I have answered your other questions on PHF
4. I'm not sure about this one, but if you have a current carrying conductor and a compass needle, you will see that as soon as current flows, if the compass needle is near to the wire, the needle will be deflected.
This is due to electromagnetism, which I don't quite understand to be honest.
I found this article: Maxwell's equations - Wikipedia, the free encyclopedia
Apparently, there is the answer somewhere, but right now, I'm sort of short on time to read this all...