Explaining Negative Particles & Magnetic Fields

[Sammywu]

Hi, Beaty,

I bumped to this thread for researching some issues. I found your arguments and discussions very helpful to me.

I did have a misconception of current is the flow of electrons and I believe I am not alone. Your discussions clarified some questions I had. So if it did not befenited others, it benefited me.

I had one question. A current in a circuit is the electric charge flowing thriuth the medium and that caused a magnetic field arount the circuit.

But the electric charges in the circuit are summed as zero because the positive charges in the circuit shall cancel exactly the electric charges in the circuit even though it's flowing. So the current in the circuit shall not generate a electric field arund the wire. Is this right or wrong?

While a beam of electrons will not only generate a magnetic field around it and also an electric field.

How is your opinions on these statements?

Thanks

 

[krab]

Originally posted by Sammywu
So the current in the circuit shall not generate a electric field arund the wire. Is this right or wrong?

While a beam of electrons will not only generate a magnetic field around it and also an electric field.

This is true and has important implications for particle beams. A charged particle beam by itself generates both electric and magnetic fields and these counteract each other. The magnetic force self-focuses the beam; its force on the beam particles is -\beta^2 times as large as the electric force. At the speed of light, \beta=v/c=1, so the two forces cancel. At very low speeds compared with c, you have only an electric field. (BTW, You don't need to know anything about magnetic fields to derive this result, since it can be derived from a relativity argument.)

However, if you allow the electric charge of the beam to be neutralized by stationary particles of opposite charge (something that happens all on its own because the beam both creates low energy charged particles by ionizing the background gas, and provides the potential well for them to live in), you can end up with only a magnetic force. This force can be so large as to destabilize the beam (pinch effect).

 

[ZapperZ]

In condensed matter physics, the ground state of metals at T=0K corresponds to what is known as the "vacuum state" in quantum field theory. In this configuration, the states below the Fermi energy is completely occupied, while the state above the Fermi energy are completely empty.

Now, at finite temperatures, or due to fluctuations, you can have what is known as single-particle excitation above the Fermi energy. When this occure, you have an electron in a state above the Fermi energy, and a hole left behind in the filled states below the Fermi energy. But here's the deal - you can describe this new system EITHER by describing the electron that is above the Fermi energy, OR the hole in the filled states below that.[Refer to Mattuck's "Guide to Feynman Diagram in Many-Body Physics"] In other words, you can set your "universe" to be the empty states and consider the presence of electrons as your elementary excitation, or you can shift your universe to be filled with electrons and consider your elementary excitation to be these positive holes. It is similar in some sort to shifting your "gauge", or potential.

In this respect, the holes behave no different than a positive particle in vacuum (i.e if you shift your "vacuum" to be the level of negative electrons). We give it all the attributes of a particle - it has mass (or effective mass more accurately), charge, spin, etc... In fact, in condensed matter, the holes are the "antimatter" equivalent of the excited electron - i.e. they can anhilate to produce energy.

Now is this nothing more than a mathematical artifact? It isn't. The concepts of holes as a valid entity comes into play in many instances beyond just semiconductors. In high-Tc superconductors, the majority of the families of the cuprates are hole-doped! One actually remove electrons in the filled Mott insulator of the copper-oxide plane. The resulting holes behave like any other positively charged particle. In fact, this is the most common descrption of these family of compounds. Contrast that with the electron-doped cuprates that has generally lower Tc than their hole-doped counterpart, and you can already tell that there are some real physics differences involved here.

Keep in mind that these concepts, and the questions that have been asked in this string, can make more sense if one study a little bit of many-body physics. Only then would one see why things like "holes" and "excitations", etc, are more transparent. It is only within the many-body context would these things have definite meanings.

Zz.

 

[wbeaty]

Originally posted by Integral
What are you arguing about? I have asked you to moderate your tone twice, here is a third time. Calm down. Are you capable of discussing these matters without the inflammatory attitude?

You want to talk? Not without other moderators watching.

I honestly have no idea what you're talking about. What "tone" am I supposed to change? *What* inflammatory attitude? As far as I know, I'm behaving exactly the same as I always do on numerous forums (several of which I moderate.) You'll have to be far more specific if you want me to understand your complaints.

I certainly am pointing out your physics errors in no uncertain terms. Is this what you're really objecting to? If not, then please quote me the specific sentences in my messages which give you problems. Also please tell me which forum rules they violate.

You're obviously not an internet newbie. You should be well aware that "tone" of messages is frequently all in the mind of the reader, not in the message itself, and therefore is not a reliable indicator. If you're sure that I'm misbehaving in some way, you need to make certain that the "tone" is not all in your own head. It's easy: quote me the specific passages where I break the rules of physicsforums.com

I suggest you take a look at this article:

Email lists: flamewars and psychology
http://amasci.com/lists.html#fl

Also this one about electric current that I posted earlier:

Which way does "electricity" flow in circuits?
http://amasci.com/amateur/elecdir.html

If you have a few hours, take a look at my collected writings:

Electrical articles
http://amasci.com/ele-edu.html

Or the rest of my site:

amasci.com: the good stuff
http://amasci.com/unew.html

William J. Beaty
Research Engineer
University of Washington
http://staff.washington.edu/wbeaty/
http://amasci.com/

 

[chroot]

There's really no need to continue this thread. wbeaty, please let this argument go. It's not worth the effort to re-open it.

- Warren