Simple Electromagnet Does Mystifying Stunt (May, 1932)

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Simple Electromagnet Does Mystifying Stunt

THE well-known barrel of monkeys could produce no more entertainment than an electromagnetic “circus,” consisting of a powerful solenoid magnet and a number of accessories, that you can construct in an evening.

And besides being a source of fun. such a device is highly instructive, and will serve to clear up many of the mysteries of everyday electricity for you.

The electromagnet or solenoid consists of nothing more than a quantity of insulated wire wound on a spool, and provided with a suitable base, connecting wire and plug.

You can obtain a large wood spool from almost any electric shop that does motor repairing; or perhaps the wire you purchase for the magnet will be on a suitable spool. The one illustrated herewith measures approximately 3-3/4 in. long and 3-1/2 in. across the ends.

Winding the Electromagnet The amount of wire you can use varies within considerable limits. About 3 lbs. of No. 22 enameled, cotton-covered magnet wire will do; or you can use 7 lbs. of No. 20, or 15 lbs. of No. 18 wire.

The larger the wire, the less quickly will the coil overheat. If you have access to a screw-cutting lathe or a coil-winding machine, you can do a neat job, putting the wire on in even layers, with a thickness of oiled cloth tape or other insulating material between layers, as shown in Fig. C.

You can do an equally satisfactory job by hand. A few inches of each end of the “wire should project through holes in one end of the spool.

Mount the coil in a vertical position, on a hollow wood base so that a core can be moved up and down through the hole in the spool. The base illustrated in Fig. 5 has sloping sides, and measures 5 in. high, 5-1/4 in. square at the bottom and 4 in. square at the top.

The spool is attached to it by means of two small bolts passing through holes drilled in the end that has the coil wires projecting from it. Also, there is a large hole in the center of the base, corresponding to that in the spool.

Wiring Up the Magnet The flexible electric cord to which the coil terminals are attached enters the base through a hole in one side, and is kept from slipping out by a knot tied near the end.

The best core consists of a bundle of soft iron wires held together by a wrapping of cloth, cord or other binder. The core should be of such size that it can be moved up and down in the spool hole, yet will remain in any position.

It should be of such length that, when the lower end is resting on the table or other surface supporting the coil base, the top end will be flush with the upper end of the spool.

In the model illustrated, this calls for a core 8-3/4 in. long. Instead of a bundle of iron wire, you can use a length of 1/2-in. steel shafting, as shown in Figs. 3 and 6, with almost equal results.

You can operate the coil directly from the 110-volt, alternating current house-supply line; or, if you find that it overheats rapidly, you can interpose a resistance in series with one of the leads. An electric heater element, suitably protected by a guard of some kind, will serve. A number of direct-current experiments also can be performed, using a 6-volt storage battery as a source of power.

Tricks You Can Do With the Coil Now for some tricks with the coil, using 110-volt A.C. current: The jumping ring is a spectacular and amusing performer. Adjust the core so that two-thirds of it projects above the coil, or insert the 2-ft. length of shafting into the hole. Drop over it an aluminum ring—a section of 3/4-in. aluminum tubing an inch or two long will do. as illustrated in Fig. 6.

Turn on the current. The ring will jump up the core and, if it does not fly clear of the core, will bounce up and down in a swing-like manner, finally coming to rest at a point some distance up the core from the coil.

The height attained depends on the weight. A copper ring, consisting of a single loop of copper wire with the ends connected, will do the same thing, but will not climb as high because of its greater weight. The Jumping Ring Trick Now, with the coil current turned on, grasp the aluminum ring in your fingers and hold it down against the coil end. Soon the metal will become warm, and you may find it necessary to let go of it. The energy with which the magnetic force is trying to push the ring away is converted into heat.

With the core end flush with the coil top, lay over it a thick piece of sheet copper as shown in Fig. 6. Turn on the current, and in a short time the copper will become so hot that water, when dropped on it, will sizzle away into steam. It is even possible to fry an egg on this improvised “stove.”

This leads to another interesting stunt. Make a coil by winding, around a bottle or other cylinder an inch in diameter, of 30 to 50 turns of No. 26 insulated magnet wire. Remove the coil from the form, bind it with cord so that it forms a ring, and connect the ends to the terminals of a miniature socket that accommodates a flashlight bulb.

Test the arrangement by bringing the coil near the top of the electromagnet, when the core is all the way down. The lamp should light. If it is too bright, remove some turns from the coil; if too dim, add more.

Secret of the Flashlight Bulb With the coil held snugly against the socket, and the bulb in place, dip the wire and base into melted paraffin, covering everything but the glass bulb. Now, if the paraffined coil is placed in a glass tumbler or beaker of water, and the container is set on top of the electromagnet, the lamp will light, in a manner mystifying to the uninitiated.

Another trick involves a dancing coil. Make a “spring” of fairly fine copper or aluminum wire by winding a dozen turns around a form, and arranging the ends so that they touch each other lightly. Drop the coil over the projecting core of the electromagnet, with the current-turned on. The coil will dance about in a startling manner, with sparks flying from the ends, if everything has been adjusted properly.

You doubtless will work out many more stunts. For instance, you will find that you have the necessary equipment for making 60 cycle noises when a tin can is set on top of the magnet.

  1. mahta says: May 28, 201012:46 am

    I thank you because of your interesting weblog. I am a student of physics and I am very curious to know about why the ring is jumping , why the lamp is lightning and…..
    could you explian them for me compeletely?
    thanks a lot

  2. JMyint says: May 28, 20107:01 am

    According to Lenz’s Law “An induced electric current always flows in such a direction that it opposes the change producing it.” As the aluminum tube moves though the magnetic field a current is set up and that produces a magnetic field of opposite polarity to the magnet. That causes the aluminum ring to be repulsed until pushing it up the rod. Since aluminum doesn’t magnetize the magnetic field collapses whenever the ring stops moving causing it to fall regenerating the field.

    Lenz’s Law is also in part responsible for the light bulb lighting. As a current will be generated in the coil attached to the light bulb. Induction chargers work the same way.

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