Fig. 79.—Magnetic Phantom formed about a Wire carrying a Current of Electricity.
This is readily shown by punching a small hole in a piece of cardboard, and passing a wire carrying a strong current of electricity through the hole.
If a few iron filings are sifted on the cardboard and the latter jarred slightly with a pencil as they fall, they will arrange themselves in circles with the wire at the center, forming a magnetic phantom and showing the paths of the lines of magnetic force.
Fig. 80.—Magnetic Phantom formed about several Turns of wire.
By forming the wire into a coil as in Figure 80 the magnetic field generated is much stronger and more plainly seen, for then the combined effect of the wires is secured.
Fig. 81.—Paper Tube wrapped with Wire for Experimental Purposes.
Roll up a small paper tube about 1/2 inch in diameter and four inches long. Wind neatly on the tube three layers of No. 18 insulated copper wire. Pass an electric current through it from two or three cells of a battery, and test its magnetic properties by bringing it near a compass needle. It will be found that the coil possesses very marked magnetic properties, and will readily cause the needle to swing about, even though it is held quite a distance away.
If an iron bar is placed inside of the paper tube, the magnetic effect will be greatly increased.