When I was a child, I brought a nail (metal bar) and I made some turns around the nail. It was something like a coil and the nail was the core of that coil. When I applied DC on the coil using 1.5 V battery, the nail had become a magnet. It was attracting other nails and metals.
Now, I've learned that the magnetic field is generated due to change of current in a wire, and that's why we apply AC to transformers and coils.
I have two questions:
Why the nail is magnetized although there is no changes in current (DC) ?
Why we don't apply DC to transformers and coils ?