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MAGNETIC GENERATION OF ELECTRIC CURRENT 461
action periodically reverses its direction of flow. It is therefore called "alternating current."
(3) Direct current is drawn from an alternatingcurrent generator (all generator armatures create alternating current) by means of a mechanical "rectifier" called a "commutator," which is described on Page 297.
This method of generating a flow of negatrons (the negatrons are not created ; all that hapens is that motion is imparted to negatrons existing in the conductor) depends upon the fact that motion, either of the conductor or of the magnet, changes the magnetic force acting upon the negatrons. Therefore it should be possible to generate current flow without physical motion, merely by changing the strength of a magnet. This can be done with an electro-magnet, and the device that does it is called a "transformer."
The Electrical Transformer
(4) A wire carrying current is a magnet. Place another wire alongside it. Call this second wire Wire "B," and the wire carrying current Wire "A." Then we have the same condition as above, a magnet placed near a conductor. Now so long as the current flowing through Wire A remains steady and unchanged in strength, there will be no change in the influence of the magnetic field upon the negatrons in Wire B, but the moment the strength of .the current through Wire A changes, the negatrons in B take up new positions, and while in the motion of doing so they constitute an electric current.
It is obvious that the strength of the current in Wire A can only be changed either by increasing or decreasing its volume. It cannot increase in strength forever; neither can it decrease forever without reaching zero. Precisely as in the case of current generated by means of physical motion in a magnetic field, the generation of current by means of change in the strength of an electromagnet must result in change of direction of flow — in the creation of alternating current. (5) D. c. cannot be drawn from a transformer.