Twentieth century hand-book for steam engineers and electricians, with questions and answers .. . nsider the elemental sketch of adynamo, Fig. 17. The wire a represents the armatureand we have also the iron bar and the coil of wirewound on it and, for the present, we may consider thebattery B as the source of the current which producesthe magnetism or lines of force in the iron bar. Thebattery current magnetizes the iron bar (which indynamos is known as the field magnet) and producesthe lines of force indicated by arrows. These lines of force leave the field magnet of ourdynamo at the north po
Twentieth century hand-book for steam engineers and electricians, with questions and answers .. . nsider the elemental sketch of adynamo, Fig. 17. The wire a represents the armatureand we have also the iron bar and the coil of wirewound on it and, for the present, we may consider thebattery B as the source of the current which producesthe magnetism or lines of force in the iron bar. Thebattery current magnetizes the iron bar (which indynamos is known as the field magnet) and producesthe lines of force indicated by arrows. These lines of force leave the field magnet of ourdynamo at the north pole marked N, and pass throughthe air-gap and armature into the south pole marked S. ELECTRICITY FOR ENGINEERS 43 As we begin to move the wire or armature, it cutsthrough these lines of force and begins to generate anelectromotive force, which in turn will cause the cur-rent to flow if the circuit is ciosed through a lamp orother device. This current reverses in direction as the wire a passesfrom the influence of the south pole into that of thenorth pole and the brushes B and B, which transmit. FIGURE 17. the current to the outside wires, are so set that theychange the connection of the wire a at the time that itpasses from one pole to the other. By this means thecurrent in the external circuit is kept constant indirection, although it alternates in the armature. The faster we turn our wire or armature, the greaterwill be the electromotive force generated. Instead ofusing onlv one wire, as in Fig. 17, we may take many 44 ELECTRICITY FOR ENGINEERS turns before bringing the end out, and in so doingobtain the well known drum armature, or, by a slightlydifferent method of winding, the gramme ring arma-ture, Fig. 18. Here we have many wires cutting thelines of force at once and our electromotive force withthe same number of revolutions of the armature is cor-respondingly increased, and the more turns of wire wearrange to cut those lines of force per second thegreater will be our E. M
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