The basic difference between a d-c generator and an a-c generator is that the a-c generator uses
A. a brush.
B. two field poles.
C. a commutator.
D. two slip rings.
The correct answer and explanation is:
Correct Answer: D. two slip rings
The basic difference between a direct current (d-c) generator and an alternating current (a-c) generator lies in the method they use to collect current from the rotating coil. A d-c generator uses a commutator, while an a-c generator uses two slip rings. This distinction directly influences the type of current that each machine produces.
In an a-c generator, the armature or coil rotates within a magnetic field, producing an alternating voltage as it cuts through the lines of magnetic flux. To transfer the generated alternating current to the external circuit, the coil is connected to two slip rings. These slip rings are continuous conducting rings that rotate with the coil and maintain electrical contact with stationary brushes. The slip rings do not reverse the connection of the coil to the external circuit. As a result, the current changes direction periodically, creating an alternating current.
In contrast, a d-c generator also produces an alternating voltage within the coil. However, to convert this alternating voltage into direct current for the external circuit, a commutator is used instead of slip rings. A commutator is a split ring that reverses the connection of the coil to the external circuit every half-turn. This mechanical reversal ensures that the current always flows in one direction through the external load, resulting in direct current output.
Although both machines use similar electromagnetic principles, the key difference is in how the electrical output is collected and modified. The use of slip rings in an a-c generator maintains the natural alternating nature of the generated voltage, while the use of a commutator in a d-c generator rectifies the current mechanically to produce direct current. This difference is fundamental in understanding the applications and design of each type of generator.