- the SI symbol for the volt (see
- a common symbol for the voltage in an alternating current (AC)
circuit (see var below for comments on alternating
current). The SI does not allow symbols to
be modified with additional information; instead of "12 VAC,"
write "AC 12 V."
- a traditional unit of mass or weight in countries of the
former Yugoslavia. Originally considered to be the weight that
could be carried by a wagon, the unit has been "metrized" and is
now defined to be equal to the dekatonne,
that is, 10 metric tons or 22 046.23 pounds
- a symbol used in Europe, especially in Germany, for the
- a unit of the reactive electric power delivered by an
alternating current (AC) circuit. In an AC circuit, the electric
potential or voltage (measured in volts) and the current (in
amperes) alternate direction,
varying smoothly according to sine curves. In a purely resistive
circuit, current is in phase with voltage. In a purely inductive
circuit, the variations of the current would lag the variations in
the voltage by 1/4 cycle, or 90°. In real circuits, the
current can be separated into two parts: a part in phase with the
voltage, and the "reactive" part, which lags the voltage by
90°. The reactive part does no net work; it simply heats the
conductor. Reactive current does perform important magnetizing and
voltage-regulation functions in real circuits. The reactive power
is the product of the voltage and the reactive part of the
current. The name of the unit is an acronym for
- a traditional unit of distance in Spanish- and
Portuguese-speaking countries. The length of the vara varied (no
pun intended), but in Spanish Latin America it was generally about
33 inches or a little longer. In
Texas, where it was often used in land measurement, the vara was
defined to equal exactly 33 1/3 inches, which is equivalent to
84.667 centimeters. In California, the vara was considered equal
to 33 inches (83.82 centimeters) and in Mexico the former standard
was 32.993 inches (83.802 centimeters). In southern South America
the vara was usually about 34 inches (86.4 centimeters). The
Spanish vara is shorter; it equals 32.908 inches or 83.587
centimeters. The Portuguese vara, on the other hand, is much
longer; it equals 5 palmos or about
110 centimeters (43.3 inches). The word vara means a stick
- a common symbol for the voltage in a direct current (DC)
circuit. In DC circuits, both voltage and current are constant.
The SI does not allow symbols to be
modified with additional information; instead of "12 VDC," write
"DC 12 V."
- a traditional Russian unit of volume equal to 100 charki.
The vedro is about 12.30 liters (3.249 U.S. liquid gallons
or 2.706 British Imperial gallons). In Bulgaria, the vedro has
also been used informally as a name for the dekaliter (exactly 10
liters or 2.642 U.S. liquid gallons). The word vedro means a
- an old name for the yard, taken
from the Latin word virga for a twig or stick. In modern
French, verge is the customary word for the English
- a traditional unit of land area in the Channel Islands, a
British territory just off the coast of France. The unit varied
from one parish to another. In Jersey, a common estimate is that
the vergee is equal to about 0.44 acre
(about 0.178 hectare or 2130
square yards). In Guernsey it is somewhat smaller, about 0.4 acre
(0.162 hectare or 1940 square yards). The name of the unit is a
old Norman word meaning an orchard.
- vershok or verchok
- a traditional Russian unit of distance equal to 1/16 arshin,
1.75 inches or 4.445 centimeters.
The plural is vershki.
- verst, versta, vehrsta
- a traditional Russian unit of distance, formerly used
throughout eastern Europe. The verst equals 1500 arshin,
which is 3500 feet, 0.662 88
mile, or 1066.8 meters.Although
vehrsta is the best transliteration of the Russian, the
spelling verst is common in English. The German spelling
werst is also used sometimes. In Finnish the unit is called
the virsta. The Russian plural is vehrsty.
- Vickers hardness number (HV or VHN) or
Vickers pyramid number (VPN)
- a measure of the hardness of a metal introduced by Vickers in
1922. In the Vickers test (suitable for surface-hardened metals),
a pyramidal diamond is pressed into the material being tested. The
Vickers hardness is the amount of force applied to the diamond
divided by the area of the indentation the diamond makes in the
material; in practice the diagonal of the pyramidal indentation is
measured and the result, computed in kilograms
of force per square millimeter, is read from a table. (The
reading should be stated as an empirical measurement, without
units.) Up to about HV 500, the Vickers hardness is about 1.04
times the Brinell hardness.
- viertel 
- a traditional unit of volume in several European countries.
Oddly, although the name means "quarter" in German the traditional
viertel is not really 1/4 of any other unit. The Danish viertel
equals 8 pots or about 7.74 liters
(2.04 U.S. liquid gallons or 1.70
British Imperial gallons). In Switzerland the viertel is 40
schoppen, which is exactly 15
liters (3.9626 U.S. liquid gallons or 3.3000 British Imperial
- viertel 
- a unit of volume for wine in Austria, equal to exactly 1/4
liter (250 milliliters) or about 8.45 U.S. fluid
- an obsolete unit of light intensity equal to 20.17 candelas.
One violle is the intensity of a square centimeter of platinum,
glowing at its melting temperature of 1769 °C (3216 °F).
The unit is named for the French physicist Jules Violle
(1841-1923), who proposed it in 1881; it was the first unit of
light intensity that did not depend on the properties of a
- an old English unit of land area equal to 1/4 hide.
This is roughly 30 acres or 12
hectares. The virgate was also
called the yardland or yard of land.
- viscosity grade (VG)
- a commercial rating of industrial lubricants. The grade
numbers are approximately equal to the kinematic viscosity of the
lubricant in centistokes. A
table is provided showing the
range of viscosities acceptable for each grade under the current
standard of the International Organization for Standardization
- a term often used with a Snellen
fraction in phrases such as "20/20 vision."
- viss, vis, vise
- a traditional unit of mass or weight in southern India and
southeast Asia, equal to 100 ticals.
The name is derived from the Tamil visai. The traditional
size of the viss is about 1640 grams (about 3.62 pounds),
but it is currently used in the Southeast Asian drug trade as a
metric unit equal to exactly 1600 grams (1.6 kilograms or 3.527
pounds). This metric unit is called the choi or joi
in Laos and Thailand.
- volcanic explosivity index (VEI)
- a measure of the severity of a volcanic eruption. The VEI
scale is from 0 to 8; an index value of v corresponds to an
output of at least 103+v cubic meters of magma. The Mt.
St. Helens eruption of 1980 was a 5 on this scale, and the largest
eruption of historic times (the Tambora eruption of 1815) rated a
7. A table is provided.
- volt (V)
- the SI unit of electric potential. Separating electric charges
creates potential energy, which can be measured in energy units
such as joules. Electric potential
is defined as the amount of potential energy present per unit of
charge. Electric potential is measured in volts, with one volt
representing a potential of one joule per coulomb
of charge. The name of the unit honors the Italian scientist Count
Alessandro Volta (1745-1827), the inventor of the first battery.
(Note: I am sometimes asked about standard line voltages in
different countries. Steve Kropla has a helpful chart
with this information.)
- volt ampere
- a unit of electrical load used in power engineering. In an
alternating current circuit, if the potential (measured in volts)
and the current (measured in amperes)
vary in phase with each other, then the power delivered (measured
in watts) is the product of the
potential and the current. In actual circuits, the potential and
current are usually out of phase (see var, above), causing the
device receiving the power to draw more current than its wattage
requirements would suggest. The product of the potential and the
actual current is the load, in volt amperes.
- volume unit (vu)
- a unit used in telecommunications to describe the volume of a
radio or television signal carrying complex information such as
speech or music. These waves vary wildly in amplitude in order to
represent the message they carry, so it is difficult to describe
mathematically how large their "average" amplitude is. To solve
this problem, the American Standards Association decided in 1951
to establish as a reference a signal which generates 1 milliwatt
of power in a circuit having an impedance of 600 ohms.
The volume of an incoming signal, in volume units, is equal to the
number of decibels by which it
exceeds this reference level. Thus the volume unit is (in a
complicated way) a variation of the decibel.
- volumetric unit (vu)
- a unit of volume equal to 200 cubic feet (5.663 cubic meters),
used in the U.S. forest products industry for wood chips and other
by-products of lumber production.
- a measure of the size of a package used for billing purposes
in the airline industry. The volumetric weight of a package, in
kilograms, is equal to lwh/6000, where l,
w, and h are the maximum length, width, and
height measurements of the package, in centimeters. Shippers are
billed for the larger of the volumetric weight and the actual
weight of the package. Since the calculation assumes a density of
only 1/6 gram per cubic centimeter (1/6 the density of water), the
volumetric weight is used only for rather light packages that take
up a lot of space on the aircraft.
- an abbreviation for "by volume," used in chemistry and
pharmacology to describe the concentration of a substance in a
mixture or solution. Thus 2% v/v means that the volume of the
substance is 2% of the total volume of the solution or mixture.
See also w/v.
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May 18, 2000