A see Ampere ac

Phase - Angular relationship between two waves.

Phase angle - Phase difference between two or more waves, normally expressed in degrees.

Phase shift - Change in phase of a wave form between two points, expressed as degrees of lead or lag.

Phase shift oscillator - An oscillator that uses three RC networks in its feedback path to produce the 180° phase shift required for oscillation.

Phosphor - Luminescent material applied to the inner face of a cathode ray tube that when bombarded with electrons will emit light of various colors.

Photoconductive cell - Material whose resistance decreases or conductance increases when exposed to light.

Photoconduction - A process by which the conductance of a material is change by incident electromagnetic radiation in the visible light spectrum.

Photo detector - Component used to detect or sense light.

Photodiode - A semiconductor diode that changes its electrical characteristics in response to illumination.

Photon - Discrete portion of electromagnetic energy. A small packet of light.

Photoresistor - Also known as a photoconductive cell or light dependent resistor (LDR). See photoconductive cell.

Piezoelectric crystal - Crystal material that will generate a voltage when mechanical pressure is applied and conversely will undergo mechanical stress when subjected to a voltage.

Piezoelectric effect - The production of a voltage between opposite sides of a piezoelectric crystal as a result of pressure or twisting. Also the reverse effect which the application of a voltage to opposite sides causes a deformation to occur at the frequency of the applied voltage. (Converts mechanical energy into electrical energy and electrical energy into mechanical energy.)

Plastic film capacitor - Capacitor in which alternate layers of aluminum foil are separated by thin films of plastic dielectric.