#### cnh1995

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So this question was asked in GATE-2019 (EE). (GATE is the national Engineering post-graduate entrance exam in India and is conducted every year by one of the 7 top IITs (Indian Institute of Technology) and IISc Bangalore. This year, it was conducted by IIT Madras.)

The answer I found in the official answer key released by IITM is c).

Most of the "coaching institutes" for this exam had also provided c) as the correct answer in their post-exam question paper analysis.

Their reasoning was as follows:

Since flux ∝ V/f and we are reducing rms value of voltage, flux is also reduced.

Also, magnetizing inductance L

But how can magnetizing inductance change here as the magnetic coupling and self inductances of the coils remain unchanged throughout? If you reduce V 'x' times, the magnetizing current also reduces 'x' times and their ratio (X

My reasoning tells me it should be b) instead. I'll post my reasoning later, but first, I need to know whether c) is right or wrong.

Thanks in advance!

The answer I found in the official answer key released by IITM is c).

Most of the "coaching institutes" for this exam had also provided c) as the correct answer in their post-exam question paper analysis.

Their reasoning was as follows:

Since flux ∝ V/f and we are reducing rms value of voltage, flux is also reduced.

Also, magnetizing inductance L

_{m}is proprtional to the flux. Hence, magnetizing inductance will also reduce. Therefore, c) is the correct option.But how can magnetizing inductance change here as the magnetic coupling and self inductances of the coils remain unchanged throughout? If you reduce V 'x' times, the magnetizing current also reduces 'x' times and their ratio (X

_{magnetizing}) remains the same. Assuming absence of saturation and other nonidealities, isn't this simple Ohm's law in action? How can the answer be c)?My reasoning tells me it should be b) instead. I'll post my reasoning later, but first, I need to know whether c) is right or wrong.

Thanks in advance!

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