# Speed of flux

1. Feb 7, 2006

### pinestone

At what speed does a magnet's flux field travel

2. Feb 8, 2006

### Tide

If it's travelling then it is electromagnetic meaning that it travels at c.

3. Feb 8, 2006

### pinestone

How can it be "electro" ? It's just magnetic. Isn't magnetism a force, and not a wave? A wave occurs within a period of time. There is no reference frame for flux. A magnetic field is a continous loop- A bi-directional and inter-dependent pair of forces.

"Question everything"...Albert Einstein

Last edited: Feb 8, 2006
4. Feb 8, 2006

### ZapperZ

Staff Emeritus
Check the Maxwell equation. I can easily describe a magnetic field as a varying E-field. Furthermore, the speed of propagation of a magnetic field is no different than the speed of propagation of E field. Both of these are tied together at birth!

Zz.

5. Feb 8, 2006

### pinestone

It has been suggested that magnetic lines of force (flux) travel (if, indeed they do) at the speed of light. This seems to be the current theory, anyway. And, what capacitor could slow light down to 88 mph?

6. Feb 8, 2006

### Cyrus

So, if I am to understand this correctly, a person asked in a previous post about time delay in the measurement of an E field of a star moving away from an observer. In that case, an E field would be distinct at every instant in time. So lets say at time $$t_0 + \Delta t$$, the charged star has moved an incremental displacement away, $$v \Delta t$$. So the new E field being created at this instant would be based on the new $$\frac{1}{r^2}$$ relationship, $$\frac{1}{(r+v \Delta t)^2}$$. Assuming the E field is steady and constant at time $$t_0$$, it would take $$\frac{r +v \Delta t}{c}$$ seconds before the new value of the E field from time $$t_0 + \Delta t$$ reaches the observer. So I would see the E field associated at time $$t_0 + \Delta t$$, at a later time, $$t_0 + \Delta t + \frac{r + \Delta t}{c}$$? Is that correct? Probably not..

Last edited: Feb 8, 2006
7. Feb 8, 2006

### pinestone

Yes, and Maxwell's equation provides us with zero. So these "electro" magnetic lines of flux are somehow being propagated by electron motion from what source of EMF ?

8. Feb 8, 2006

### ZapperZ

Staff Emeritus
Er... come again? Maxwell equations provides us with zero? I don't understand what you mean here. And it is being propagated by electron motion? Can you please show me where you get this? Maybe I can understand it better looking at the equation being described here.

Look, when you have a magnetostatic condition, there is no "speed" of propagation. Nothing is changing, so you have no way of measuring the speed of anything of the field. The word "flux" should not be confused with the pedestrian usage of the word. A "flux" in this context is simply

$$\int{B.dA}$$

Zz.

9. Feb 9, 2006

### dextercioby

In this context FLUX$\neq$ FLOW...

Daniel.

10. Feb 9, 2006

### AlphaNumeric

If you missed the joke, he/she was referring to the films 'Back to the Future' where the time machine has a flux capacitor and the car has to reach 88mph before it would be able to travel in time.

11. Feb 9, 2006

### pinestone

Yea, I got the joke. What is so funny about the word "flux"? This is a classical physics forum, isn't it? A flux capacitor belongs in QED, and not here. And just for reference, there really is a flux capacitor- try Google.

12. Feb 9, 2006

### pinestone

You say that the "electro" magnetic lines of force (aka "flux") have no measurable motion. No speed. No movement. And, they are at rest. If so, which kind of "electron" has no motion?

13. Feb 9, 2006

### ZapperZ

Staff Emeritus
Is there a reason why you keep invoking electron motion? Why would "electron" be a part of this? Please show me a formulation of magnetic flux that explicitly involves "electron motion".

You are asking me to explain something that only you have seen or understood. I'm sure you realize what an impossible task this is. If you could cite a clear reference where you understood or read these things, it will be me a lot easier, since obviously, we are getting nowhere fast on this.

Start by defining a magnetic flux.

Zz.

14. Feb 9, 2006

### pinestone

Yes, OK- I'll reply to you soon...:shy:

15. Feb 9, 2006

### skywolf

you dont detect a wave untill the entire wave has passed your sensor right? in that case, wouldn't you detect the speed of flux to be slightly lower than c?

16. Feb 9, 2006

### ZapperZ

Staff Emeritus
So you see the sun during night time then?

Zz.

17. Feb 9, 2006

### Tide

Not exactly. By your argument you would also have to take into account the same lag required for the "entire" wave to have been emitted.

18. Feb 9, 2006

### pinestone

As I understand it, a magnetic field is an entity produced by moving electric charges which exerts force on other moving charges. These electric charges are a characteristic of subatomic particles. One of these particles being an electron. Did I miss something here?

19. Feb 9, 2006

### ZapperZ

Staff Emeritus
Yeah, but the moving charges that produces the magnetic field does NOT travel with the field! It is the source, but you were asking about the magnetic flux. I asked you to look at the definition of a magnetic flux. You will see that the source doesn't "flow" into the area that is being measured for the flux.

Besides, moving charges is CURRENT, not a magnetic flux.

So tell me what exactly do you want?

Zz.

20. Feb 9, 2006

### pinestone

For a measured quantity of magnetism, is it moving? And if it is, at what speed?