Fig. 55.
62. Switches have a movable bar or plug of metal, moving on a pivot, to make or break a circuit, or transfer a current from one conductor to another.
Fig. 56 shows a single point switch. The current entering the pivoted arm can go no farther when the switch is open, as shown. To close the circuit, the arm is pushed over until it presses down upon the contact-point. For neatness, both wires are joined to the under side of the switch or to binding-posts.
Fig. 56.
Fig. 57 shows a knife switch. Copper blades are pressed down between copper spring clips to close the circuit. The handle is made of insulating material.
Pole-changing switches, Fig. 58, are used for changing or reversing the poles of batteries, etc.
Fig. 59 shows a home-made switch, useful in connection with resistance coils. By joining the ends of the coils A, B, C, D, with the contact-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. If E be turned to 1, the current will be obliged to pass through all the coils A, B, etc., before it can pass out at Y. If E be moved to 3, coils A and B will be cut out of the circuit, thus decreasing the resistance to the current on its way from X to Y. Current regulators are made upon this principle. (See "Apparatus Book," Chapter IV., for home-made switches.)
