## Optics Dictionary

Sometimes reading a scientific explanation is as difficult as reading Parseltongue. This section features definitions and etymology for the terms and phrases you will encounter as you explore the science of light. Etymology is the study of the history of words — when they entered a language, from what source, and how their form and meaning have changed over time. Ever wonder how the word optics got its meaning? OK — probably not but now you can find out!

#### Vertex

General Terms

1) A maximum or minimum of a curve. 2) A point where an optical axis crosses a lens or mirror surface. 3) A point of collision. 4) An angle point of any shape or angle, occurring where two segments, lines, rays or a combination of these cross. 5) A node in a graph. 6) Attributes that describe a point in space.

1570, "the point opposite the base in geometry," from L. vertex "highest point," lit. "the turning point," originally "whirling column, whirlpool," from vertere "to turn." Meaning "highest point of anything" is first attested 1641.

#### Vibrations

General Terms

Oscillations (back and forth movements).

#### Visible

General Terms

1) Able to be seen by the eye. 2) The range of the electromagnetic spectrum that can be seen by the human eye (visible spectrum).

early 14c., from O.Fr. visible, from L. visibilis "that may be seen," from visus, pp. of videre "to see." Visibility "condition of being seen" is from 1581; meaning "range of vision under given conditions" is from 1914.

#### Visible spectrum

General Terms

The part of the electromagnetic spectrum that can be detected and seen with the human eye. It includes the range of wavelengths between 400 nm and 700 nm, where one nanometer is a billionth of a meter $\left(1\text{\hspace{0.17em}}\text{nm}=1×{10}^{-9}\text{\hspace{0.17em}}\text{m}\right)$ , and a range of frequencies between , where one hertz is one cycle per second.

#### Vision

General Terms

1) The ability to see. 2) To have an idea about what something might be in the future.

from L. visionem (nom. visio) "sight, thing seen," from pp. stem of videre "to see." The meaning "sense of sight" is first recorded c.1491.

#### Visual

General Terms

1) Of or relating to sight. 2) An object used to illustrate something.

early 15c., "coming from the eye or sight" (as a beam of light), from L.L. visualis "of sight," from L. visus "sight," from pp. of videre "to see." Meaning "relating to vision" is first attested 1603. The noun meaning "photographic film or other visual display" is first recorded 1951. Visualize is first recorded 1817, said to have been coined by Coleridge.

#### Vitreous

General Terms

Having the characteristics of glass.

1646, from L. vitreus "of glass, glassy," from vitreum "glass."

#### Vitrify

General Terms

To change or make into glass or a glasslike substance, usually by exposure to high temperatures.

1594, from M.Fr. vitrifier, from L. vitrium "glass."

#### Vitriol

General Terms

1) A metal sulfate that has corrosive properties. 2) Sulfuric acid. 3) Something with corrosive properties.

1392, from O.Fr. vitriol, from M.L. vitriolum "vitriol," from neut. of vitriolus, from L.L. vitreolus "of glass," from L. vitreus "of glass, glassy," from vitrium "glass."

#### Vocal folds

General Terms

Often called the ‘vocal cords,’ are made up of two membranes on the sides of our larynx (voice box). We talk by squeezing them close together as the lungs push air between them causing them to vibrate.

To learn more about vocal folds, click on the link to the Acoustics pamphlet.