Figure above shows the illustration of a simple direct current (d.c.) generator.
You should notice that the simple d.c generator is almost the same as the d.c. motor except that the battery in the d.c. motor is removed and replaced by a resistor.
The direct current generator produces electric current (or voltage) base on the principle of electromagnetic induction.
Figure below shows the change of the induced voltage when the coil is at different postion.
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.
