The study of magnetism involves the interaction of the Magnetic Fields formed in various materials, and the forces involved with them. There are some key differences between magnetism and charge
Dipoles & Monopoles
In electrostatics, an object can be positively or negatively charged, but not both. While a bigger object can contain many smaller positive and negative charge carriers, these charge carriers cannot contain both charges at once. In that sense, we can have dipole charges (a combination of a positive and negative charge), or monopole charges (just one of them).
The same does not apply for magnetism. Magnets are defined to have a north pole and south pole, analogous to the positive and negative charges. Magnets can only exist as dipoles in nature. While there is a hypothetical case for a monopole, it hasn’t been discovered…yet. The lack of monopoles create some very distinct differences between charges, poles and their respective forces and fields.
Why south and north?
Earlier, a lot of discovery in magnetism began with observing the effect of the Earth’s magnetic field on objects. As such, the two magnetic poles are named after the earth’s poles.
- Essentially, the magnetic force is formed when two charges are moving together.
- B-force violates newton’s third law, as vectors point different directions
- Magnetic force is reference frame-dependant -> we can always move to a frame where v1 or v2 is zero, making it have 0 magnetic field. However, to transform to this frame, we have a displacement in the electric field, which contributes to the momentum
- B-force = E-Force * v1v2/c n