Electromagnetism

Electromagnetism is one of the fundamental physical forces in the universe.  It is basis for the explanation of a number of phenomena in particular:

  • The various aspects of electricity and magnetism
  • Visible light radio waves and other forms of radiant energy
  • Friction and surfaces


It can be explained in the following way:

The force experienced by two charged particles  near each other + and - or  + and  + or - and - experience a force called a electric field and is the caused by the exchange of virtual photons at the speed of light.


The black dot represents  charge-  and red dot represents charge+. image: MIT.edu


If one of those charged particles moves towards or away from each other or move around each other not much happens. The particles just experience a greater or lesser force. 

But if at some point one of those charges suddenly turns into the opposite charge. The charges then repels. 

If those charges are also moving, the field lines you see will join up with each other (not join up with a an other point charge) to form a 'bubble'. The bubble,  because it is made up of a field that is moving at the speed of light, moves away at the speed of light.

What happened to the magnetic field? Well it turns out that the only way to get those charges to move is by using a magnetic field. 

The magnetic field that was present moving those particles also gets combined into the electric field, but at right angles. Hence it gets called an electromagnetic wave.

It goes further that electromagnetic fields can be viewed as a particles called photons.


Commentary:

Ok most physics courses (or physicist) say there is a significant difference between an electric field and an magnetic field. They are in fact even measured differently. (Though I suspect you can convert values from one to another)

Typically they say that a moving point charge, oscillating, produces an electromagnetic wave with an electric field at right angles to the magnetic field.

like this:

EB_Light_320.jpg

image of classic electromagnetic wave. image MIT.edu

But is this really what happens in nature? not really quite that simple.

Light gets to our eyes for example as a 'blob' of electromagnetic energy, sometimes called a photon or wave.

Maxwells equations describe how an electromagnetic wave is produced and propagates .

It turns out  electromagnetic waves propogate more like this:

MicrowaveAntenna_320.jpg

Those connected 'loops'  or 'blobs' are electromagnetic waves. In this case 'radio waves' as they are quite large. For visible light those 'loops' are very small. image: MIT.edu


Wikipedia puts it nicely as:

According to the special theory of relativity, the partition of the electromagnetic force into separate electric and magnetic components is not fundamental, but varies with the observational frame of reference:

 An electric force perceived by one observer may be perceived by another (in a different frame of reference) as a magnetic force, or a mixture of electric and magnetic forces.

source:wikipedia