To reverse the direction of rotation of a DC motor, you should...

To reverse the direction of rotation of a DC motor, you should...

• A. Reverse both the armature and the field.
• B. Reverse the polarity of the armature or the field, but not both.
• C. Reverse only the supply voltage.
• D. Reverse the rotor's mechanical connection.

Answer: (B)

DC motor rotation is determined by the direction of current in the armature relative to the magnetic field produced by the windings. The torque that drives rotation depends on the relative direction of these two; reversing one while keeping the other fixed reverses the torque and thus the rotation. So, if you reverse the polarity of the armature, or you reverse the polarity of the field winding, you flip the torque direction and the motor spins the opposite way. If you reverse both the armature and the field at the same time, the relative directions stay the same, so the rotation does not change. Reversing only the supply voltage isn’t a reliable general method because it can affect the armature and field in different ways depending on how the motor windings are wired (series, shunt, or separately excited). Reversing the rotor’s mechanical connection isn’t a practical method to change electrical rotation direction.

DC motor rotation is determined by the direction of current in the armature relative to the magnetic field produced by the windings. The torque that drives rotation depends on the relative direction of these two; reversing one while keeping the other fixed reverses the torque and thus the rotation.

So, if you reverse the polarity of the armature, or you reverse the polarity of the field winding, you flip the torque direction and the motor spins the opposite way. If you reverse both the armature and the field at the same time, the relative directions stay the same, so the rotation does not change. Reversing only the supply voltage isn’t a reliable general method because it can affect the armature and field in different ways depending on how the motor windings are wired (series, shunt, or separately excited). Reversing the rotor’s mechanical connection isn’t a practical method to change electrical rotation direction.