Is there a simple definition or way of understanding magnetic fields?
I’m not sure there’s any ultra-simple global definition, but some basic properties of magnetic fields are not hard to understand. You’re probably familiar with refrigerator magnets and their north and south poles: they are “magnetic dipoles”. You can think of magnetic field lines as threading through the magnetic dipole and curving around from north to south. Magnetic fields are associated with magnetic forces: like poles of a magnetic dipole repel and unlike poles attract. Dipoles will try to line themselves up with the field: for instance a compass needle (which is itself a small magnetic dipole) will point in the direction of magnetic field lines. Lines which are closely bunched together indicate a strong magnetic field (associated with strong magnetic forces), and lines which are more sparsely spread out indicate a weak magnetic field (associated with weak magnetic forces).
