Glossary

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absolute index of refraction - the ratio of the speed of light in a vacuum (c) to the speed of light in another given medium (v).

absolute zero - the lowest temperature possible, 0 Kelvin or -273°C. Absolute zero is the temperature where all molecular movement would stop and zero energy would be present. Absolute zero can never be reached.

accommodation- the ability of the eye to change its focal length. This is accomplished by the muscles around the lens making the lens flatter or more oval in order to refract the light more or less so you can see near and distant objects clearly.

accuracy - the extent that a measurement agrees or compares with an accepted value or standard.

achromatic lens - a concave and a convex lens joined in a special fashion that eliminates dispersion and ringed colors around the image of an object that normally appear from using a single lens.

acoustics - the manner in which sound is transmitted, reflected, absorbed or dispersed. The term acoustics is generally used when describing the nature of sounds in specific rooms.

amplitude - the distance from rest position or equilibrium to the crest or trough of a wave.

anechoic - rooms that use special materials to make the room "dead" with the reverberation time close to zero.

angle of deviation - when light passes from air into glass and then back into air, if the refracting surfaces are not parallel (like a prism), then the emerging ray takes a different path than the initial incident ray. The angle between the emerging ray and the incident ray is called the angle of deviation.

angle of incidence - the angle between the incident ray (or wave) and a normal.

angle of reflection - the angle between the reflected ray (or wave) and a normal.

angle of refraction - the angle between the refracted ray and the normal.

antinodes (loops) - double crests and double troughs in a standing wave.

aperture - the adjustable opening in a camera or microscope that lets in the light.

astigmatism - results if the cornea or lens of the eye is not shaped perfectly spherical (shaped more like a football than a basketball). The result is light being focused in several different planes.

astronomical telescope - a telescope for viewing distant objects like stars, moons, planets. Astronomical telescopes use 2 converging lenses and the image appears inverted.

astronomical unit (A.U.) - the length on the semimajor axis of the Earth's orbit.
1 A.U. = 1.50 x 10¹¹m

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