Question

When we sprinkle iron filings on a paper on which a bar magnet is kept, why do the iron filings spread in the shape of the magnetic field lines and why don't they all stick to the magnet?

Answer 1

The iron filings take up a definite pattern (curved lines).

This happens because each piece of iron filing becomes a magnet to the magnetic induction of the magnet. It thus experiences a force in the direction of the magnetic field of the bar magnet at that point and aligns itself along curved lines which are the magnetic field lines.