From the instant of start-up, through the acceleration period, and until the motor reaches rated speed, when is the counter EMF produced in the windings of a DC motor "zero"?
• Counter EMF (CEMF) depends on armature rotation and magnetic field strength • How CEMF changes from start-up, through acceleration, to rated speed in a DC motor • The relationship between armature speed and the magnitude of induced voltage in the windings
• At what exact moment during start-up and acceleration is there no motion to cut the magnetic field lines? • How does the induced counter EMF compare to the applied voltage when the motor is stopped, just starting to move, and at full speed? • Which choice describes a condition where the induced voltage in the armature windings must still be exactly zero?
• Identify when the armature speed is exactly zero • Determine whether any rotation at all produces some non‑zero CEMF • Confirm that CEMF is proportional to armature speed in a DC motor
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