Hello, I am learning about transformers and how if you have an Open-Circuit on the Secondary side of the transformer than there is no current flow. But when you connect a Load to the secondary side completing the circuit then i read:

"The secondary current, IS which is determined by the characteristics of the load, creates a self-induced secondary magnetic field, ΦS in the transformer core which flows in the exact opposite direction to the main primary field, ΦP. These two magnetic fields oppose each other resulting in a combined magnetic field of less magnetic strength than the single field produced by the primary winding alone when the secondary circuit was open circuited. "

I drew the image above that i copied from this website here to visualize how the two current flow opposite of each other.
My Questions,
1) What does it mean when they say ""The secondary current, IS which is determined by the characteristics of the load, creates a self-induced secondary magnetic field", Can someone explain in an easy to understand way how it creates a self- induced secondary magnetic field?
2) What is it exactly about connecting a load that causes it to flow current in the direction opposite that of the primary?

 

1. The voltage waveform across the primary causes a similar waveform to be induced across the secondary. The secondary voltage acting on the load results in current flowing. Changing the load changes the current drawn by it. For example if a resistor, you get current in phase with the voltage and if it is an inductor you get current that lags the voltage by 90°.

2. If the secondary current generated flux in phase with the input there would be no "feedback" to the primary to cause the load current to be shown in the primary. See this Wikipedia entry: https://en.wikipedia.org/wiki/Lorentz_force

A. You also have magnetizing current flowing in the primary regardless of whether a load is connected to it or not. For the most part it is voltage divided by the reactance of the primary, and another significant effect is that imperfect coupling between the primary and secondary gives rise to leakage inductance.