GCSE revision: why I think transformers are odd!

I remember once showing this to a class and they were underwhelmed. They said "we press switches every day and lights come on, sir". But what makes me think it is odd is that both coil A and coil B have insulated wires. Even though the core around which they are both wrapped is of iron, there is no way the current can get out of one wire and flow through to the other wire. Coil A is an electromagnet. The squiggly line is an a.c. power supply. That means that the poles of the electromagnet keep changing direction. This changing magnetic flux then waggles backwards and forwards in coil B because the flux can travel to coil B through the iron. As pointed out yesterday, waggling a magnet inside a coil produces induced electricity - that's what causes the bulb to light. We also showed that coils with fewer turns had a smaller induced voltage. That's how a step down transformer works.