Electricity and Magnetism

Notes for me: EM field is a classical (non-quantum) field. It is described as a "Quantized Electromagnetic Field Tensor" in QED, which is the quantum counter part of the classical field.

• The universe is comprised of basic fundamental fields as we have learned to describe it, and each field has it's own particles, which are points in space that affect the values of the field at that point.
• Each point in space has a specific value for the intensity of each field at that point.

• We have the electromagnetic field,

• The basic field is electromagnetic, but depending on our non-accelerating frame of reference, we will measure the values of electric field and magnetic field values differently.

• That is, there are no separate electric and magnetic fields, because both are connected aspects of the electromagnetic field.
• One could say that the magnetic field is just a relativistic effect of the electric field in certain non-accelerating reference frames, but the one would have to always stick to a non-accelerating reference frame where the charge carriers in question are stationary.

• And they would certainly not be able explain the fields from a charge an a magnet kept together in a system, or at least a stationary charge and a moving charge.

• Changing electric field at a point produces a changing magnetic field at that point and vice versa.

• We call this electromagnetic induction, that is, the induction of a change in magnetic field from a change in the electric field and vice versa.
• To do that, we have to accelerate a charge carrier, which are the only things through which we can alter the field.
• We can also move magnets, which are aggregates of moving electrons producing a magnetic field.
• That is, we can only move charge carriers or aggregates of charge carriers, and we only have charge carriers for the electric field, but not for the magnetic field since we haven't observed any magnetic monopoles.

• Again, this change is due to the fact that to bring about this change,

• Changing acceleration of a charge carrier produces a change in the change of an electric field, that is a change in the magnetic field, and that will produce yet another electric field outward, and as the magnetic field keeps varying, that electric field will also keep varying and hence the disturbances keep propagating outward as a wave.

• The key idea here is that electrons in a circuit move at a drift velocity rather than accelerate, and that is why there is no change in the magnetic field.
• The reason there is no change is because when it is moving at a constant velocity, since the speed of light is constant too, there is always a non-accelerating frame of reference in which the charge carrier is stationary, but the electric field is not
• Now, an initial change in the electric field from the default value as an electron flows, accelerating until it settles at a drift velocity will produce a corresponding change in the magnetic field, and surely it will generate and electric field and so on.
• But that is weak as compared to an actively oscillating strong electric field or magnetic field, as we achieve with generators or batteries.