The magnetic field of a bar magnet can be investigated with a compass needle. The magnetic poles of both bar magnet and compass needle are symbolized by the following colours:
If you move the magnetic needle with pressed mouse button, the magnetic field line through the center of the compass needle will be drawn with blue colour. The blue arrows mark the direction of the magnetic field which is defined as the direction indicated by the north pole of the compass needle. If you turn the magnet by using the red button, the direction of the field lines will reverse. The other button makes it possible to clear all field lines.