Which end of an electromagnet is north?
Without using a compass, there is a simple way of finding which is the north pole or south pole of an electromagnet.
Turn the electromagnet so that the end faces your eye. If the electricity travels clockwise around the electromagnet then the end you are looking at is the south pole. If the electricity travels anticlockwise around the electromagnet then the end you are looking at is a north pole.
This is summarised by the following pictures:
If we draw out each of the possible configurations, you can see the polarity of each.
The difference between the two images above is that the wire has been wound the opposite way in the second one, changing the direction in which the electrical current travels, and therefore changing the polarity.
Below, the images are repeated, the only difference being that the battery has been reversed to change the direction of the current, and therefore the polarity.