I came across this problem: Explain how you would determine which was the north pole of a bar magnet, without using any other magnet. I was thinking of using a solenoid, and dropping the magnet in. Then you can determine whether it was a north or south pole by whether the current flows clockwise or anticlockwise. I was thinking that one of these would produce a negative current, but I am not sure which. Is there any way to do this?