Hawkins Electrical Guide v. 04 (of 10) / Questions, Answers, & Illustrations, A progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications

by N. Hawkins

FOOTNOTES:

[1] NOTE.—The term impedance means the total opposition in an electric circuit to the flow of an alternating current, being made up of the actual or ohmic resistance and the apparent resistance due to self-induction, or if the circuit contain also capacity, the resultant apparent resistance due to self-induction and capacity.

[2] NOTE.—The international ohm ÷ B. A. ohm = 1 ÷ .9866. The B. A. ohm ÷ International ohm = 1 ÷ 1.0136. Hence, to reduce British Association ohms to International ohms, divide by 1.0136. or multiply by .9866.

[3] This size can be used only in the shape of flexible cord.

[4] CAUTION.—The size thus obtained should be compared with the table of carrying capacity of wires as given on [page 731] to see if the wires would have to carry more than the allowable current.

[5] NOTE.—In case a larger loss than any given in the table is required, proceed as follows:—Divide the ampere feet by 10 and then refer to column of Actual Volts Lost divided by 10, from which the size of wire is found as before.

[6] NOTE.—Specific gravity is the weight of a given substance relative to an equal bulk of some other substance which is taken as a standard of comparison. Water is the standard for liquids. In the laboratory the specific gravity bottle is often used in determining the specific gravity of a liquid. The capacity of the bottle is 1,000 grains of pure water. When it is filled with spirits of wine and weighed in a balance (together with a counterpoise for the weight of the bottle, which of course is constant), it will weigh considerably less than 1,000 grains; in fact, the bottle will contain only about 917 grains of proof spirit; therefore, taking the specific gravity of water as unity, 1 or 1.000, the specific gravity of spirits of wine is 0.917. If, on the other hand, the bottle be filled with sulphuric acid, it will weigh about 1,850 grains; hence, the specific gravity of sulphuric acid is said to be 1.850. A more convenient method for the automobilist is by the use of the hydrometer.

[7] NOTE.—If the active material in the negative plates extend beyond the ribs of the grid (the supporting frame), it should be at once pressed back into place, care being taken to prevent the plates drying before this is done. The most suitable and convenient method for pressing, is to place between the plates smooth boards of a thickness equal to the distance between the plates and then put the groups under pressure.

[8] NOTE.—The voltage increase or decrease with change in current is practically constant in a given type of cell for any size of cell when the current is referred to a given time rate of charge or discharge; that is, the drop in a large cell or in a small cell, when each is discharged at its four, six or eight hour rate, will be the same. The drop varies somewhat for the condition of the battery charge. For batteries which are one-third discharged, the temperature 60° Fahr., and plates in good condition, the changes in pressure which may be expected between open circuit voltage and the voltage on charge or discharge are given in the above table.