The Standard Electrical Dictionary Part 137

Resistance, External.

In an electric circuit the resistance of the circuit outside of the generator, or battery.

Synonym--Non-essential Resistance.

Fig. 293. RESISTANCE FRAME.

Resistance Frame.

An open frame filled with resistance coils of iron, or German silver wire. It is used as a resistance for dynamos and the larger or working cla.s.s of plant. The coils are sometimes connected so that by a switch moving over a row of studs one or more can be thrown into series according to the stud the switch is in contact with.

Resistance, German Mile Unit of.

The resistance of 8,238 yards of iron wire 1/6 inch in diameter. It is equal to 56.81 legal ohms.

466 STANDARD ELECTRICAL DICTIONARY.

Resistance, Hittorf's.

A high resistance, often a megohm, composed of Hittorf's solution, q. v.

It is contained in a vertical gla.s.s tube near whose upper and lower ends are electrodes of metallic cadmium attached to platinum wires. The cadmium is melted in gla.s.s tubes, the platinum wire is inserted into the melted metal and the tube is broken after all is solid. The resistance should show no polarization current.

Fig. 294. HITTORF'S RESISTANCE

Resistance, Inductive.

A resistance in which self-induction is present; such as a coil of insulated wire wound around an iron core.

Resistance, Insulation.

The resistance of the insulation of an insulated conductor. It is stated in ohms per mile. It is determined by immersing a section of the line in water and measuring the resistance between its conductor and the water.

The section must be of known length, and its ends must both be above the liquid.

Resistance, Internal.

The resistance of a battery, or generator in an electric circuit as distinguished from the resistance of the rest of the circuit, or the external resistance.

Synonym--Essential Resistance.

Resistance, Jacobi's Unit of.

The resistance of a certain copper wire 25 feet long and weighing 345 grains.

It is equal to 0.6296 legal ohm.

Resistance, Matthiessen's Meter-gram Standard.

The resistance of a pure hard drawn copper wire of such diameter that one meter of it weighs one gram. It is equal to .1434 Legal Ohms at 0?

C. (32? F.)

Resistance, Matthiessen's Unit of.

The resistance of a standard mile of pure annealed copper wire 1/16 inch diameter, at a temperature of 15.5? C. (60? F.).

It is equal to 13.44 legal ohms.

467 STANDARD ELECTRICAL DICTIONARY.

Resistance, Meter-millimeter Unit of.

The resistance of a wire of copper one meter long and one square millimeter in section. It is equal to .02057 ohms at 0? C. (32? F.) The term may also be applied to the resistance of similar sized wire of other metals.

Resistance, Mil-foot Unit of.

The resistance of a foot of copper wire one-thousandth of an inch in diameter. It is equal to 9.831 ohms at 0? C. (32? F.) The term may also be applied to the resistance of similar sized wire of other metals.

Resistance, Non-essential.

The resistance of the portion of an electric circuit not within the generator; the same as external resistance.

Synonym--External Resistance.

Resistance, Non-inductive.

A resistance with comparatively little or negligible self-induction.

Resistance of Human Body.

The resistance of the human body is largely a matter of perfection of the contacts between its surface and the electrodes. It has been a.s.serted that it is affected by disease. From 350 to 8,000 ohms have been determined as resistances, but so much depends on the contacts that little value attaches to the results.

Resistance, Ohmic.

True resistance measured in ohms as distinguished from counter-electro-motive force, q. v. The latter is called often spurious resistance.

Synonym--True Resistance.

[Transcriber's note: "True" vs. "spurious" are interesting terms, considering that today we define impedance as a combination of "real"

resistance and "imaginary" capacitive and inductive reactance.]

Resistance, Reduced.

The resistance of a conductor reduced to ohms, or to equivalent lengths of a column of mercury, 1 square millimeter in cross area.

Resistance, Siemen's Unit of.