assignement of a.c generator
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illustrates the construction of a simple form of a.c. dynamo for the continuous production of electric current by electromagnetic induction. The machine has a rectangular coil of wire which is rotated in the magnetic field between the poles of
a U-shaped permanent magnet. This magnet is called the field magnet. The ends of the coil are connected to two slip rings mounted on the coil spindle. Current may be obtained from the coil through two carbon brushes, which are made to press lightly against the slip rings.
The simple alternating current generator
The simple alternating current generator
As the coil rotates its sides cut the magnetic flux, and therefore a current is induced in it. Application of Fleming’s right-hand rule indicates that the current flows from back to front along side A and from front to back along side B. When viewed from above the current therefore flows in a clockwise direction round the coil.
Fig. 43.16 shows graphically how the electromotive force generated in the coil varies
The simple alternating current generator
The simple alternating current generator
over one complete rotation. As a starting-point, consider the instant that the coil is in the vertical position with its side A uppermost (Fig. 43.l6 (a». In this position the sides of the coil are moving along the magnetic flux. No cutting of flux is taking place, and therefore the e.m.f. generated at this instant is zero. During the first quarter of a rotation the e.m.f. increases from zero to a maximum or peak value when the coil is in the horizontal position (Fig. 43.l6 (b». After this the e.mJ. decreases again during the second quarter of the rotation, and once more becomes zero when the coil is in the vertical position with side B uppermost (Fig. 43.16 (c». During the second half of the rotation the e.m.f. generated follows the same pattern as that in the first half, except that the direction of the e.m.f. is reversed. This reversal occurs, since the direction of motion of the sides sides A and B across the magnetic flux is now reversed (Fig. 43.16 (d».
If this alternating e.m.f. is applied to an external resistance R an alternating current (a. c.) will flow through it.