What is the effect of a magnet in iron filings?

Compass

A compass is simply a thin magnet or magnetized iron needle balanced on a pivot. It can be used to detect small magnetic fields. The needle will rotate to point toward the opposite pole of a magnet. It can be very sensitive to small magnetic fields.

Using a compass to show the magnetic field

When you bring a compass near an item suspected of being magnetized or having a magnetic field, the compass will turn and point toward the appropriate pole of the object.

[img src="www.school-for-champions.com/science/images/magnetic_detecti" alt="Compass needle attracted to magnet's N pole" width="350" height="200">

A famous experiment showed that a wire with DC electric current running through it created a magnetic field. When the electricity was turned on, a nearby compass moved to indicate a magnetic field was present.

Earth is a huge magnet

The compass was used to discover that the Earth is a huge magnet. The North-seeking pole of the compass needle will always point toward the Earth's North magnetic pole.