# The Two forms of Maxwell's equations

1. Nov 26, 2008

### DeepSeeded

Hello,

I was tempted to put this in the math section but it is more of a visualization problem though it is most likley due to my lack of understanding the divergence and curl operators fully.

I am comfortable with the closed loop integral of E dot dA and can visualize it as a solid closed surface. However when I think of the divergence of the E vector I think of a tiny little peice of the E vector.

How can these be the same thing?

Same goes for the Curl vector being the same as the closed loop integral of a line.

In 8.02 they used the integral form, in 8.03 they are using the differential form and now I am confused.

2. Nov 26, 2008

### nasu

The integral of the E dot dA is not a surface but the flux through that surface. You can visualize it as the "amount of field" crossing the surface. This is not the same as the divergence but same as the integral of the divergence over the volume included in the surface.
The divergence is the flux through a tiny, infinitesimal, closed surface (divided by the volume inside the surface). By integration of the divergence over the volume you just add all these fluxes inside the volume included by the surface and end up with the "total" (net) flux through the surface.

You can write Maxwell equations in differential or integral form. It does not follow that the flux is equal to the divergence.

3. Nov 26, 2008

### DeepSeeded

OK, my misunderstanding was that the definition of the divergence is an infinitsmal sphere which is closed and not an open point. I see that it says this now on wikipedia but it was not so clear.

Looks like the definition of the curl is an infinitsmal closed line integral which also works to explain Ampere's laws.

I think I am getting it now, thank you.

4. Nov 27, 2008

### Naty1

Those ideas are subtle and require some attention and patience when your firstencounter them. Try looking for other interpretations and explanations and reread the ones you like several times over a few days...took awhile to for those ideas to sink in for me...

I'm always amazed at the people who first dreamed these kinds of things up...pretty classy!!!