# Electromagnetic wave /Field question

1. Mar 16, 2012

### zak8000

Hi

i was wondering whats is the difference between electromagnetic waves and fields or is a field just a number of electromagnetic waves. also i was wondering is it possbile to have an electromagnetic wave where there is only a magnetic field and no electric field and vice versa

Thanks

2. Mar 16, 2012

### Bob S

Good questions.

First, you can have a steady dc electric field or a magnetic field, without the other. This is true even if the dc field varies in space.

If either the magnetic field or the electric field is varying with time, then you have to have the other field also, because the two varying fields are coupled by Maxwell's equations.

Bob S

3. Mar 16, 2012

### yungman

This is a good question, both electric and magnetic field are vector fields which is a point form. By point form, it means the amplitude and the direction is defined at every point in space.

By definition of EM wave, it is a varying field where Bob S answered already that in a varying field, E and M and coupled together by Maxwell's equations.

BUT on top of all the above, there is a propagation of the EM wave that I am not absolute sure. I believe it is still a vector field at every point in space, it just vary in the direction that "looks" like as if it is moving.

Remember the explanation of water wave with a floating balls? The over all wave looks like it is moving in a certain direction, but if you throw a bunch of floating balls into the water wave, they only bobble up and down vertically!!!! With this, I would say the EM wave is a vector field that "bobble" is a stationary point.

Someone with more authority might want to jump in to confirm this. I am still learning.

Last edited: Mar 16, 2012