MM0704, Lesson 3
Figure 3-4. Current-Carrying Conditions in a Magnetic Field.
is suspended in a magnetic field, as shown in figure 3-5A, a zero torque (turning effect) is exerted on the coil. The
forces acting on the coil sides tend to separate them. In figure 3-5B, the forces acting on the coil sides produce a torque
which reaches its maximum at position in figure 3-5C. If the current in the coil were reversed at the proper moment, a
continuous rotating force would be developed. This current is changed by a commutator. If this simple coil is in the
zero-torque position when the current is connected, it will not start.
Figure 3-5. DC Motor, Showing Positions on the Current-Carrying Coil.