Cutting Lines of Force.—The loop will now be turned to the right so that it passes the magnetic field and goes beyond it in its revolution. This motion of passing the armature through the magnetic field is called cutting the lines of force. While the loop was lying within the magnetic field, and also when it was moving through the field, the current set up in the loop flowed in the direction of the darts F, or to the right, through the pivots D.
In [Fig. 43] the loop is shown as having made a quarter turn, and it is now vertical, or at right angles to its former position. The loop in thus passing away loses its force, until it reaches the position shown in [Fig. 44], when there is a surging back of the current to the opposite direction, as indicated by the arrows.
When the loop reaches the lowest position, shown in [Fig. 45], it again begins to get the influence of the magnetic field, and a reversal back to its former direction takes place, this surging movement back and forth being due to the reversal of the polarity in the coil brought about by the position in which it is placed relative to the magnetic field.
It is now an easy matter to connect the ends of the loop with wire conductors. This is shown in [Fig. 46], where a small metal wheel G is placed on each end of the spindle, and in having a strip of metal bearing H on the wheel. These are not commutator brushes, but are merely wiping brushes to take the current from the turning parts. Wires I connect with these wiping bars, and through them the current is transmitted to perform the work.
Plurality of Loops.—The dynamo may have a plurality of loops, which are called coils, and there may be a single magnet or any number of magnets. Instead of driving these coils past the face of the magnet, or magnets, the latter may be driven past the coils. In fact with most of the alternating current machines the fields are the rotating parts and the armatures, or the coils, are fixed.
The voltage is increased if the coils have a large number of turns on the armature, and also if the armature, or the turning part, is speeded up. Voltage will also be higher if larger or more powerful magnets are used in the magnetos.