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Let's say we have an ideal transformer with a diode in the secondary circuit:

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If the diode is reverse biased, there would be no current in the secondary circuit, which would mean that there is no power consumed in the secondary circuit. How would that affect the current in the primary circuit?

My teacher says that the current would be zero in the primary circuit too, since the power consumed in the primary and secondary circuits are equal, and hence the power in the primary circuit is zero, which means that the current flowing in it would be zero.

Is this correct? I know that the primary circuit is connected to an alternating voltage source and that the circuit is closed; thus, the source should produce a current in the primary circuit independent of the secondary circuit. How can the current possibly be zero?

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  • $\begingroup$ I don't know about your diagram, but I can tell you what would happen if you replace the diode with a switch. The current waveform in the primary would be about the same magnitude regardless of whether the switch was open or closed, but operating the switch would shift the phase of the current waveform. With the switch open, the current would be ninety degrees out-of-phase with respect to the voltage. The primary would draw power from the grid for part if its cycle, and it would feed power back to the grid for the other part, and the net effect would be close to zero average power. $\endgroup$
    – Solomon Slow
    Commented May 15, 2022 at 14:02
  • $\begingroup$ @SolomonSlow I'm a little confused. So closing the secondary circuit changes the phase of current in primary circuit? (I'm in high school and what we've dealt with is changing emf across the inductor in primary , by mutual inductance would result in an change in emf across the secondary , but the other way around is a little hard for me to wrap my head around. ) $\endgroup$
    – jen
    Commented May 15, 2022 at 14:26
  • $\begingroup$ A transformer is two (or more) inductors that are magnetically coupled to each other. Current flow in each inductor, voltage in each inductor, and the magnetic flux in the core all are interconnected. In the special case where only one winding of the transformer is connected to anything, then that winding behaves like a simple inductor. An ideal inductor* can not dissipate any energy: It only stores energy and gives it back later. [* But, real inductors can be pretty far from ideal.] $\endgroup$
    – Solomon Slow
    Commented May 15, 2022 at 14:45
  • $\begingroup$ I've learnt about inductors, inductive circuits and alternating currents.(I realize I might have omitted the word "inductor" at a few places). But my book doesn't explain phase changes of currents in the primary and secondary circuit,(for transformers, we just learnt that power in primary= power in secondary) and also for mutual inductance, we simply derive the formula for two linked solenoids and nothing more was discussed. Could you please recommend a resource that deals with these in more detail? $\endgroup$
    – jen
    Commented May 15, 2022 at 15:07

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