Talk:Electrostatics

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@Johnjbarton, electrostriction applies to any dielectric, both solid and fluid. It does not need a conductor, and has in most cases an E**2 dependence (P**2 with polarization), although not always. It is not really the same as what is being described in this section, but is a pressure so I believe belongs here as well. I will leave aside things like deformation potential, polar metals and lots of other fun stuff as too complex for here. Ldm1954 (talk) 17:03, 22 August 2025 (UTC)[reply]

Your source does not say that. Johnjbarton (talk) 17:07, 22 August 2025 (UTC)[reply]

I think we could include a sentence to clarify the current puzzling and possibly synthetic comment:

• Note that there is a similar form for electrostriction in a dielectric.

I tried but was reverted, presumably because charges directly on the dielectric would cause electrostriction even though no source is given to that effect.

The source

• Pelrine, Ronald E.; Kornbluh, Roy D.; Joseph, Jose P. (1998-01-01). "Electrostriction of polymer dielectrics with compliant electrodes as a means of actuation". Sensors and Actuators A: Physical. Tenth IEEE International Workshop on Micro Electro Mechanical Systems. 64 (1): 77–85. doi:10.1016/S0924-4247(97)01657-9. ISSN 0924-4247.

Says

• The term electrostrictive is used here in the generic sense to describe the stress and strain response of a material to an electric field. Many researchers (particularly those investigating ceramic materials) reserve the term to refer to the strain response of a material in an electric field that arises from field induced intramolecular forces. Electrostriction is often further distinguished from piezoelectric behavior in that the response is proportional to the square of the electric field, rather than proportional to the field. The electrostriction of polymer dielectrics with compliant electrodes results from the electrostatic forces generated between free charges on the electrodes, and is proportional to the square of the electric field. Since the electrostriction results from external electrostatic forces, any elastomeric dielectric material will exhibit electrostriction by this definition, in theory. Thus, it may be argued that actuators based on this technology are more properly considered to be electrostatic. However, as will be shown, the dielectric and mechanical properties of the polymer material determine the magnitude of the stress and strain response, and so we feel that electrostrictive is a more appropriate description.

The source

• Zimmerli, G. A., Wilkinson, R. A., Ferrell, R. A., & Moldover, M. R. (1999). Electrostriction of a near-critical fluid in microgravity. Physical Review E, 59(5), 5862.

Makes essentially the same point. Johnjbarton (talk) 17:06, 22 August 2025 (UTC)[reply]

I added a source. Please also check electrostriction, since it is about an order of magnitude more important that the "electrostatic pressure". I will check and clarify more tomorrow as I am out of the office this afternoon/evening. Ldm1954 (talk) 17:38, 22 August 2025 (UTC)[reply]

I changed this sentence:

• This pressure acts normal to the surface of the conductor, independent of the sign of the surface charge, charge carriers (i.e. negative for electrons or positive for protons) or normal component of the electric field at the surface.

If I parse it as

• (independent of the sign of the surface charge) or (normal component)

then we are comparing signs to components. It makes more sense parsed this way:

• independent of the sign of (the surface charge) or the sign of (normal component of the electric field)

but the punctuation does not make it clear what it meant. I used

• This pressure acts normal to the surface of the conductor, independent of the sign of the surface charge or, equivalently, to the direction of the normal component of the electric field at the surface.

The source only notes the sign of the surface charge, but gives the field as surface charge times the normal component of the field in the previous sentence. I think it would be clearer simply as

• This pressure acts normal to the surface of the conductor, independent of the sign of the surface charge.

Johnjbarton (talk) 16:54, 25 August 2025 (UTC)[reply]

Two points:

1. It is important to mention that it does not matter whether the carriers involved are electrons, protons, holes etc. There have been a lot of debate and (frankly) weak science. Ignoring this is a disservice to readers. You can check some of the references in Triboelectricity#Electron and/or ion transfer or in Proton conductor.
2. Because the dependence is upon the normal component of the field squared the sign (into or out of) does not matter.

N.B., the equations were wrong, I corrected them. For instance you cannot equate the electric field vector and the surface normal, and later the field dependence was wrong. This is all in Griffiths of course as well as many other texts. Ldm1954 (talk) 17:49, 25 August 2025 (UTC)[reply]

It is important to source claims. That is why I removed the carriers: there is no source for that. If you have sources in the other pages, add them; neither of those pages mention electrostatic pressure so I could do so myself.

You can attribute the reason for the independence to either the field-squared or the attraction of surface charges, these are equivalent. Johnjbarton (talk) 18:11, 25 August 2025 (UTC)[reply]

Sorry John, but you have it the wrong way around. All that is in Griffiths states is "charge", nowhere is this stated as just electrons. Of course there are other free charges than electrons, surely you are not asking for a reference for that!

I do not know what you mean by "attraction of surface charges", I think that is a typo. Ldm1954 (talk) 18:16, 25 August 2025 (UTC)[reply]

N.B., just in case there is ambiguity, the surface charge that Griffiths (and others) talk about has to come from somewhere, so these are free carriers (as against bound charges). Ldm1954 (talk) 18:20, 25 August 2025 (UTC)[reply]

In electrostatics there are no "carriers" its just "surface charge". Electrostatics as subject exist long before electrons/protons as a subject. Griffiths only needs to say "charge", not "electrons" or anything else, they are not relevant to the topic at this point. The modern theory of the cause of surface charge is separate from almost all results in electrostatics. Which is why Griffiths does not discuss "carriers" etc.

I did mean "attraction of surface charges", as nicely illustrated in the diagram in the article section "Electric field". The arrangement of the surface charges is exactly equivalent to the field in electrostatics. Johnjbarton (talk) 22:25, 25 August 2025 (UTC)[reply]

1. As mentioned earlier, for encyclopedic content we should mention that the relevant charge can be anything.
2. That Figure is electrostatic induction, and the equation of relevance is the Coulomb Law boundary condition (aka Gauss, better is the generalized Ampere equation with D, but we don't need to worry about that). Sorry, you have the cart before the horse; the surface charge is there to satisfy the boundary condition of E=0 inside a classical conductor. With the divergence theorem there is an additional term at any boundaries which is the equation in the "Pressure" section.

I have spent a lot of time of getting these details right. You can have a look at https://arxiv.org/abs/2503.01600 if you want some light reading (it is accepted). Ldm1954 (talk) 22:56, 25 August 2025 (UTC)[reply]

Normal to the surface could be inward or outward. Charge has a sign. An electric field has a direction. An electric field des not have a sign, but a component of the field, such as the normal component, can have a sign with respect to a reference such has positive being outward and negative being inward. Constant314 (talk) 05:59, 26 August 2025 (UTC)[reply]

Sorry no, +ve normal to the surface is outwards. Otherwise that is exactly the point being made. It does not matter whether the charge carriers are +/-, the nirmal component is +/-. Ldm1954 (talk) 10:47, 26 August 2025 (UTC)[reply]

We are a serious community. Kaukênteo (talk) 04:26, 27 October 2025 (UTC)[reply]

What is unserious about the picture? Doesn't it give a good real world portrayal of electrostatics? 2001:1C0F:997:6100:EF4D:F9CD:D435:8E4F (talk) 09:18, 27 October 2025 (UTC)[reply]

The cat image is fine. It illustrates the subject of the article well. If it makes people smile then there is no harm in that. Unless there is a demonstrably better image that we should use instead, it can stay. DanielRigal (talk) 13:51, 27 October 2025 (UTC)[reply]

Keep it. The image is in the article by a strong consensus. Constant314 (talk) 15:57, 27 October 2025 (UTC)[reply]

No, the cat shouldn't be replaced, besides of not really having a better exemple of eletrostatic, it help people understand how mudane and common the event is, the cat help to catch people attention. A image of a cat doesn't make wikipedia less serious make it more humane. And in a era where IA is everywhere this type of thing is important. Bonaparte Napoleão (talk) 14:25, 10 November 2025 (UTC)[reply]