On a nanoscopic level, what really happens to the electrons in the secondary coil of a step-up transformer? I know that when AC is passed through the primary coil of a step-up transformer a higher emf is induced in the secondary coil (with more turns) of the transformer. Since energy is conserved, and P = VI, this would mean a drop in current. But I'm not able to visualize what is really happening to the electrons in the secondary coil. Does a higher voltage in the secondary coil mean that all electrons in the secondary coil are taken to a higher potential? And why is the current (flow of electrons) low when that happens?
What is really happening to the charges in the secondary coil?
 A: Sorry for my poor english. French is my native language.
I don't think it is necessary to go to the microscopic level. it would be very complicated to study the radiation of electrons at this level !
Maybe it's more natural to reverse the reasoning by asking why the primary current increases when current flows in the secondary coil ?
Imagine a transformer with the secondary coil in an open circuit: the current delivered by the secondary coil is zero. So, the current at the primary is very low (ideally zero) because the impedance of the primary circuit is very high (ideally zero if the permeability is infinite).
Now place a resistor at the secondary coil : current will flow under the effect of the induced emf. Why is the primary current going to increase?  because the current flowing in the secondary coil will generate a flux through the primary coil. The generator supplying the primary coil no longer simply "sees" the input impedance of the single coil. The induced emf will modify this input impedance. The calculation shows that this leads to an increase in the current at the primary. And we understand this well by using the conservation of energy.
A: What happens in the primary coil
Electrons whose motion is forced into curved paths align their magnetic dipoles (and yes, each electron is also a tiny magnet). The core of the transformer directs this common magnetic field through the secondary coil.
What happens in the secondary coil
In the case that the magnetic field changes, the electrons in the secondary coil are aligned by this field and experience a shift (Lorentz force, Hall effect). Since for all electrons the magnetic dipole and the spin are related, all electrons are shifted in the same direction (an empirical fact that allows us to use inductive processes in everyday life).

Does a higher voltage in the secondary coil mean that all electrons in the secondary coil are taken to a higher potential?

In the secondary coil, the changing magnetic field induces electron displacement along the entire wire. If the length of the wire is short in relation to the primary coil, more electrons can be shifted per mm and this leads to a higher current. Since the power of the (ideal) transformer must be the same on both sides, the voltage on the second coil must be lower.
If on the other hand the secondary coil has more turns, fewer electrons per unit length can be displaced; the current is lower and the voltage higher.

And why is the current (flow of electrons) low when that happens?

The power on both sides of the transformer must be the same (without taking power losses into account). The power is the product of current and voltage P = U*I. If more electrons are affected in the secondary coil (higher current), the voltage is lower and vis-a-vis.
