| Fig. 23. | Fig. 24. |
55. Switch. Fig. 24. This simple switch has but one contact point, D, which is a screw-head. This switch may be used anywhere in the circuit by simply cutting the wire carrying the current, and joining the ends of the wire to the binding-posts X and Y. The metal strip, E, is made of 2 or 3 thicknesses of tin. It is ⅝ in. wide and about 5 in. long, and presses down upon D, when swung to the left, thus closing the circuit. The short metal strips shown are ⅝ × 1¼ in. The upper strip is joined to the end of E by a coiled copper wire, C W. (See [App. 50].) If the current enters by the wire, A, it will pass through C W, E, D and out at B. The strip E is pivoted at F by a small screw. The base may be 3 or 4 × 5 × ⅞ in.
56. Switch. Fig. 25. By increasing the number of contact points and the wires leading from them, a switch may be made to throw in one or more pieces of apparatus. This variety of switch is useful in connection with resistance coils (Index). By joining the ends of the coils with the points 1, 2, 3, etc., more or less resistance can be easily thrown in by simply swinging the lever, E, around to the left or right. The uses of this will be again referred to.
Details. The base of the one shown in Fig. 25 is 4 × 5 × ⅞ in. thick. The switch, E, is a band of 2 thicknesses of tin ⅝ in. wide. It is pivoted at F with a screw. To the end of E is fastened a copper wire, which leads to the upper binding-post, X ([App. 46]). The apparatus has 5 contact points, marked 1, 2, 3, etc. These consist of brass screws and copper washers. With F as a center draw the arc of a circle that has a radius of 4 in. Place the screws 1, 2, etc., along this arc, and about ⅝ in. apart, center to center; that is, the screws are all 4 in. from F, and are, therefore, in the form of a curve.
The last screw forms a part of the binding-post, Y. Suppose 4 pieces of apparatus, marked A, B, C, and D, be connected with 1, 2, etc., as shown. These may be, for example, coils of wire to be used as resistance coils. If the current enters at X, it will pass along at E and be ready to leave at Y, as soon as E touches one of the contact points. If E be placed upon 1, the current will be obliged to pass through all of the coils, A, B, etc., before it can get to Y. In this case the resistance will be greatest. If E be now moved on to 2, only A will be cut out, and the total resistance reduced. By placing E upon 4, but one coil, D, will be in the circuit. When E is upon 5 the current will pass through the switch with practically no resistance. This is the principle upon which current regulators work. (Study resistance in text-book.) When E is in the position shown in Fig. 25 no current can pass.