VA - Abbreviation for "volt ampere"
vacuum tube - Electron tube evacuated to such a degree that its electrical characteristics are essentially unaffected by the presence of residual gas or vapor. Have been essentially replaced by transistors for amplification and rectification. Cathode ray tubes are still used as display devices.
valence shell - The outermost electron shell for a given atom. The number of electrons in this shell determines the conductivity of the atom.
varactor diode - PN junction diode with a high junction capacitance when reverse biased. Most often used as a voltage controlled capacitor. The varactor is also called: varicap, tuning diode and epicap.
variable capacitor - Capacitor whose capacitance can be change by varying the effective area of the plates or the distance between the plates.
variable resistor - Resistor whose resistance can be changed by turning a shaft. See also "potentiometer and rheostat."
VCR - Abbreviation for "video cassette recorder."
vector - Quantity having both magnitude and direction. Normally represented by a line. Length of the line indicates magnitude and orientation indicates direction.
vector diagram - Arrangement of vectors showing phase relationships between two or more AC quantities of the same frequency.
vertical MOS - Enhancement type MOSFET designed to handle much greater values of drain current than standard E-MOSFET.
very high frequency - (VHF) Electromagnetic frequency band from 30 MHz to 300 MHz.
very low frequency - (VLF) Frequency band from 3 kHz to 30 kHz.
video - Relating to any picture or visual information. From the latin word meaning "I see."
video amplifier - Amplifier having one or mare stages designed to amplify video signals.
virtual ground - Point in a circuit that is always at approximately ground potential. Often a ground for voltage, but not for current.
voice coil - Coil attached to the diaphragm of a moving coil loudspeaker. The coil is moved through an air gap between magnetic pole pieces.
voice synthesizer - Synthesizer that can simulate speech by stringing together phonemes.
volt - Unit of potential difference or electromotive force. One volt is the potential difference needed to produce one ampere of current through a resistance of one ohm.
voltage - (V) Term used to designate electrical pressure or force that causes current to flow.
voltage amplifier - Amplifier designed to build up signal voltage. By design amplifiers can have a large voltage gain or a large current gain or a large power gain. Voltage amplifiers are designed to maximize voltage gain often at the expense of current gain or power gain.
voltage controlled oscillator - Oscillator whose output frequency depends on an input control voltage.
voltage divider - Fixed or variable series resistor network connected across a voltage to obtain a desired fraction of that voltage.
voltage divider biasing - Biasing method used with amplifiers in which two series resistors connected across a source. The junction of the two biasing resistors provides correct bias voltage for the amplifier.
voltage drop - Voltage or difference in potential developed across a component due to current flow.
voltage feedback - Feedback configuration where a portion of the output voltage is fed back to the input of an amplifier.
voltage follower - Operational amplifier circuit characterized by a high input impedance, low output impedance and unity voltage gain. Used as a buffer between a source and a low impedance load.
voltage gain - Also called voltage amplification. Ratio of amplifier output voltage to input voltage usually expressed in decibels.
voltage multiplier - Rectifier circuit using diodes and capacitors to produce a DC output voltage that is some multiple of the peak value of AC input voltage. Cost effective way of producing higher DC voltages. Voltage doublers and voltage triplers are examples.
voltage rating - Maximum voltage a component can withstand without breaking down.
voltage regulator - Device or circuit that maintains constant output voltage (within certain limits) in spite of changing line voltage and/or load current.
voltage source - Circuit or device that supplies voltage to a load.
voltaic cell - Primary cell having two unlike electrodes immersed in a solution that chemically interacts to produce a voltage.
volt-ampere - Unit of apparent power in an AC circuit containing capacitive or inductive reactance. Apparent power is the product of source voltage and current.
voltmeter - Instrument used to measure difference in potential between two points.
volume - Magnitude or power level of audio frequency. Measured in volume units (VU).