Зображення сторінки
[ocr errors][ocr errors][ocr errors][merged small][merged small]
[ocr errors][merged small][merged small][merged small][merged small][ocr errors][ocr errors]

Series Street System using alternating current without transformer.

40—25-volt lamps in series.

[merged small][merged small][ocr errors][ocr errors][ocr errors][merged small][merged small][ocr errors][merged small]

Transformer Alternating System; also showing location of transformer on pole.

[blocks in formation]

Series Motor on Arc Circuit, show-
ing also inside and outside

Cut-out Switches.

Shunt Motor on Incandescent Circuit,
showing also Main Switch

and Rheostat.


THERE are no conductors of electricity that do not offer resistance to the passage of the current. Copper and silver offer the least resistance, yet they have to be subject to careful calculation that there may be no undue waste of energy or material. Such massive bars of copper might be used that the loss in conveying the current through them would be inappreciable, but the interest on the money invested in such amounts of metal would be prohibitive.

The flow of currents of electricity is due to the impressed electro-motive force, and any losses due to the resistance of the wires are expressed in units of this driving power: i e., “volts.” The amount of current flowing in a given conductor is the result of this original electro-motive force divided by the resistance of the wire. Ohms' formula is the foundation of all calculations of this nature. If C represents the current in “amperes,” E the elec

« НазадПродовжити »