Part 11 (1/2)

To explain this, study Fig 102, in which is a bar net (A) If we take a metal wire (B) and bend it in the for blocks, the wire netic field When this takes place, the wire receives a charge of electricity, which moves, say, in the direction of the darts, and will make a complete circuit if the ends of the looped wire are joined, as shown by the conductor (D)

ACTION OF THE MAGNETIZED WIRE--You will remember, also that we have pointed out hohen a current passes over a wire, it has aout around it at all points, so that while it is passing through the net (A), it beconet of its own and tries to set up in business for itself as a generator of electricity But when the loop leaves the netic or electrical impulse in the wire also leaves it

THE MOVEMENT OF A CURRENT IN A CHARGED WIRE--Your attention is directed, also, to another statement, heretofore ed wire passes by induction to a wire across space, so as to charge it with an electric current, it ed wire in a direction opposite to that of the current in the charging wire

Now, the darts show the direction in which the current netic field But the netic field, the current in the loop surges back in the opposite direction, and when the loop has netic field, it e the direction of flow in the current, and thus produce alternations in the flow thereof

Let us illustrate this by showing the four positions of the revolving loop In Fig 103 the loop (B) is in theupwardly in the direction of the curved dart (A), and while in that position the voltage, or the electrical impulse, is the most intense The current used flows in the direction of the darts (C) or to the left

In Fig 104, the loop (A) has gone beyond the influence of the netic field, and now the current in the loop tries to return, or reverse itself, as shown by the dart (D) It is a reaction that causes the current to die out, so that when the loop has reached the point farthest fro 105, there is no current in the loop, or, if there is any, it moves faintly in the direction of the dart (E)

[Illustration: _Figs 103-106_ ILlustRATING ALTERNATIONS]

CURRENT REVERSING ITSELF--When the loop reaches its lowest point (Fig

106) it again conetic field and the current coinal direction, as shown by darts (C)

SELF-INDUCTION--This tendency of a current to reverse itself, under the conditions cited, is called self-induction, or inductance, and it would be well to keep this incurrents

You will see froe of direction of the current, depends upon the speed of rotation of the loop past the end of the s 107-108_ FORM FOR INCREASING ALTERNATIONS]

Instead, therefore, of using a single loop, we

107), which at the saive four alternations, instead of one, and still further, to increase the periods of alternation, we108 By having a sufficient nunets, thereperiods in each second Ti currents

Let us now illustrate thethe dyna 109, the loop (A) shows, for convenience, a pair of bearings (B) A contact finger (C) rests on each, and to these the circuit wire (D) is attached Do not confuse these contact fingers with the commutator brushes, shown in the direct-currentcontact between the revolving loop (A) and stationary wire (D)

[Illustration: _Fig 109_ CONNECTION OF ALTERNATING DYNAMO ARMATURE]

BRUSHES IN A DIRECT-CURRENT DYNAMO--The object of the brushes in the direct-current dynamo, in connection with a commutator, is to convert this _inductance_ of the wire, or this effort to reverse itself into a current which will go in one direction all the time, and not in both directions alternately

To explain this s 110 and 111

Let A represent the arrooves (B) for the wires

The co insulated fro 110, the upper one, we shall call and designate the positive (+) and the lower one the negative (-) The armature wire (C) has one end attached to the positive commutator terative ter 110_ DIRECT CURRENT DYNAMO]

One brush (D) contacts with the positive terative terminal Let us assume that the current impulse imparted to the wire (C) is in the direction of the dart (F, Fig 110) The current will then flow through the positive (+) terminal of the coh the wire (G) to the brush (E), which contacts with the negative (-) terminal of the commutator This will continue to be the case, while the wire (C) is passing the netic field, and while the brush (D) is in contact with the positive (+) terminal But when the armature makes a half turn, or when it reaches that point where the brush (D) contacts with the negative (-) terminal, and the brush (E) contacts with the positive (+) terh the wire (G) takes place, unless soe it before it has reached the brushes (D, E)

[Illustration: _Fig 111_ CIRCUIT WIRES IN DIRECT CURRENT DYNAMO]

Now, this change is just exactly what has happened in the wire (C), as we have explained The current attempts to reverse itself and start out on business of its own, so to speak, with the result that when the brushes (D and E) contact with the negative and positive teroing in the direction of the dart (H)--that is, while, in Fig 110, the current flows froative terminal into the wire (C), the conditions are exactly reversed in Fig 111 Here the current in wire C flows _into_ the negative (-) terminal, and _from_ the positive (+) terminal into the wire C, so that in either case the current will flow out of the brush D and into the brush E, through the external circuit (G)

It will be seen, therefore, that in the direct-current , or back-and-forthin one direction, whereas in the alternating current no such change in direction is attempted