What do compasses work by reacting to?

Compasses operate based on magnetic fields. The needle of a compass is a small magnet that aligns itself with the Earth's magnetic field. This magnetic field is generated by the movement of molten iron within the Earth's outer core, producing magnetic lines of force that extend from the magnetic south to the magnetic north. When you hold a compass, the needle rotates freely and points toward the magnetic north, allowing you to determine your direction relative to the Earth's magnetic poles.

This principle is fundamental to navigation, as the magnetic field provides a consistent reference point for orientation. The other choices—electric fields, light waves, and sound waves—do not play a role in the compass's functionality, as they do not interact with the magnetic properties of the needle in the same way that magnetic fields do.