Kim west, age 11, of Calgary, Alta., Canada, for her question:
What is an armature?
Sometimes a word is so useful it may have several different duties. A wire may be a thread of metal or a telegram. Armature is another one of these useful words. It has a meaning for the zoologist and another for the botanist. It has a special meaning for the soldier and another for the electrician.
The basic meaning of the word armature concerns armor. Crash helmets and other shields that protect the body may be called armatures. We tend to borrow useful words to name similar things in other fields. The protective thorn on a rose bush is an armature, and so is the tooth of a tiger. A cable wound around with coils of wire is called an armature, maybe because its metal covering resembles the meshwork of ancient body armor.
The last meaning of armature was borrowed by the electric dynamo. It is the name of an object that is at the heart of the dynamos and generators that create our electric power. As far as our daily lives are concerned, this armature is the most useful of all.
We must know something of the miraculous process called electromagnetic induction in order to understand what it is. These grand words are hard to understand, even for an expert in electronics. In fact, he cannot tell you why electromagnetic induction works to create electric current, but he certainly can tell you how it works.
Long ago Michael Faraday discovered how to create an electric current by turning a handle. Current was made by chemical means before that. Faraday made a little dynamo to create current by mechanical means. It was a simple copper disk set between the two prongs of a horseshoe magnet. This gadget was linked to the two ends of a loop of copper wire. The magnet was surrounded by its invisible magnetic field, and there was a handle to turn the disk and make it cut through the magnetic field again and again.
This magic trick was called eiectromagnetic induction. It caused a current to flow through the circuit of copper wire. Our generators use the same trick on a grand scale. Faraday's little copper disk became a massive core of iron or steel wound in a metal coating of copper coils. This is the armature of a generator. When a mighty magnet swings around and around it, the generator creates alternating current. In a dynamo, the armature turns through a magnetic field and creates direct current.
Both the generator and the dynamo are descended from faraday's first litt1e gadget that had a mechanical crank to create electric current.. Both have magnets to provide immense magnetic fields and massive armatures wound with copper coils. Current is created when the armature cuts again and again through the magnetic field. The armature may spin through the field or the magnet may spin its field around the armature.