By forming the wire into several loops or a spiral the combined effect of all the individual turns is concentrated in a small space and a much more powerful field is produced. If the coil is provided with an iron core, the magnetism is much more concentrated and will exercise a very powerful attractive effect upon any neighboring masses of iron or steel. Such a coil is called an electromagnet.
FIG. 2.—If a wire carrying a current of electricity is formed into a loop, the space enclosed by the loop will become magnetic. The arrows represent the paths of the lines of magnetic force.
Electromagnets play a very important part in the construction of electric motors. The strength of an electro magnetic coil is proportional to its ampere turns. The number of ampere turns in a coil is obtained by multiplying the number of amperes flowing through the coil by the number of turns of wire composing it.
FIG. 3.—By forming the wire into several loops or a spiral so that the effect of the individual turns is concentrated in a small space, an Electromagnet is made.
You can easily see the effect of turns of wire on an electromagnet by winding two or three turns of wire around a nail and connecting it to a battery. These two or three turns will probably create enough magnetism to enable the nail to lift up one or two ordinary carpet tacks.
FIG 4—The strength of an electromagnet is proportional to the ampere turns. The magnet illustrated above does not possess sufficient turns to be very strong.
Then increase the number of turns to forty or fifty and note that the magnetism of the nail has increased greatly and that it now possesses power to pick up a larger number of tacks at a time.