Magnetism seems distinct from electricity but Maxwell’s equations describe both, and experiments connect them. A static charge isn’t magnetic but if it moves, a magnetic field appears around it. In Figure 5.12, passing a current I through the wire produces a magnetic field B. Wrapping a wire around a nail and passing a current through it makes it a magnet, and that effect stops when the current does. Electricity can then cause magnetism and the reverse is also true, as spinning a magnet with a wire around it induces a current in the wire. Electric cars are possible because magnetism and electricity connect:
“We will see that magnetism and electricity are not independent things – that they should always be taken as one complete electromagnetic field.” (Feynman et al., 1977).
Is magnetism then just charge in another guise? (Note 1) It would seem not because:
1. Static charges and magnets don’t interact.
2. The magnetic field is at right angles to the electric field.
3. Gauss’s law doesn’t apply to magnetism, which reduces more like an inverse cube.
4. Dividing a charged body gives positive and negative charges but dividing a magnet gives two more magnets, both with a north and south pole.
Magnetism acts differently from charge, so how they relate is unclear. For example, light is described as orthogonal electrical and magnetic waves that cause each other in a self-sustaining loop, which is illogical. Current physics can explain electricity and magnetism separately, but not how they combine. It is as if we understood horses and birds then found a winged horse that shouldn’t be possible. No credible theory explains why electro-magnetism has two different effects, that occur in different directions, and weaken differently.
The standard model answer is that charges repel when virtual photons push them apart, but the same photons also make charges attract, and move magnets, so fairies with photon wands would explain electro-magnetism just as well. One field with different effects needs different causes, not the same cause that conveniently produces what is observed after the fact.
Note 1. The logic is that a moving electron’s length is foreshortened by special relativity giving more negative electrons than positive protons in a given length of wire, so parallel wires with opposite currents attract, but this could be correlation not causation