Fig. 54.
108. Electro-Magnet. Fig. 54. Drive a nail into a board so that it will project about ¾ of an inch. A soft, or wrought-iron, nail is best, but a short, thick wire-nail will do. If you do not have a thick nail, use an iron screw. Wind 3 or 4 layers of insulated copper wire around it, and fasten the bare ends of the wire down with bent pins. Number 24 wire will be found a good size for experimental purposes. Touch the wires leading from the battery to the ends of the coil, and see if the nail will lift pieces of iron.
109. Note. Always leave at least 6 in. of wire at the ends of all coils and windings. This is needed for connections and repairs, as the wire is liable to get broken at any time around the binding-posts.
110. Note. After you have wound wire upon a core or spool, keep it from untwisting by taking a loop or hitch around it with the wire. Fig. 55 shows how this is done. Pull the end of the wire enough to make the loop stay in place.
111. Electro-Magnet. Fig. 56. Cut annealed iron wire into pieces, 3 inches long, straighten them ([App. 28]), and tie them with thread into a bundle about 5⁄16 in. in diameter. Melted paraffine run in between the wires will hold them in together, but stout thread will do. Wind 3 or 5 layers of No. 24 insulated copper wire upon the soft iron core. This is useful for simple experiments, and this idea may be applied to magnets to be used in pieces of apparatus. Hold the bundle of wires in a vise, and file the ends smooth, before winding on the wire. Paraffine should be used to hold the turns of insulated wire together.
| Fig. 55. | Fig. 56. | Fig. 57. |
112. Electro-Magnet. Fig. 57. An electro-magnet with a removable core may be made by winding the wire on a spool. The core is made, as in [App. 82], of soft iron wires, bound together with stout thread. A bolt may be used instead of the wire, but the wire loses its magnetism much quicker than a soft steel bolt would. (Study residual magnetism.) This magnet is strong enough for many purposes, but the wire is too far from the core, on account of the thickness of the wood, to make it efficient. The wire may be wound on by hand, but a winder ([App. 93]) will do much better and quicker work.