re: HSC Physics Marathon Archive
For DC motors, a changing flux caused by relative motion between an external magnetic field and the motor coils will induce an EMF induces a current that creates a magnetic field to oppose the change that caused it in the first place. In contrast, a changing flux for A.C. induction motors will induce an EMF that creates a current to support the motion of the rotor (torque created by the induced current is in the same direction as the "rotating" magnetic field).
For DC motors, the induced EMF will effectively travel in a single direction (due to S.R.Cs). For A.C induction motors, multiple sets of opposing stator coils (usually 3 phase) will induce EMF in an alternating direction.
The induced EMF in D.C. motors is caused by the rotation of the rotor coils through an external magnetic field. For A.C. induction motors, the induced current is caused by the "alternating" magnetic field of the stator.
