Page 1 of 3

The Nature of Charge

Posted: Sat Feb 18, 2006 3:37 am
by Hayabusa

Re: The Nature of Charge

Posted: Sat Feb 18, 2006 3:55 am
by Hayabusa
I’m trying to tie in relativity into this.

A charge creates two fields.

The first field is an electrostatic field, which is static in magnitude, and extends radialy outward from the charge.

The second field is the magnetic field. It has a variable magnitude which is proportional to the Inertial frame of the observer relative to the inertial frame of the charge.
Its field also has the direction of circling the axis of this relative direction.

Here’s what’s weird about this theory. For the magnetic field, its magnitude, and direction depends entirely on who the observer is, and can only be established if there is an observer. Where the observer is in a different inertial frame as to the charge (i.e. the charge is moving relative to the observer).

Is this correct???
Any thoughts

Re: The Nature of Charge

Posted: Sat Feb 18, 2006 9:46 am
by DaveC
Is the general idea correct? I would say "Yes", more or less.

A stationary charge does no work. The detection of its "field" -the force between the charge and a small test charge - is assumed to be an arbitrarily small energy process, so as not to perturb the field of stationary charge. Reasonable enough.

If the charge is in motion relative to the observer, its motion constitutes a current which will have an associated magnetic field circling the charge's path in one direction or the other, depending on direction and charge polarity.

This perceivable (detectable Magnetic field) does no work either, until and unless it interacts with something conductive or magnetic. When an interaction happens, then energy is exchanged and the moving charge changes velocity and possibly direction. Conservation of energy seems to work, as does conservation of momentum.

So the establishment of a magnetic field which does nothing but depends on the presence of an observer, while seemingly a bit odd, is actually quite reasonable, and consistent.

Dave Cooper

Re: The Nature of Charge

Posted: Sat Feb 18, 2006 10:35 am
by Todd Massure
This has been something I've pondered before.
Take an electron beam traveling at let's say approximately the speed of the beam in a CRT display ~ 30kev. The beam stays columnated because of the magnetic field it produces due to it's motion (pinch effect), BUT, what if the observer is traveling along side at the same speed - would there still be a magnetic field to keep the beam columnated? What if there are two observers, one stationary and one moving along side? Hmmm...


Re: The Nature of Charge

Posted: Sun Feb 19, 2006 5:56 am
by Donald McKinley

I'm sure I'll get clubbed about the ears for this, but here goes. This is based on the presumption of the electromagnetic force being the only fundamental force.

If you hope to ever understand this topic on a low level you have to think in low-level terms. When you speak of measuring magnetic fields, you are already on a higher level that deals with matter and charge and reactive forces.

If you will forgive just a teenie weenie little bit of handwaving, IMHO The lowest level manifestation of the electromagnetic force consists of three components which sustain each other and cannot exist without each other. Those three are the electric effect, the magnetic effect and the accelerative effect. Even the name electromagnetic force suffers from an embarrassing lack of respect for the accelerative force.

There are those here who think that magnetic effects are a relativistic phenomena. That is the understanding presented in Richard Feynmans 3 Volume lectures on physics. (Forgive my narrow reading) If you are talking about a high level in the realm of charges and matter, that may be true in a sense, but I believe that the components of the EM force are the cause of relativity and not the effect. Need to be very careful in the attribution of causality.

On a low level, measurements cannot be made. Reality must be inferred. Making some simplifications (which is a dangerous thing), Electromagnetic effects are propagated spherically unless there are impediments. If this is true this means that the magnetic force is also propagated spherically. If it isn't then you are saying that electrical effects can exist without magnetic effects. This cannot possibly be true.

When you think on a low level, its imperative to always keep in mind the right hand rule and all three components. Try not to use compound applications of the right hand rule. Keep in mind that in the case of an object that is moving there will be an equal magnetic field and electric field associated with the motion. If the object is charged, then you have compound fields that rapidly become confusing because each portion has its own 1 to 1 to 1 relationships and if one component of the three happen to coincide and not cancel it is easy to start ignoring things.

I strongly doubt whether on a low level, (before particles) there are any internal reactive forces at all because of the 1 to 1 to 1 relationship of the components of the electromagnetic force. I seems that the 1/1/1 internal relationship must be instantaneous. This is definitely in contrast to reactive EM forces where there are hysteresis delays and the acceleration is not intrinsic but is supplied from outside. I believe that the quantisization of physics results from the non changeable nature of the 1/1/1 relationship.

I have never met anyone who had a good understanding of the low level EM force (I should call it EMA with the A standing for acceleration)

Anyone who understands the EM force well should be able to explain the origin of hysteresis as well as thermodynamics from an electromagnetic point of view. Also the origin of mass must be explained. I draw a blank even though I believe that it is probably true.

If you want to make progress you have to work through a lot of seemingly flaky ideas. Most of them will, of course, not pan out.


Re: The Nature of Charge

Posted: Mon Feb 20, 2006 4:51 pm
by Richard Hull
An electron beam in a CRT WILL NOT self-focus due to pinch forces! Whether you are at rest observing the beam or riding along with it, ALL the electrons will repell from one another at all times! The beam will be observed to fan out. This is regardless of whether you are part of the beam or watching it from the outside.

In a CRT, the beam is, initially, electrostatically focused, (electron gun). It is EXTERNALLY, magnetically held intact and guided by a coaxial mag field, (deflection yoke). The electrons are accelerated to hit hit the screen by the anode.

The electrons want to scatter to the four winds the instant it leaves the gun! Only the externally generated magnetic field of the yoke keeps those puppies from leaving the crowd. The energy expended in the average deflection yoke is significant!

Electrostatic forces never rest, they never letup, they never go away. They are primal! Only a heaping helping of outside energy, properly applied, will offset these natural urgings, keeping them together and on a collision course with the TV screen.

The pich effect is an effect of extreme current as there is no significant current in a CRT electron beam, the magnetic field presented by the electron stream in a CRT is close to ZERO, as is the pinch effect!

Richard Hull

Re: The Nature of Charge

Posted: Mon Feb 20, 2006 10:21 pm
by DaveC
Richard is correct here, of course.

The electron's charge exerts a mutually repulsive force on all other electrons in the beam. The beam focuses because there is an inward momentum (radial direction) imparted by either the electrostatic force from the focus lens or the external magnetic force on the moving charges. Most CRTs use electrostatic focus these days.

So electron beam focus is the result of an external force for LOW current e beams.

At very high current densities, the e-beam can become self focusing. Don't have that current density at my fingertips, but it's far beyond normal CRT current densities, - I'm thinking kilo amps per sq mm, - and quite probably beyond the emission capabilities of the standard tri-oxide cathode materials.

That's a fun calc.... I'll take a stab at it later today.

Dave Cooper

Re: The Nature of Charge

Posted: Tue Feb 21, 2006 5:03 am
by longstreet
I can't see how it's possible for a beam of electrons to ever be self focusing. At least with the special relativity trick of putting yourself in the viewpoint of the electrons, you can see there is no way for the charge density to reach zero, and definatly not become positive since there aren't any positive charge there to begine with.

Re: The Nature of Charge

Posted: Tue Feb 21, 2006 6:38 am
by DaveC
Carter - From the hitchhiker's viewpoint it DOES seem a bit mysterious. From the stationary observer's vantage point the moving charges produce a magnetic field, that can easily be detected, with either a compass, an inductive link (current transformer or Pearson coil) so something is there.

I think the field is perceived by the hitchhiker, whenever there is a tendency for the charge density to change.That dQ/dt makes a corresponding dE/dt which generates a local magnetic field B. Conservation of energy (Lenz's law in other garb) sets the B field to oppose the charge density change, thus tending to keep it constant. This is part of the self focusing effect.

The rest comes about when the charge is initially accelerated, which generates a focusing B field.

The part that is intriguing here is whether there can be a "field" that your meters (the hitchhiker's ) can't measure. Sort of like the tree falling in the forest, question.

Dave Cooper

Re: The Nature of Charge

Posted: Tue Feb 21, 2006 6:41 am
by Hayabusa
I'm guessing that the self focussing effect (if it in fact exists) is do to the magnetic field.

As the electrons move they produce a magnetic field, and with more then one electron these fields combine, and create a force in the direction of pulling the electrons in closer.

If my guess (above) is correct, then wouldn't this effect become more pronounced with increasing electron velocities (i.e. higher voltages)?