Current in secondary coil as current in primary increases

[TT0]

Hi, so the scenario is that the primary coil of a transformer is attached to a battery in a circuit with a variable resistor. The resistor is set to the maximum resistance.

As I increase the current in primary coil by reducing resistance at a constant rate, will the current in the secondary also slowly increase? Since as current increase, flux increases, and the secondary coil will oppose this increase in flux by inducing flux in opposite direction by increasing current in the secondary coil (Lenz's law). However, faraday's law is that emf is equal to the change in flux, so that means the secondary coil should have a constant current. What is the problem with my understanding of transformers?

Thanks

 

[cnh1995]

As I increase the current in primary coil by reducing resistance at a constant rate,

You can't do that with the secondary circuit closed. Current in the primary will no longer depend only on the change in resistance. It will also depend on the secondary resistance. The two circuits are now magnetically coupled and you'll have to consider how they affect each other (at the same time).

Even if the secondary were open, you can't increase the primary current at a constant rate by reducing the resistance at a constant rate because of its magnetizing inductance (very large).

Best way to understand what happens in a circuit like this is to write the differential equation of KVL for primary and secondary and solve it.

 

[sophiecentaur]

If you attach a transformer to a battery there will be a single pulse of induced emf in the secondary and then DC current through the primary.

Hi, so the scenario is that the primary coil of a transformer is attached to a battery in a circuit with a variable resistor. The resistor is set to the maximum resistance.

As I increase the current in primary coil by reducing resistance at a constant rate, will the current in the secondary also slowly increase? Since as current increase, flux increases, and the secondary coil will oppose this increase in flux by inducing flux in opposite direction by increasing current in the secondary coil (Lenz's law). However, faraday's law is that emf is equal to the change in flux, so that means the secondary coil should have a constant current. What is the problem with my understanding of transformers?

Thanks

If you increase the primary current at a constant rate, the secondary emf will be constant. So the secondary current (into a resistive load) will be constant, too.
This process has to end somewhere - when the input power supply runs out of Volts, of course.

 

[TT0]

Thanks