Wikipedia:Reference desk/Archives/Science/2019 December 26

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December 26

Movement of a mobile electric charge around a static electric charge

What kind of work and what type of force provides the energy necessary to the motion of a mobile electric charge q around a non-mobile electric charge Q giving the potential energy associated to the electric potential

$V_{\mathbf {E} }={\frac {1}{4\pi \varepsilon _{0}}}{\frac {Q}{r}},\,$

at distance r from it?--109.166.134.81 (talk) 16:24, 26 December 2019 (UTC)

The work is the change in potential times the charge on the mobile bit due to the move. ie qΔV_e. The force between the two will be the charge of the mobile times the gradient of the electric potential of the fixed item. q∇V_e Note this will give a vector, and the force will be in the direction of the product of the charge, so two positive charges will give you an outward force. Graeme Bartlett (talk) 20:03, 26 December 2019 (UTC)

An interesting case appears when the position vectors in two points A and B r_A and r_B are equal as two radiuses of a same cercle, the two points are equi(iso(?))potential, so the work will be zero. This situation is quite surprising, motion with zero work.--109.166.134.81 (talk) 21:57, 26 December 2019 (UTC)

An example of zero work motion of Coulomb force occurrs in Bohr model of the atom where the Coulomb force is in static equilibrium with the centripetal force.--109.166.134.81 (talk) 21:59, 26 December 2019 (UTC)

Or in order to have a non-zero work, perhaps arclength and tangential force are involved in the scalar product force - distance of work?--109.166.134.81 (talk) 00:05, 27 December 2019 (UTC)

If you are wanting to know what can do the work on a charge, in an atom, that could be a photon. Or it could come from bumping into another atom, and this would come about because of another electric charge on another particle affect your mobile charge of interest. Graeme Bartlett (talk) 00:38, 27 December 2019 (UTC)

Are disintegrator Weapons possible, at least in theory?

I’ve grown up with sci-fi movies like “Forbidden Planet”, television shows like “Star Trek” and video games like the “Fallout” series. This has made me curious whether or not it would be theoretically possible that a weapon could exist, which could disintegrate objects. Also, wouldn’t such a weapon be (theoretically speaking) dangerous for the weapon user as well, because of the very high temperatures?--2A02:120B:C3E7:E650:A931:29B9:FE86:2516 (talk) 19:52, 26 December 2019 (UTC)

Our article on this is titled raygun. Onother is the Plasma weapon. There are also real directed-energy weapons (Pulsed energy projectile, Particle-beam weapon, Laser weapon, Sonic weaponry). Graeme Bartlett (talk) 20:28, 26 December 2019 (UTC)

They're called nuclear weapons. At the center of the fireball, temperatures can exceed 10,000,000 Kelvin, which is above the boiling point of pretty much everything. As you indicate, you don't want to be next to one when it goes off. --47.146.63.87 (talk) 08:28, 27 December 2019 (UTC)

A true disintegrator would cause something to fall apart at an atomic level. It would break the atomic bonds, causing all the molecules to simply fall apart. That is a very different process than burning something or blowing it up. In other words, a disintegrator is not a burninator or a nukinator. Is it possible? Yes. Lasers can be used to break atomic bonds. It is currently very limited. I've seen experiments where lasers have been used to break the atomic bond between hydrogen and silicon. The problem with the current state of technology is that it is focused on very small areas. You want something that spreads out to a large object. There's no reason to assume that it is impossible. We just aren't anywhere close to doing that yet. I personally hope we are never at the point that disintegrating objects at an atomic level is a good idea. 135.84.167.41 (talk) 13:47, 27 December 2019 (UTC)

I think it's useful to analyze this because it helps one understand real-world science. Irrespective of how it's done, to unbind any stable atomic nucleus, you need to add energy to it. This means you need a source of energy and some way to transfer it to the nucleus. No real-world process is perfectly efficient, so some waste heat will always be generated, and this heat has to go somewhere. Additionally, unless you can come up with some technology that's indistinguishable from magic, where you effectively say, "Hey, energy, go excite these nucleons," the energy will be distributed across all the degrees of freedom of the system you add it to. If you go pew-pew at, say, a tank, a bunch of the energy gets "wasted" exciting electrons and molecular and metallic bonds in the substances comprising the tank, rather than going to exciting the nucleons of the atoms. This energy then gets rapidly transferred to the surrounding things, such as air, and also to the photons that these particles radiate as black-body radiation, as the system seeks equilibrium. Energy doesn't just "go away" once you're done with it. This means that barring some really exotic physics, any "disintegrator" weapon would not be terribly different from a very powerful bomb explosion. There could be some benefits in being able to direct the weapon energy more precisely, but you're not going to get a Buck Rogers raygun that you can just zap at something next to you and have it vanish with no effect on the surroundings. (This is echoing some of what NonmalignedNations wrote below.) --47.146.63.87 (talk) 02:03, 28 December 2019 (UTC)

A major flaw in science fiction weapons is that they cause a disintegrated object to simply disappear. Due to conservation of mass the mass will remain the same, whatever the form, or be converted into a massive amount of energy, due to mass energy equivalence. Either would be dangerous to everyone nearby, due to the explosion of all that vapor or all those particles. NonmalignedNations (talk) 14:10, 27 December 2019 (UTC)

I always presumed it was vaporized into subspace or some other convenient "dimension". 89.172.38.89 (talk) 18:06, 27 December 2019 (UTC)

Or at best, collapse into a pile of goo. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:26, 1 January 2020 (UTC)

I would note these assume that these and the above answers by 47 and 135 seem to assume the sci-fi disintegrators/vaporisers are not simply "burninator" which I don't think is always that clear. If the disintegrator/vaporiser is simply magically perfectly burning the body, then the mass goes into carbon dioxide, water etc then you don't have to worry about mass energy equivalence and the massive amounts of energy that will result. You still have practical issues like the inrush of oxygen needed and then what happens to the conversion products since you never seem to see any wind, even if we put aside the impossibility of the process in the first place, but I think it does highlight that there doesn't seem to be any reason to assume that disintegrators/vaporises work by breaking things apart at the atomic level or literally disintegrating things and so those are the problems we need to consider. Nil Einne (talk) 05:54, 1 January 2020 (UTC)

Zapping something with a laser strong enough to ionize it into plasma is sort of what you want, but the amount of laser power required to do that to more than milligrams at a time would likely blind everyone in the vicinity and the hot plasma would ignite anything flammable nearby, and at kilogram quantities result in toxic levels of ozone, nitrogen oxides, and other volatiles and gasses. Tattoo removal lasers will give you an idea of the issues at the million watt range. EllenCT (talk) 04:17, 2 January 2020 (UTC)