Correct AnswerB. Ward-Leonard method
Quick Explanation
Speed magnitude can be varied by armature-voltage/field control, while direction reversal requires reversing either armature current or field flux (but not both). The control arrangement in option B provides speed control in both rotational directions.
Detailed Explanation
Correct Answer
B — Ward-Leonard method
Concept and Reasoning
Speed magnitude can be varied by armature-voltage/field control, while direction reversal requires reversing either armature current or field flux (but not both). The control arrangement in option B provides speed control in both rotational directions.
Calculation / Key Relation
T∝ΦIa
reverse either Φ or Ia → reverse torque/direction
Exam Takeaway
To reverse a DC motor, reverse one of armature or field polarity—not both.
Common Mistake
Reversing both armature and field leaves torque direction unchanged.
