Bar magnet is an object that has a magnetic field. They have distinct North & South poles. They are not very strong but that makes them ideal for showing magnetic field lines when used with iron filings. If they were much stronger, the filings would clump & not show anything useful. In a bar magnet the magnetic field lines go from the northern end of the magnet and return at the southern end. The lines of magnetic field from a bar magnet form closed lines. The magnetic field of a bar magnet can be investigated with a compass needlel.