Law of Transformers: A.C Source & Induced EMFs

the law of the transformer states that
in primary coil , the EMF = -n multiplied by the rate of change of flux with respect to time
but that law applies to induced EMFs , and since the voltage in the primary coil is not actually induced but rather produced by an external source of A.C , then how can we apply the rule to such a thing ? in the secondary the voltage is purely induced so the law does apply , but in the primary coil the potential difference is not induced .

It's the same thing as in the other thread. The voltage across the primary is going to be the sum of the induced voltage and the voltage needed to drive the given current through the wire. The induced voltage works exactly the same way in both coils, but in primary it's the back EMF, while in secondary, it's EMF for whatever that coil is driving.

If it makes it simpler for you, you can always think of a real coil as a perfect, zero resistance inductor and a resistor in series. Resistor is just ohmic, giving voltage drop equal to IR, while the inductor portion gives just the induced voltage proportional to the rate of change of magnetic flux.

oh , so the inductor voltage just acts as a voltage drop , i never knew that a voltage drop was opposing the current :D thanks a lot , made lots of things clear

there is voltage drop on resistor for example and it doesn't produce a opposite current flow.It just opposes current , but that is a different thing, in a resistor the current flow produces interactions at the subatomic level which manifest themselves as heat , in the case of a back EMF a field works against the charged particle flow ,current.voltage drop isn't responsible for current reversal , in an inductor or transformer and also in electric motors , there is a phenomenon called back EMF , in other words when you add a potential difference to a coil , it causes current to flow , that current has a magnetic field around it which when changing in both magnitude and direction creates a changing electric field which opposes the original current flow magnetic field that created it.

actually member K2 answers this in your other post quite nicely.

I would like to clarify that the law of transformers applies to both primary and secondary coils, regardless of the source of the voltage. This law states that the induced electromotive force (EMF) in a coil is equal to the negative product of the number of turns in the coil (n) and the rate of change of magnetic flux with respect to time. This means that the voltage in the primary coil, whether it is induced or produced by an external source, still follows this law.

The key concept to understand here is that the law of transformers is based on Faraday's law of electromagnetic induction, which states that a changing magnetic field can induce an EMF in a closed circuit. In the case of a transformer, the changing magnetic field is created by the alternating current (AC) passing through the primary coil. This changing magnetic field then induces an EMF in the secondary coil, according to the law of transformers.

Therefore, whether the voltage in the primary coil is induced or produced by an external source, the law of transformers still applies because it is based on the fundamental principle of electromagnetic induction. The primary coil is still subject to the changing magnetic field and will still experience an induced EMF, even if it is also receiving a voltage from an external source.

In summary, the law of transformers applies to both primary and secondary coils, regardless of the source of the voltage. It is important to understand that this law is based on the principle of electromagnetic induction and is not limited to only induced voltages.