2-2
Figure 2-1.—Right-hand rule for motors.
To find the direction of motion of a conductor, extend the thumb, forefinger, and middle finger of
your right hand so they are at right angles to each other. If the forefinger is pointed in the direction of
magnetic flux (north to south) and the middle finger is pointed in the direction of current flow in the
conductor, the thumb will point in the direction the conductor will move.
Stated very simply, a dc motor rotates as a result of two magnetic fields interacting with each other.
The armature of a dc motor acts like an electromagnet when current flows through its coils. Since the
armature is located within the magnetic field of the field poles, these two magnetic fields interact. Like
magnetic poles repel each other, and unlike magnetic poles attract each other. As in the dc generator, the
dc motor has field poles that are stationary and an armature that turns on bearings in the space between
the field poles. The armature of a dc motor has windings on it just like the armature of a dc generator.
These windings are also connected to commutator segments. A dc motor consists of the same components
as a dc generator. In fact, most dc generators can be made to act as motors, and vice versa.
Look at the simple dc motor shown in figure 2-2. It has two field poles, one a north pole and one a
south pole. The magnetic lines of force extend across the opening between the poles from north to south.
Figure 2-2.—Dc motor armature rotation.
The armature in this simple dc motor is a single loop of wire, just as in the simple armature you
studied at the beginning of the chapter on dc generators. The loop of wire in the dc motor, however, has
