Generator can be modified to an a.c generator by replacing its commutators with two (separate) slip rings. The two slip rings rotate in tandem with the armature. Carbon brushes connect the armature to the external circuit. The armature is initially at the vertical position. No magnetic flux is cut and hence no induced current exists.
When the armature rotates, the change in magnetic flux increases and the induced current increases until its maximum value at the horizontal position. The direction of the induced current can be determined from Fleming's Right Hand rule.
As the armature continues on its rotation, the change in magnetic flux decreases until at the vertical position, no induced current exists.
Subsequently upon reaching the horizontal position again, the induced current is maximum, but the direction of the induced current flowing through the external circuit is reversed.
The direction of the induced current (which flows through the external circuit) keeps changing depending on the orientation of the armature. This induced current is also known as alternating current. The current is positive (+) in one direction and negative in the other (-). The smooth rings play a critical role in the generation of alternating current.
Physics Animation
Applet
AC and DC Generator - Walter Fendt
AC Generator - Molecular Expression
A simple d.c generator essentially the converse of a d.c. motor with its battery removed.
Initially the armature is vertical. No cutting of magnetic flux occurs and hence induced current does not exist. When the armature rotates, the change in flux increases and the induced current correspondingly increases in magnitude. After rotating by 90°, the armature is in the horizontal position. The change in magnetic flux is maximum and hence the maximum induced e.m.f is produced. Maximum induced current flows through the galvanometer.
When the armature continues to rotate, the change in flux decreases. At the 180° position, there is no change in flux hence no induced current exists.The induced current is achieves its maximum value again when the armature is at 270°. After rotating 360°, the armature returns to its original position.
The direction of the induced current can be determined from Fleming's Right-Hand Rule. Even though the magnitude of the induced current or d.g.e is dependent on the orientation of the coil, the current in the external circuit always flows in one direction. This uni-directional current is known as direct current.
Physics Animation
Applet
DC Generator - Molecular Expression
