Читать книгу Harper's Electricity Book for Boys - Joseph H. Adams - Страница 21

A simple induction or shocking coil may be made of a two-and-one-half by five-sixteenths-inch bolt, a thin wooden spool, and two sizes of insulated copper wire. An induction-coil is a peculiar and wonderful apparatus; it figures largely in electrical experimenting and is a part of every complete equipment.

A piece of curtain-pole may be used for the spool. First bore a five-sixteenths-inch hole through the wood to receive the bolt; then in a lathe turn it down into a spool with less than one-eighth of an inch of wood about the hole and with flanges about one-eighth of an inch in thickness. Smooth the spool with sand-paper, while it is still in the lathe, and give it a thin coat or two of shellac.

Slip the spool on the winder (Fig. 7) and wind on three layers of No. 24 cotton-insulated copper wire, taking care to wrap the coils evenly and close. Bring six inches of the ends out at either end of the spool through small holes pierced in the flanges; then wrap several thicknesses of brown paper around the coil. A current passing around this three-layer coil will magnetize the bolt. This is the primary coil and the one through which the battery current will pass.

A secondary coil is now made over the primary one with eleven or thirteen layers of No. 30 insulated copper wire. It will take some time to carefully put on these layers, and when doing so mark down each layer so as to keep an accurate count, for there must be the right number of layers to make the coil act properly. No. 30 wire is quite fine, and if the layers are not inclined to lie smooth, make a wrap or two of brown paper between each three layers. Bring six inches of each end of the wire out from the flanges of the spool, and to protect the outer coil wrap paper about the coils and attach it fast with thread or paraffine. Slip the bolt through the hole and screw the nut on the threaded end. Cut out a wooden block four inches long, three inches wide, and three-quarters of an inch thick, and with two thin metal straps and screws attach the coil to the middle of the block, as shown in Fig. 8. Make four binding-posts and screw them fast at the corners, and to A and B of Fig. 8 attach the ends of the heavy wire from the primary coil, and to C and D of Fig. 8 the ends of the fine wire from the secondary coils. The induction-coil is now ready for any use to which it may be put, and by mounting it on the block with the delicate wire ends attached to the binding-posts, it is in less danger of damage than if the wire ends were left loose for rough-and-ready connections.

In order to get a shock from this coil it will be necessary to have a pair of handles and a current interrupter. The handles may be made from two pieces of tin rolled into the form of cylinders to which wires are soldered. Or, better yet, use pieces of thin brass tubing an inch in diameter. The buzzer shown in Fig. 9 may be employed for a current interrupter, and a bichromate battery will furnish the current.

In order to make the connections, the wires from the handles are attached to the binding-posts C and D in Fig. 8—that is, to the wires of the secondary coil. One spool of the battery is connected with A of Fig. 8 and the other with A of Fig. 9. A wire connects C of Fig. 9 with B of Fig. 8, and the circuit is closed. The buzzer now begins to vibrate, and any one holding the handles will receive a shock the intensity of which depends on the strength of the batteries. A switch should be introduced somewhere in the circuit, so that it may be opened or closed at will; a good place for it is between a battery-pole and the binding-post A in Fig. 8.

If the shock is too intense it may be weakened by drawing the carbon and zinc poles partly out of the bichromate solution; or a regulator may be made of a large glass tube and a glass preserving-jar filled with water. If the tube cannot be had, an Argand gas-burner chimney will answer as well.

Solder a wire to the edge of a small tin or copper disk, as shown in Fig. 10, on which the chimney rests at the bottom of the jar, and another wire to a tin box-cover with some small holes punched in its top, this latter being suspended within the chimney. This second wire is passed out through a cork at the top of the chimney made of a disk of cardboard and a piece of wood. One wire is connected with A of Fig. 8 and the other with a battery-pole. This apparatus acts the same as a resistance-coil, and by raising or lowering the box-cover the current is increased or diminished. The closer the cover comes to the disk the stronger the current, as there is less water for the electricity to pass through and therefore less resistance; while if the cover touches the disk the current flows as freely as if there were no regulator and the wires ran directly to the cell.

An apparatus comprising a coil, an interrupter, or armature, and a switch may be set on one block, and the arrangement of the several parts is clearly shown in the drawing of the complete galvano-faradic apparatus (Fig. 11). The block should be six inches long, four inches wide, and seven-eighths of an inch in thickness.

The coil is made as described for Fig. 8, the spool being three inches long and one inch and a quarter in diameter. A carriage-bolt three inches and a half long and five-sixteenths of an inch in diameter, with a bevelled head, is made fast in the spool, and this coil is strapped to the block with two metal bands and screws. Two binding-posts (A and B of Fig. 11) are arranged at the upper corners, and to these the ends of the secondary coil wires are attached. Two more binding-posts (C and D of Fig. 11) are arranged at the lower side and provided with a switch to open and close the circuit. One of the primary coil wires is made fast to C, and the other one to a block which contains the set-screw that bears against the vibrating armature. Its arrangement and the wire connection is explained in Fig. 9 B.

An armature of thin brass or tin is made and attached to a block (E in Fig. 11). At the loose end that is opposite the bolt-head several wraps of tin are made and soldered fast, or a small block of soft iron may be riveted to the armature. It must be of iron or tin, however, so as to be attracted by the electro-magnetized bolt-head. This arrangement may be seen in Fig. 12. Attach a thick piece of paper over the bolt-head, so that the lug at the end of the armature will not adhere to it through residual magnetism.

In regular galvano-faradic machines the current regulator is formed of a hollow cylinder which is drawn from the core of the coil; but in this simple machine the water-jar regulator may be connected between a pole of the battery and the binding-posts (D or E of Fig. 11). The wires of the handles are attached to posts (A and B of Fig. 11), and when all the wires are in place and the current turned on by means of the switch, the vibrator begins to work and the shocking-current is felt through the handles. By means of the regulating-screw that bears on the armature, the number of vibrations may be increased or diminished, but for faradic purposes the vibrations should be as quick as possible. Much amusement may be had with this apparatus, and a large number of people may be given a shock by getting them to join hands when standing or sitting in a circle.