126. The Dynamo, Dynamo-Electric Machine or Generator, is a machine for converting mechanical energy into an electric current, through electromagnetic induction. The dynamo is a machine that will convert steam power, for example, into an electric current. Strictly speaking, a dynamo creates electrical pressure, or electromotive force, and not electricity, just as a force-pump creates water-pressure, and not water. They are generally run by steam or water power.
Fig. 137.
127. Induced Currents. We have already spoken about currents being induced by moving a coil of wire in a magnetic field. We shall now see how this principle is used in the dynamo which is a generator of induced currents.
Fig. 138.
Fig. 137 shows how a current can be generated by a bar magnet and a coil of wire. Fig. 138 shows how a current can be generated by a horseshoe magnet and a coil of wire having an iron core. The ends of the coil are to be connected to an astatic galvanoscope; this forms a closed circuit. The coil may be moved past the magnet, or the magnet past the coil.
| Fig. 139. | Fig. 140. |
| Fig. 141. | Fig. 142. |
Fig. 139 shows how a current can be generated by two coils, H being connected to an astatic galvanoscope and E to a battery. By suddenly bringing E toward H or the core of E past that of H, a current is produced. We have in this arrangement the main features of a dynamo. We can reverse the operation, holding E in one position and moving H rapidly toward it. In this case H would represent the armature and E the field-magnet. When H is moved toward E, the induced current in H flows in one direction, and when H is suddenly withdrawn from E the current is reversed in H. (See "Study," Chapter XXV., for experiments.)
