Calculating the Voltage.—In order to arrive at the voltage we must use a conductor, which, with a resistance of 1 ohm, will produce 1 ampere. It must be remembered that the volt is the practical unit of electro-motive force
While it would be difficult for the boy to conduct these experiments in the absence of suitable apparatus, still, it is well to understand thoroughly how and why these standards are made and used.
CHAPTER VII[ToC]
PUSH BUTTONS, SWITCHES, ANNUNCIATORS, BELLS AND LIKE APPARATUS
Simple Switches.—We have now gone over the simpler or elementary outlines of electrical phenomena, and we may commence to do some of the practical work in the art. We need certain apparatus to make connections, which will be constructed first.
A Two-Pole Switch.—A simple two-pole switch for a single line is made as follows:
A base block (A, Fig. [43]) 3 inches long, 2 inches wide and ¾ inch thick, has on it, at one end, a binding screw (B), which holds a pair of fingers (C) of brass or copper, these fingers being bent upwardly and so arranged as to serve as fingers to hold a switch bar (D) between them. This bar is also of copper or brass and is pivoted to the fingers. Near the other end of the base is a similar binding screw (E) and fingers (F) to receive the blade of the switch bar. The bar has a handle (G) of wood. The wires are attached to the respective binding screws (B, E).