What is a magnetic field?
Magnetic objects generate magnetic fields, which can be illustrated by magnetic field lines and made visible with the help of a compass needle or iron filings. Experiments like these are familiar to most from physics or chemistry classes.
The field lines of a magnetic object have neither beginning nor end and run differently depending on each magnet. The strength of a magnetic field also decreases with increasing distance - this reduction can be calculated mathematically and also varies from magnet to magnet.