Dot convention meaning

Question

I have two questions about dot convention for the ideal transformer. I have understood how to use them in writing the voltage drops on the coils, but I have some doubts:

1) Which is the physical cause of their necessity? Intuitively, I think it is due to the fact that the direction of the magnetic field generated by a coil connected to a voltage source depends not only on how it is connected to it, but also on its winding sense.

2) If we write the ideal transformer equation: V2/V1 = I1/I2, do we apply the dot convention as we do for evaluating the voltage drops on the coils?

If it is true, we would write for instance:

V2/V1 = - I1 / I2

for the following scheme, since I1 flows in the dot and then in the inductor, and I2 the opposite.

Answer 1

Reality is this - if you apply a voltage source to the primary of a transformer then the phase difference between primary voltage (dot end) and secondary voltage (dot end) is zero. In other words the dots tell you about the phase relationship between primary wires and secondary wires.

Because of this, if you have a load resistor connected to the secondary, load current flowing into the dotted primary wire is matched by a secondary current flowing out of its dotted secondary wire. This of course is a 180 degrees shift.

The above analysis ignores magnetization current.