Va

VA
Abbreviation of VoltAmpere, the product of rms voltage and rms current in an electronic circuit. It is the unit of apparent power in the International System of Units (SI).
VAC
Abbreviation of Voltage Alernating Current, normally given as the RMS value.
Vacancy
An unfilled lattice site in a crystal structure.
Vacuum
A given space filled with gas at pressures below atmospheric pressure.
Vacuum Bag Moulding
A moulding technique in which the part is cured inside a layer of film, from which entrapped air is removed by vacuum.
Vacuum Brazing
Components are heated in a high vacuum, completely free of oxygen.
Vacuum Dehydration
A method which involves drying or freeing of moisture through a vacuum process.
Vacuum Distillation
A distillation method which involves reducing the pressure above a liquid mixture to be distilled to less than its vapour pressure.
Vacuum Energy
Underlying background energy that exists in space even when devoid of matter.
Vacuum Engine
The working principle is similar to the hot air engine, except that this engine draws hot air into the cylinder.
Vacuum Gauge
An instrument for measuring pressure below atmospheric pressure.
Vacuum Pump
Device used for creating vacuums.
Vacuum Separator
A separator that utilizes sub-atmospheric pressure to remove certain gases and liquids from another liquid because of their difference in vapour pressure.
Vacuum Test Chamber
A pressure vessel, typically spherical or cylindrical, that can be pumped down to a near vacuum.
Vacuum Tube
An electron tube evacuated to such a degree that its electrical characteristics are essentially unaffected by the presence of residual gas or vapour.
Vacuum Zero
The energy of an electron at rest in empty space, used as a reference level in energy band diagrams.
Valence
The charge on an ion based on the number of electrons transferred or shared within a specific structure.
Valence Band
Highest filled or almost filled band in a semiconductor.
Valence Bond
In the valence bond theory, a valence bond is a chemical bond formed by overlap of half-filled atomic orbitals on two different atoms.
Valence Electrons
The electrons in the outermost shell of an atom.
Valence Shell
The electrons in the outermost shell of an atom.
Valence Shell Electron Pair Repulsion Theory
A model that explains the shapes of molecules by assuming that electron pairs arrange themselves around atoms in a way that minimizes electron-electron repulsions.
Valid Inequality
An inequality constraint added to a relaxation that is redundant in the original mathematical program.
Valve
In electronics, a valve is a device consisting of two or more metal plates enclosed in an evacuated glass bulb.
Valve Bounce
If the speed of valve is closing too high, the valve can hit the seat so hard it bounces off again.
Valve Float
A high-rpm engine condition in which the valve lifters lose contact with the cam lobes because the valve springs are not strong enough to overcome the momentum of the various valvetrain components.
Valve Lifter
The cylindrically shaped component that presses against the lobe of a camshaft and moves up and down as the cam lobe rotates.
Valve Overlap
The amount of time that the inlet and exhaust valves are open at the same time, to allow momentum charging of the cylinder or to scavenge additional exhaust gas from the cylinder.
Valve Regulated Lead Acid Battery
A lead acid battery that uses pressure valves that open only under extreme conditions.
Valve Seat
That part of the valve mechanism upon which the valve face rests to close the port.
Valve Spring
The spring which is used to close a valve.
Valves
Signifies the total intake and exhaust valves in an internal combustion engine.
Valve-Spring Retainer
Holds the valve spring in a state of compression.
Valvetrain
The collection of parts that make the valves operate in an internal combustion engine.
Van Allen Belts
Radiation belts of high-energy particles trapped in the earth's magnetosphere.
Van de Graaff Generator
An electrostatic generator which employs a system of conveyor belt and spray points to charge an insulated electrode to a high potential.
van der Waals Bond
A secondary interatomic bond between adjacent molecular dipoles, which may be permanent or induced.
van der Waals Equation
An equation for non-ideal gasses that accounts for intermolecular attraction and the volumes occupied by the gas molecules.
van der Waals Force
A force acting between nonbonded atoms or molecules. Includes dipole-dipole, dipole-induced dipole, and London forces.
van der Waals Radius
One half the distance between two nonbonded atoms, when attractive and repulsive forces between the atoms are balanced.
Vanadium
The principal use for vanadium is as an alloying constituent, particularly in steels where it is introduced as ferrovanadium, an alloy of iron and vanadium.
Vane Compressor
Sliding-vane compressors use an eccentrically-mounted cylinder to drive centrally-mounted vanes inside a housing of decreasing radius, providing internal compression.
Vanes
Baffles employed to deflect the flow of a fluid, gas or liquid.
Vanishing Line
The horizon; in a drawing it is at the height of viewer′s eye.
Vanishing Point
The point in space where two parallel lines seem to meet.
V Antenna
A bidirectional antenna, shaped like a V, which is widely used for communications.
Vapour
A gas whose temperature is below its critical temperature, so that it can be condensed to the liquid or solid state by increase of pressure alone.
Vapour Barrier
A moisture-impervious layer applied to the surfaces enclosing a humid space to prevent moisture travel to a point where it may condense due to lower temperature.
Vapour Lock
A condition where liquid flow is impeded by vapour trapped in a liquid line.
Vapour Pressure
The partial pressure of a gas in equilibrium with a condensed form (solid or liquid) of the same substance.
Vapour Trail
A cloud like streamer or trail often seen behind aircraft flying in clear, cold, humid air.
Vapourization
A phase transition from the liquid or solid phase to gas phase.
VAr
Abbreviation of Volt Amperes Reactive.
Varactor
A p-n junction diode that is designed to act as a voltage controlled capacitance when it is operated under reverse bias.
Varactor Modulator
An FM modulator that uses a voltage-variable capacitor.
Variable
A letter that is used to represent a numerical quantity whose value may or may not yet be known.
Variable Attenuator
An attenuator for reducing the strength of an AC signal either continuously or in steps, without causing signal distortion.
Variable Cycle
Succeeding sequences are started by the completion of the previous sequence rather than at predetermined intervals.
Variable Displacement Pump
A pump in which the displacement per cycle can be varied.
Variable Geometry Wing
Wings which, fully extended, give the best low-speed performance for take-off and landing, and can be swept in flight to optimum positions for best cruising and high-speed flight performance.
Variable Mu Tube
An electron tube in which the control grid wires are farther apart at the centres than at the ends.
Variable Rate Spring
A spring that does not offer uniform resistance to compression.
Variable Resistor
A wire-wound or composition resistor, the value of which may be changed over a designed range.
Variance
The square of the difference from the mean for each data value, summed and divided by one less than the number of values.
Variate
Random variable.
Variometer
An instrument for comparing magnetic forces, especially of the earth′s magnetic field.
Varistor
A two-electrode semiconductor device having a voltage- dependent nonlinear resistance.
Varnish
A resin in solution.
Varnished Cambric
Cotton cloth coated with insulation varnish.
Vault
An arched brick or stone ceiling or roof.
VAWT
Abbreviation of Vertical Axis Wind Turbine.