Static Electricity electron transfer

1. Jan 15, 2012

nDever

Hey guys,

Most physics or introductory electronics books that I have read begin the topic of electricity by introducing static electricity. The books introduce static electricity by either talking about the amber and the wool experiment or the glass rod and the silk cloth.

My question is, what in fact is going on when the glass rod and the silk cloth are rubbed together and then later, attract? One of the materials involved in the electron transfer must have a net charge correct? What is the difference between electrostatic induction and the triboelectric effect?

2. Jan 16, 2012

Drakkith

Staff Emeritus
3. Jan 16, 2012

nDever

I suppose that my question is more related to the process of charge transferal. How exactly can an electric charge exist between two electrically neutral materials? If the atoms of both materials contain equal numbers of their respective electrons and protons, why would one material accept electrons from the other?

4. Jan 16, 2012

Drakkith

Staff Emeritus
According to the wiki page, it isn't really known how the objects transfer electrons. I know I don't know how. Maybe someone else here has some idea.

5. Jan 17, 2012

sankalpmittal

By experiment we mean that glass rod give electrons and silk cloth take electrons , if we rub the two together. So glass rod develops positive charge and silk cloth negative and thus these two attract each other.

Now I don't think so that you will be satisfied with my answer because your question is that if glass rod and silk cloth both are electrically neutral then how come on rubbing these attract each other ?!

Sir , we have made combinations since prehistoric times like :
Glass rod and silk cloth
Ebonite rod and glass rod
Ebonite rod and cat's fur
Hairs and comb
Balloon and wall
etc.. etc...
One acts positive while one negative..

Rules of charging by friction

Now prediction of positive and negative charges like which of combination will be positive and which will be negative is done by electric series :

cat's fur , flannel , sealing wax , glass , cotton , paper , silk , human , wood , metal , rubber , resin , amber , Sulphur , ebonite ..... in descending order.

If an item x is rubbed with any item higher than it in series then it (x) will be charged negatively by friction else item x will be charged positively. Rest is up to property of the object.

Force of friction or your mechanical energy rips off the electrons from one object to another. In other words the mechanical energy of your hand changes to electrical energy.

See Drakkith's post 2 for your difference between electrostatic induction and the triboelectric effect.

Last edited: Jan 17, 2012
6. Jan 17, 2012

nDever

Although atoms may be electrically neutral, is there still a tendency for them to gain/lose electrons?

7. Jan 17, 2012

Drakkith

Staff Emeritus
It can happen, but it's much more favorable to remain neutral unless it can form some kind of bond with another atom. But even then the molecule is neutral as a whole.

8. Jan 17, 2012

nDever

Ah, I see. So then, lets consider the wool and wax. To start with, the wool and wax are neutral, however, rubbing them together upsets the neutrality (triboelectric effect). The electrons are transferred from the wool to the wax thus causing the wax to have a negative net charge and the wool to have a positive net charge. In other words the wax now has some of the electrons belonging to the wool plus its own.

Now, all that remains is the question of why this happens. Why would the electrons just 'rub off' of the wool like this? After all, they are both neutral to start with.

9. Jan 17, 2012

Drakkith

Staff Emeritus
As said in the article, it isn't currently understood well. Perhaps the friction of rubbing affects the wool differently than it does the wax. I really don't know.

10. Jan 17, 2012

nDever

I do appreciate the explanation.
I suppose something happens on the quantum level.

So then, by speculation, after the wax and wool now have a charge, these things may happen...

- The wax and wool are again contacted, the wool gets its electrons back, thus, a spark is produced and the charge is eliminated.

or

- The wool can get more electrons from some other negatively charged material and the wax can give its excess electrons to some other positively charged material.

11. Jan 18, 2012

sankalpmittal

To explain these phenomenon in more detail we have to go in explanation which will be more of chemistry than physics.

In post 5 , I wrote an electric series. You can call it triboelectric series also. Here is more developed model of that series :

Asbestos
Fur (rabbit) / cat fur
Flannel
Wax
Glass
Mica
Wool
Quartz
Fur (cat)
Silk
Human skin, Aluminum
Cotton
Wood
Amber
Copper, Brass
Rubber
Sulphur
Ebonite
Celluloid
India rubber

I also wrote that if an item x is rubbed with any item higher than it in series then it (x) will be charged negatively by friction else item x will be charged positively. Lets make it easy. Higher one in series will be positive charge and lower one negative if two are rubbed together.

Consider that wool is rubbed with wax. Since wax is higher than wool in the series so wool will be charged negatively and wax positively and these two will attract each other , right ?

Now if you go back to chemistry ionization level then ask yourself how an atom of sodium ionizes itself and so is chlorine atom although initially they are electrically neutral ? (say)

Sodium looses electrons and chlorine takes electrons though initially they are neutral , because sodium gains energy - heat energy , by percussion etc which forces the electrons in its outermost orbital to become free. Now chlorine has high nuclear force , so it easily takes electrons and loose energy due to the law of conservation of energy. Getting it ?

Sodium + energy -> Sodium positive ion + 1 electron
Chlorine + 1 electron -> Chlorine negative ion + energy
Sodium positive ion + Chlorine negative ion -> Sodium Chloride

Now lets go back to physics level :

When we rub wax and wool we apply mechanical energy which rips off the electrons from outermost orbital of wax atom and it gains positive charge. Before there can be conduction of charge the , high nuclear force of wool atom attracts electrons lost by wax and hence wool gains negative charge by taking electrons lost by wax. If we go into detail then wax is more metallic in nature and wool more non metallic. If we rub wool with asbestos then wool will be negative and asbestos positive because asbestos is more metallic than wool. Nuclear charge of wool > asbestos , also.

After all it has the property like this !!!! Wool rubbed with wax.. Wool atom gains electrons easily because electrons in its outermost shell are strongly bound due to high nuclear force.
Wax looses electrons easily because electrons in its outermost/valence shell are loosely bound. We can deduce it like this. So now you got your answer ? We can also deduce that size of wax atom > size of wool atom.. You must have knowledge of chemistry to make such deductions.

That's all. Hope this helps.
:)

Last edited: Jan 18, 2012
12. Jan 18, 2012

nDever

Yes, thank you; I understand now. Actually, I researched a bit and found the cause of the tendency for atoms to gain or lose electrons and I found that different atoms and molecules have a property called electron affinity. Chemical species with higher electron affinity have a higher tendency to receive electrons from species with lower electron affinity. I have come to the conclusion that electrons just move; They move whether the atoms or molecules that they orbit are charged or not.

I understand how atoms attain charge now. For discharging and ground...

When exactly will a charged object be discharged? I know that an object will discharge when a conducting path is made to an object with an opposite charge. Is this the only time?
Is it possible for a charged object to regain electrical balance with a neutral object or will the neutral object just be polarized?

Exactly what qualifies an object to be a ground?

13. Jan 19, 2012

sankalpmittal

Actually I did not mention the terms like Ionization potential , electron affinity , etc.
Let me make it a bit more comprehensive.

Asbestos
Fur (rabbit) / cat fur
Flannel
Wax
Glass
Mica
Wool
Quartz
Fur (cat)
Silk
Human skin, Aluminum
Cotton
Wood
Amber
Copper, Brass
Rubber
Sulphur
Ebonite
Celluloid
India rubber

Ionization potential and Size of atom of substances decreases as we go down this series and increases as we move up.
(Ionization potential is energy required by an atom to loose electrons from its valence shell)

Electron affinity , Electronegativity and Nuclear charge of substances increases as we go down this series and decreases as we move up.

(Electron Affinity is the energy lost by an atom if it gains electrons)
(Electronegativity is the tendency of an atom to attract electrons towards itself while forming a kind of bond.)

Chemistry level explanation : Yes , I think this is the only time because elements being reactive cannot loose or gain electrons after they form ions. Example: Na+

Physics Level Explanation : Suppose silk cloth is charged negatively. Then leaving it for a time it will be discharged automatically because such substances easily loose or gain electrons into or from atmosphere and also surroundings. So your statement does not hold true for physics. Its only true for chemical elements.

If you bring a charged object towards neutral object then
Neutral object will develop opposite charge if charged object is brought near it but not in contact. Process is induction.
[ii] If charged object is kept in contact with neutral one then neutral object attains same kind of charge as charged one. Process s conduction.

I think that charged object cannot regain electrical balance with a neutral object. Its not always possible that oppositely charged objects attract. There has to be strong bonding force. Yes suppose if comb rubbed with hair attract paper pieces then after paper pieces are attracted , overall system will be neutral. Law of conservation of charge. It does not mean that papers are neutral then or comb !

Yes, neutral object will be polarized but its not necessary that it will attract or be attracted towards charged object.

Huh ?
Connect a charged object via a conductor to earth. Hence object will be ground or earthed. It will again be neutral. Every object can be ground if its connected via a conductor to earth.

14. Jan 19, 2012

nDever

Let me show you my sources.

This is where I am learning about static electricity as a whole.
http://www.physicsclassroom.com/Class/estatics/

This is where I learned about electron affinity.
http://www.physicsclassroom.com/Class/estatics/U8L2a.cfm

This is where I learned about ground.
http://www.physicsclassroom.com/Class/estatics/u8l2d.cfm

15. Jan 19, 2012

sankalpmittal

Yes.. So ?

This is what I typed in my previous post !
Again read my previous post if you haven't. In case if you have , then read it again.

Best of Luck !

16. Jan 19, 2012

nDever

I just wanted to know as much as I can about static electricity on an atomic level. There are so many facts that need to be considered in this topic. It is difficult to predict what happens in certain given situations.

Positive, negative, neutral;
Conductors, insulators, semi-conductors;
Induction, Contact-induced, charge-induced...

I guess I'll get it eventually...

17. Jan 21, 2012

sankalpmittal

Hmmmm , what is still not clear ? What is confusing you ? In post 13 , I answered the questions which you asked. Are you not satisfied with them ? Is so then please notify... Or you have some other questions to ask.. If so then do please ask... Or you cannot understand them.. If so then I can make you understand them , the other way... That is what I can tell repeatedly.

What do you need to ask ? May be I can help you ?... or not ?

And please I am not any kind of "encyclopaedia or source of knowledge" who keeps on tutoring you lesson wise. If you have doubt then please do ask particular question. You seem to be asking that :- "Please can you tell me about static electricity as much as you can ?"

I think no one can.. Just google it and if any part or sector you do not understand then please ask...

Here , these sites will provide you with good insights about static electricity at atomic level :