Glossary

a b c d e f g h i j k l m n o p q r s t u v w

parabolic microphone - a microphone placed at the focal point of a concave or parabolic reflecting surface.

parallax - the apparent shift in the position of an object when viewed from different angles.

parsec - the distance from the sun to a star such that it would have a parallax angle of one second of arc as viewed from the Earth.
1 parsec = 3.09 x 10¹⁶m, or 3.26 light years.

partially reflected ray - some of the incident ray refracts and passes through a medium, while some of the light (partially) simply reflects off the boundary surface.

penumbra - a partial shadow.

period - the time required to complete one cycle.

periodic waves - regular, repeated waves.

physics - the study of phenomena of the physical world.

pinna (ear flap) - ear flap detects the direction of sound and directs the sound to the ear canal and eardrum.

point of incidence - where an incident ray strikes a surface.

polarization (light) - causing the light waves to vibrate in two planes perpendicular to the direction of travel.

potential energy - stored energy. Potential energy is the greatest in solids and least in gases.

precision - the degree of exactness that measurement can be reproduced. The precision of a measuring tool is limited by the graduations or divisions on its scale.

presbyopia - a type of farsightedness that usually appears in older people. It is a result of a loss of elasticity of the lens, causing the lens to not accommodate properly.

primary colours - the three principle colours that can be mixed to produce all other colors. The 3 additive primary colours are red, blue, and green. The 3 subtractive primary colours are yellow, magenta, and cyan.

principal axis - a construction line drawn through the vertex and center of curvature.

principal focus (F) - a point on the principal axis where parallel rays reflect and converge or appear to converge (sometimes called focal point).

pulse - a single wave movement.

pupil - the black aperture (hole) in the iris that lets light pass to the lens.

Top of Page