I Build Setup to Create Electric Damping Force

[Malamala]

Hello! Is it possible to build a setup (containing time dependent and independent electric fields), such that a charged particle will feel a force proportional to its velocity i.e. $ma = -\alpha v$?

 

[Baluncore]

Magnetic deflection is proportional to velocity, but it is sideways.
Which direction do you want the force to operate ?
http://www2.hawaii.edu/~jmcfatri/labs/magdefl.html

 

[Malamala]

Magnetic deflection is proportional to velocity, but it is sideways.
Which direction do you want the force to operate ?
http://www2.hawaii.edu/~jmcfatri/labs/magdefl.html

Sorry, I meant a damping like force, so in the opposite direction to its motion.

 

[kuruman]

I don't think it can be done. You want a damping force like friction no matter what the direction of the velocity is. Electric fields are conservative. If the particle moves from A to B and then from B to A you need to reverse the field when the particle reverses direction which means you need to somehow sense the change of the particle's direction of motion as well as the speed. Sounds like a tall order to me because a passive electric field won't do the job.

 

[Twigg]

To second @kuruman, I don't think it's possible because a damping force is irreversible (it increases entropy). The Lorentz force is time-reversal invariant, so you're guaranteed you'll never get a damping force. The only way I could see this working is if you "somehow" scatter EM waves off the charged particle in a way that increases the entropy of the scattered wave while reducing the entropy of the charged particle, but conserves the entropy of the whole system (incident wave, scattered wave, and charged particle). For example, if you put a hot plasma in a colder blackbody oven, I imagine that the two will thermalize, cooling the plasma and heating the blackbody radiation.

 

[Twigg]

It occurred to me that LIGO's mirror cooling scheme may actually satisfy what the OP is looking for.

Is it possible to build a setup ... such that a charged particle will feel a force proportional to its velocity i.e. ma=−αv?

It's not possible using only the electric field, but it is possible if you have "something else" to measure the particle velocity in real time and you actively change the direction of the electric field to slow the particle down. This is, in a nutshell, what LIGO does to cool their kg-scale mirrors to an average quantum number of something like 10 IIRC. I guess you could call it a Maxwell's demon, but I'm scared now that I've said this because I use that term pretty loosely and I feel like a bunch of smarter folks are going to rip me a new one

 

[tech99]

Hello! Is it possible to build a setup (containing time dependent and independent electric fields), such that a charged particle will feel a force proportional to its velocity i.e. $ma = -\alpha v$?

Does this happen in a resistive material?

 

[vanhees71]

https://physicsworld.com/a/ligo-mirrors-have-been-cooled-to-near-their-quantum-ground-state/
https://arxiv.org/abs/2102.12665