Volta's Law of Galvanic Action.
The electro-motive force between any two metals in an electro-chemical
series (see Electro-Chemical Series) is equal to the sum of the
electro-motive forces between all the intervening metals.
Volta's Law of Thermo-electricity.
In a compound circuit, consisting of a number of different metals, all
points of which are at the same temperature, there is no current.
Volt, B. A.
The volt based on the B. A. ohm. It is equal to .9889 legal volt.
Volt, Congress.
The volt based upon the congress or legal ohm; the legal volt.
Volt-coulomb.
The unit of electric work; the watt-second; it is equivalent to
1.0E7 ergs.
.24068 gram degree C. (calorie)
.737337 foot lbs.,
.00134 horse power seconds.
Volt Indicator.
A form of easily read voltameter for use in electric light stations and
for similar work.
Volt, Legal.
The legal volt based upon the legal ohm. It is equal to 1.00112 B. A.
volt.
Voltmeter.
An instrument for determining the potential difference of any two
points.
In many cases it is a calibrated galvanometer wound with a coil of high
resistance. The object to be attained is that it shall receive only an
insignificant portion of current and that such portion shall suffice to
actuate it. If connected in parallel with any portion of a circuit, it
should not noticeably diminish its resistance.
The divisions into which ammeters range themselves answer for
voltmeters. In practice the same construction is adopted for both. The
different definitions of ammeters in disclosing the general lines of
these instruments are in general applicable to voltmeters, except that
the wire winding of the coils must be of thin wire of great length. The
definitions of ammeters may be consulted with the above understanding
for voltmeters.
In the use made of voltmeters there is a distinction from ammeters. An
ammeter is a current measurer and all the current measured must be
passed through it. But while a voltmeter is in fact a current measurer,
it is so graduated and so used that it gives in its readings the
difference of potential existing between two places on a circuit, and
while measuring the current passing through its own coils, it is by
calibration made to give not the current intensity, but the
electro-motive force producing such current.
In use it may be connected to two terminals of an open circuit, when as
it only permits an inconsiderable current to pass, it indicates the
potential difference existing between such points on open circuit. Or it
may be connected to any two parts of a closed circuit. Owing to its high
resistance, although it is in parallel with the intervening portion of
the circuit, as it is often connected in practice, it is without any
appreciable effect upon the current. It will then indicate the potential
difference existing between the two points.