why the iron fillings arrange themselves in a particular pattern when sprinkled on the magnet?
Iron filings near the bar magnet align themselves along the field lines.
The magnet exerts its influence in the region surrounding it. Therefore the iron filings experience a force. The force thus exerted makes iron filings to arrange in a pattern. The region surrounding a magnet, in which the force of the magnet can be detected, is said to have a magnetic field. The lines along which the iron filings align themselves represent magnetic field lines.