. It is used in an instrument known as a "Camera Lucida" or "Camera Clara."