Magnetostatics: Feynman's Physics Explained
Magnetostatics studies the magnetic fields of steady currents. Two laws rule it: magnetic field lines never start or stop but form closed loops, and the circulation of the magnetic field around a loop is set by the total current passing through it (Ampere's law). And underneath it all, magnetism is a relativistic effect of electricity — a magnetic field is what an electric field looks like to a moving observer.
The big idea
Magnetic field lines always form closed loops, driven by currents.
Think about it
You can find the north and south end of a magnet, but never a lone magnetic 'charge.' Why, if field lines must close on themselves?
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