A DC drive controls the ___ of a DC motor by varying the voltage applied to the armature.

A DC drive controls the ___ of a DC motor by varying the voltage applied to the armature.

• A. Torque
• B. Rotational Speed
• C. Power
• D. Current

Answer: (B)

The main idea is that a DC drive regulates how fast the motor turns by changing the voltage applied to the armature. When you raise the armature voltage, the motor speed increases because the back-EMF opposing the applied voltage increases until a steady speed is reached where the net voltage balances losses. Torque, while related, is driven mainly by the armature current (and field flux); with the field constant, torque ∝ current. So adjusting armature voltage is the way to set speed, while current controls torque. Power (voltage times current) varies with both but is not the direct control variable.

The main idea is that a DC drive regulates how fast the motor turns by changing the voltage applied to the armature. When you raise the armature voltage, the motor speed increases because the back-EMF opposing the applied voltage increases until a steady speed is reached where the net voltage balances losses. Torque, while related, is driven mainly by the armature current (and field flux); with the field constant, torque ∝ current. So adjusting armature voltage is the way to set speed, while current controls torque. Power (voltage times current) varies with both but is not the direct control variable.