# No Such Thing As Magnetic Flux Density

1. Jul 28, 2009

### rockyshephear

I would like to put this out for argument that there is no such thing as magnetic flux density. Since magnetism is a wave like on water's surface, it is continuous. Is there a 'water wave density?" I think not. Unless you mean the distance between wave peaks. But flux lines are only arbitrary man made conventions with no basis in reality so you can't say the this flux line is closer to the previous than the subsequent one. Flux lines are continuous. So where does the 'density' come in to play?

2. Jul 28, 2009

### LeonhardEuler

You are right to think of it as erroneous to interpret magnetic flux density as a number of magnetic flux "arrows" per unit area, but that is not what it is supposed to be.

I think what is confusing you is the fact that you were probably taught to draw magnetic fields in such a way that the density of lines indicates the strength of the field. You are right that the number of lines you choose to draw is arbitrary, but the magnetic flux density has nothing to do with how many lines you choose to draw.

Magnetic flux itself represents the extent to which a magnetic field penetrates through a surface. It is calculated by $$\int\int\vec{B}\cdot dS$$. Magnetic flux density is just the magnetic flux through a surface, divided by the area of the surface. It makes no reference to the number of lines in a diagram.

3. Jul 28, 2009

### rockyshephear

But imagine that flux density equates to soldiers crossing a border. You are saying it's not the number of soldiers because it's not the density of the flux lines. What constitutes intensity of penetration? It has to be a quantititive thing, a count of something that makes more or less penetration. Yes? No? lol

4. Jul 28, 2009

### Staff: Mentor

There are unfortunately confusing variations in magnetic terminology between some textbooks. However, in most introductory physics textbooks in use in the USA, I think "magnetic field" and "magnetic flux density" are simply two names for $\vec B$.

5. Jul 28, 2009

### rockyshephear

Still what fundamentally is penetrating a surface to give more intense magnetism vs less intense magnetism if the density of the flux lines is not the cause? Is it the magnitude of the infinite vectors that quantifies the intensity of the magnetism penetrating a surface?
And if so, what does the magnitude of a vector mean? Just a strong kind of push or pull at that exact point?

6. Jul 28, 2009

### Phrak

Are you aware that Faraday's lines of flux are not distinct lines running through space containing magnetic influence with where the space inbetween would have no influence? The lines you see in drawings of magnetism are schematical, not physical.

With your curiousity about all this--in several threads, you would be better satisfied with a class, or a book. The little tid-bits you obtain here are far less than understand this subject formally.

7. Jul 28, 2009

### rockyshephear

Yes I'm aware. What I'm really fascinated with on the is forum is how infinitely intelligent all you guys are but you can't seem to describe fundamentally whats going on in any terms but math, which by my definition is not the best way to learn about the physical world. To me, you formualte analogies then you combine the math and it makes sense. If you took a caveman and told him F=MA, he'd would never, ever, ever get it. But if you told him...
BIGGER APPLE, HIT YOU ON HEAD, HURT MORE
he'd get it better.

8. Jul 29, 2009

Staff Emeritus
The magnetic field is H, and the magnetic flux density is B. In vacuum, they are identical. In materials, they differ by permeability (multiplicatively) or magnetization (additively). Some problems are simplest if you use B, some if you use H.

Denying that magnetic flux density exists because one doesn't understand it is, I am afraid, crackpottery. I don't have a better word for it - how else would you describe the conclusion that "everyone else has it wrong - even people who have studied it longer and harder than I have"?

9. Jul 29, 2009

Staff Emeritus
I've suggested a book multiple times. To no avail, I'm afraid.

10. Jul 29, 2009

### rockyshephear

I have read multiple books on the topic and watched hours of MIT lectures and other lectures so interacting here is to help with all that. If you guys are getting too frustrated to take the time to respond, just pass up on replying.

11. Jul 29, 2009

Staff Emeritus
And yet you still don't understand. There's a difference between reading something and understanding it. (To quote an old movie, "Aristotle was not Belgian. The central message of Buddhism is not 'every man for himself'. And the London Underground is not a political movement!")

But you're posting nonsense! When you say that because you don't understand it, there isn't a B field, do you expect the people who know better to keep silent?

12. Jul 29, 2009

### maverick_starstrider

I'm intriuged. What movie is that?

13. Jul 29, 2009

### Born2bwire

14. Jul 29, 2009

### A.T.

But it is the way physics describes the physical world. If you don't like it try philosophy or religion.