Consider the following statements: Assertion: Single-phase induction motor is not self-starting. Reason: Net rotating magnetic field produced by single-phase winding at standstill is zero. Of these statements:
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Answer & Explanation
Correct AnswerA. Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
Quick Explanation
At standstill a single-phase stator field can be resolved into equal forward and backward rotating fields. Their starting torques are equal and opposite, giving zero net starting torque; hence the motor is not self-starting. Both assertion and reason are true and the reason correctly explains the assertion: option A.
Formula / Key Relation
At standstill: Tf=Tb in opposite directions → Tnet=0
Detailed Explanation
Correct Answer
A — Both Assertion and Reason are true and Reason is the correct explanation of Assertion.
Concept and Reasoning
At standstill a single-phase stator field can be resolved into equal forward and backward rotating fields. Their starting torques are equal and opposite, giving zero net starting torque; hence the motor is not self-starting. Both assertion and reason are true and the reason correctly explains the assertion: option A.
Calculation / Key Relation
At standstill: Tf=Tb in opposite directions → Tnet=0
Exam Takeaway
Single-phase induction motor needs an auxiliary starting means because forward/backward torques cancel at rest.
Common Mistake
After the rotor starts, the two slips differ and the torques no longer cancel.
Quick Trick
Single-phase induction motor needs an auxiliary starting means because forward/backward torques cancel at rest.
Common Mistake
After the rotor starts, the two slips differ and the torques no longer cancel.
Exam Tip
Single-phase induction motor needs an auxiliary starting means because forward/backward torques cancel at rest.
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