High School Thought Experiment on Charge Carriers and Electrical Conduction

[Pawan Kumar]

Thought Experiment on Charge Carriers and Electrical Conduction

Consider a hypothetical system involving a “miracle pipe” that contains no atoms, no nuclei, and no conventional matter. Inside this pipe exist two types of particles:

1. Electrons — identical to real electrons in mass, mobility, and behavior, carrying negative charge.


2. A hypothetical particle called “electrop” — identical to an electron in every physical aspect (mass, size, response to electric and magnetic fields, mobility, quantum behavior, etc.) except that it carries a positive electric charge of the same magnitude as the electron.

Assume:

• The pipe is electrically neutral overall (equal number of electrons and electrops).
• There is no lattice of positive ions, no protons, and no atomic structure.
• Both particles are free to move along the length of the pipe.
• An external electric field is applied along the pipe.

Questions:

1. Can a stable electric current exist in such a system?
2. If current flows, how should it be physically interpreted — as two opposite charge flows or as a single net current?
3. Would this system behave more like a metal, a plasma, or an electrolyte in terms of electrical conduction?
4. What would determine the resistance of such a system in the absence of a lattice (e.g., particle–particle interactions, collisions, collective effects)?
5. Are there known physical analogues to this system (e.g., electron–hole conduction in semiconductors or plasma conduction)?
6. Would magnetic fields generated by the current behave differently compared to conventional conductors?

I am particularly interested in whether charge neutrality combined with mobile opposite charge carriers alone is sufficient for electrical conduction, or whether a fixed positive background (such as atomic nuclei in metals) is fundamentally required.

 

[Nugatory]

Your hypothetical “electrop”differs from the positron (the electron’s anti-particle, and not hypothetical) only in that it doesn’t interact with electrons? They would form bound pairs with electrons (like positronium, but stable), these pairs would be neutral, and now we don’t have charge carriers or current.

I am particularly interested in whether charge neutrality combined with mobile opposite charge carriers alone is sufficient for electrical conduction, or whether a fixed positive background (such as atomic nuclei in metals) is fundamentally required.

Consider an old fashioned vacuum tube or CRT display. Current flows without any fixed background.

 

[Dale]

What you describe is just an odd plasma. It is odd because it is completely ionized and because the two charge carriers are approximately equal mass. But it is a plasma and would behave like a plasma and can be understood in that fashion.

1. Can a stable electric current exist in such a system?

Yes. Plasmas can and do conduct current.

2. If current flows, how should it be physically interpreted — as two opposite charge flows or as a single net current?

Either way is equally valid. Maxwell’s equations are linear.

3. Would this system behave more like a metal, a plasma, or an electrolyte in terms of electrical conduction?

It is a plasma so it would behave most like a plasma.

4. What would determine the resistance of such a system in the absence of a lattice (e.g., particle–particle interactions, collisions, collective effects)?

The resistivity of a plasma is commonly approximated by the Spitzer resistivity. This is based on collisions between the ions.

https://en.wikipedia.org/wiki/Spitzer_resistivity

5. Are there known physical analogues to this system (e.g., electron–hole conduction in semiconductors or plasma conduction)?

It is a plasma.

6. Would magnetic fields generated by the current behave differently compared to conventional conductors?

No. The only difference is that the plasma itself responds strongly to its magnetic fields. Everything becomes highly coupled.

 

[tech99]

An example of a device where positive and negative charges flow in opposite directions is the demountable discharge tube made by Teltron, https://www.healthandcare.co.uk/student-tubes/teltron-discharge-tube-s.html. This has a screen at each end, one showing the negative beam and the other the positive. The tube contains a plasma. The initial conduction occurs because electrons are pulled out of the gas atoms, but as the voltage is raised, collisions become more frequent, releasing more charge carriers, and a rapid increase in conduction occurs.