Field Electron Emission: How Much Charge Can You Remove From a Sphere?

[Smacal1072]

If you have a sphere of metal electrically isolated by a vacuum, and continuously add negative charge to it, the metal will eventually discharge due to field electron emission. This depends primarily on the work function.

Take the same situation as above, but continuously remove negative charge from the sphere. I know that the positive charge will accumulate on the outside of the metal sphere - how much negative charge can you remove before the skin of the sphere starts shedding?

 

[Born2bwire]

Probably a lot more, the positive charge are the ions of the metal atoms that are being held in the lattice. The electrons are the charges that are mobile and easily stripped off. To expell the ions you would probably have to compare the resulting ionic (Coulomb) forces with the Van der Waals/London forces that hold the metal lattice together.

 

[charng]

I can provide some insight into this question based on the principles of field electron emission and the properties of metals. In the first scenario, where negative charge is continuously added to the isolated metal sphere, the discharge process is known as field electron emission. This occurs when the electric field at the surface of the metal exceeds a certain threshold, causing electrons to be emitted from the surface. The amount of charge that can be removed from the sphere in this scenario depends on the work function of the metal, which is the minimum energy required to remove an electron from its surface. The higher the work function, the more difficult it is for electrons to be emitted and the more charge can be accumulated on the sphere before discharge occurs.

In the second scenario, where negative charge is continuously removed from the sphere, the positive charge will accumulate on the outside of the metal sphere. This is known as the skin effect, where the electric field is strongest at the surface of the conductor. The amount of negative charge that can be removed before the skin of the sphere starts shedding depends on the strength of the electric field and the properties of the metal, such as its conductivity and surface area. Once the electric field at the surface of the metal exceeds a certain threshold, the electrons will be emitted and the skin of the sphere will start to shed.

In both scenarios, the amount of charge that can be removed from the sphere is limited by the properties of the metal and the strength of the electric field. The exact amount will vary depending on the specific conditions of the experiment. However, it is important to note that continuously adding or removing charge from a metal sphere can have detrimental effects on its structural integrity and may lead to damage or failure. Therefore, it is important to carefully monitor and control the amount of charge being added or removed to avoid any potential hazards.