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MANAGERS AND PROJECTIONISTS
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be induced or generated in wire B, and if wire A and B form complete circuits, current will flow in B.
A transformer depends for its action on this principle, supplemented by the following: When the switch is closed, charging the primary coil in Fig. 197 with alternating E. M. F., the wires thereof instantly become surrounded by lines of magnetic force, as shown in Fig. 198, and these lines of force acting on the iron core create a magnetic field of great intensity. This causes the primary coil to become in effect a choke coil of such power that unless current be taken from the secondary, and power be thus consumed, no wattage at all will be consumed in the primary coil. Electro motive force and current is generated in the secondary coil, which is immersed in the magnetic field created by the primary coil, because the magnetic field is in fact a magnetic circuit, its lines of magnetic force flowing in a fixed path through the air from the north pole to the south pole of the field.
Reverting back to "H o w Electricity Is Generated," Page 6, we find that electricity is generated in the armature of a dynamo because the wires cut across the lines of magnetic force which constitute the magnetic field. In a transformer the same identical thing is true in reverse. Current is generated in the secondary coil by reason of the fact that, instead of the wires themselves moving and cutting lines of force, the flow of magnetic energy "cuts" or passes across the wires, which amounts to exactly the same thing as the wires cutting through or across the lines of magnetic force, hence a current of electricity, called the secondary current, is generated or "induced" in the secondary coil. This secondary current is termed an "induced" current.
The action of a transformer is entirely automatic. The primary current creates a magnetic field which, as already explained, generates or ''induces" a current in the secondary coil. This latter current also sets up a magnetic field, but its magnetic flow is in a direction opposite to the flow of the primary field. It therefore follows that when the secondary current flow is increased or decreased, the relative strength of the two magnetic fields (primary and secondary) is
Figure 198.