Resistance Coil, Standard.
A standard or resistance issued by the Electric Standard Committee of
Great Britain. The cut shows the standard ohm. It is formed either of
German silver, or of an alloy of silver, 66.6 per cent. and platinum,
33.4 per cent. The wire is insulated and doubled before winding as
described before. (See Coil, Resistance.) The two ends of the wire are
soldered, each one to a heavy copper wire or rod r. The whole coil is
enclosed in a brass case, and is enclosed with paraffine melted in at A.
A place for a thermometer is provided at t. By immersing the lower part
of the case B in water of different degrees of heat any desired
temperature can be attained.
Fig. 292. STANDARD OHM COIL.
Resistance, Combined.
The actual resistance of several parallel conductors starting from the
same point and ending at the same point. If the individual resistance be
a b c d .. and the combined resistance be x then we have
x = 1 / (( 1/a) + (1/b) + (1/c) + (1/d) + …)
Synonym--Joint Resistance.
Resistance, Critical.
In a series wound dynamo the resistance of the outer circuit above which
the machine will refuse to excite itself.
Resistance, Dielectric.
The mechanical resistance of a dielectric to the tendency to perforation
or to the strains due to electrification. This is a phase of mechanical
resistance, and is distinct from the electrical or ohmic resistance of
the same substance.
Resistance, Digney Unit of.
The resistance of an iron wire, 1 kilometer long, 4 millimeters
diameter, temperature unknown.
It is equal to 9.163 legal ohms.
Resistance, Electrolytic.
The resistance of an electrolyte to the passage of a current decomposing
it. It is almost entirely due to electrolysis and is added to by
counter- electro-motive force, yet it is not treated specifically as
such, but as an actual resistance. When a current of a circuit of too
low voltage to decompose an electrolyte is caused by way of immersed
terminals to pass through an electrolyte the resistance appears very
high and sometimes almost infinite. If the voltage is increased until
the electrolyte is decomposed the resistance suddenly drops, and what
should be termed electrolytic resistance, far lower than the true
resistance, appears.