What is the net charge and why does it matter?

[CURIE WILLEY]

You are overlooking a subtlety in the definitions. Electric charge is a property of the matter that makes up a system, whereas net charge is a property of the system. It is possible for a zero-net-charge system to be assembled out of pieces of matter that are charged, and depending on the arrangement of charges within the system, there may be a non-zero electric field around the system.

Thank you for the reply Sir.

Isn't system also made up of matter?

Then, how does it make difference in saying charge is a property of matter and net charge as a property of system.

I think both are one and same. The difference is one is made of single particle, so the word charge is associated with it. And the other is made of many particle, so the word net charge. If I am wrong, correct me, Sir.

 

[gmax137]

What is electric charge?
Electric charge is the physical property of matter that causes it to experience a force when close to other electrically charged matter.

So, if the particle has electric charge, there is an electric field around it.

Yes, but then you go on to conclude that if there is a field, then there is "a" charge producing it.

That is just faulty logic.
If A, then B does not imply that if B, then A.

I think this logical fallacy is at the root of your concern.

So what is producing the dipole field? A collection of charges, which happens to sum to zero net charge.

 

[CURIE WILLEY]

This statement is completely wrong. If you want to progress, you'll have to accept that you are wrong, and try to understand why.

Take a system made up of $n$ point charges $q_i$ located at positions $\mathbf{r}_i$. The net charge of the system, as ZapperZ pointed out, is
$Q = \sum_i q_i,$
whereas the electric dipole moment is
$\mathbf{p}(\mathbf{r}) = \sum_i q_i (\mathbf{r}_i - \mathbf{r}).$
Clearly, you can have $Q=0$ while $|\mathbf{p}| \neq 0$. Indeed, take two charges with $q_1 = -q_2$, with $\mathbf{r}_1 \neq \mathbf{r}_2$, and this is exactly what you get.

Even if the configuration of charges is such that the net charge and dipole moment are zero, you can still have non-zero higher moments, such as the quadrupole.

Do you agree this dipole equation?
$E=\frac{1}{4\pi\epsilon}.\frac{p\sqrt{3\cos^2\theta+1}}{r^3}$

Do you agree that electric field around the dipole exists if and only if distance between the charges is zero (i.e p=2aq, 2a is the distance between charges.)?

Note that dipole is not a particle, it is a system of two particles. When distance becomes zero, field will be zero, so net charge (not sum of charges) will be zero. When distance between charges is not zero, net charge will not be zero, but still sum of charges will be zero.

In your above calculation, sum of charges is always zero. But net charge will be zero if and only if distance between charges is zero i.e according to you, when$\mathbf{r}_1 = \mathbf{r}_2$ . This is the reason why I am disagreeing your calculation.

Whether I must be wrong or the other case. I can't run without accepting the reality. I think we have a difference in understanding the concept of net charge.

According to me, sum of the charges will always be zero. But, net charge will be zero if and only if distance between the charge is zero. I think there is a distinction between net charge and sum of charge.

Do you agree this, Sir?
If you explain this, I think I will get my misunderstanding off or we would get some conclusion.

Anyway, sorry for not being under discussion from here on wards as I am preparing for exams tomorrow. I will be active by tomorrow. Thank you for giving your precious time.

 

[Doc Al]

Do you agree this dipole equation?
$$E=\frac{1}{4\pi\epsilon}.\frac{p\sqrt{3\cos^2\theta+1}}{r^3}$$

OK.

Do you agree that electric field around the dipole exists if and only if distance between the charges is zero (i.e p=2aq, 2a is the distance between charges.)?

You have that backwards. That field exists if the distance between the charges is non-zero.

Note that dipole is not a particle, it is a system of two particles. When distance becomes zero, field will be zero, so net charge (not sum of charges) will be zero. When distance between charges is not zero, net charge will not be zero, but still sum of charges will be zero.

No. The net charge, which is just the sum of the charges, will be zero for all distances.

In your above calculation, sum of charges is always zero. But net charge will be zero if and only if distance between charges is zero i.e according to you, when$\mathbf{r}_1 = \mathbf{r}_2$ . This is the reason why I am disagreeing your calculation.

How in the world do you deduce this?

Whether I must be wrong or the other case. I can't run without accepting the reality. I think we have a difference in understanding the concept of net charge.

That's for sure.

According to me, sum of the charges will always be zero. But, net charge will be zero if and only if distance between the charge is zero. I think there is a distinction between net charge and sum of charge.

That's nonsense. Net charge means the sum of the charges. Nothing more.

 

[Ahsan Khan]

As posted previously, definition of charge says, Electric charge is the physical property of matter that causes it to experience a force when close to other electrically charged matter. If we say dipole has no net charge, it can't experience any force, if we keep it near electrically charged matter. I hope, dipole (if distance between charges is not zero) experiences force when kept near charged matter. So, I disagree the statement of dipole having zero net charge. Correct me, if I am wrong Sir.



I should agree your statement also. There is one positive and one negative charge. If we add, we get zero. But, it contradicts the definition of electric charge according to my explanation above. If you say I am wrong, you are indirectly proving definition of charge as incorrect (If my explanation above is agreed by you). In order to make the definition of charge not getting violated and even the rule of algebra, I think we can add or subtract charges if and only if the distance between them is zero. Correct me if I am wrong, Sir.

I should say charge is the fundamental properties of 'some sub-atomic particles' not of matter so a decision if a body is having charge or not, is established by analysing the sub-atomic particles it contains.

Since charge is the property of some sub-atomic particles( due to which it exerts force on other sub-atomic particle(s) carrying same property) and is not the property of matter(in bulk), some sub-atomic particles have this property they are called electrically charged and those sub-atomic particles which lack this property are called neutral. So it is only the sub-atomic particles which have charges. And this property of them is so fundamental that you can not snatch it(property) from them or transfer it to some,different body. Remember charge can neither be created not it can be dystroyed. We can not add(or inculcate) properties of charge in any sub-atomic particle.

What most you can do is to transfer these particles(along with there properties of charge) into other body so that it also starts showing electrical interaction. And we start saying that the body is 'charged'. But here the word 'charged' is used in a sense that it is tonned(or filled) with sub-atomic particles( which are actually the particles for which the definition of charge is applicable). And if a body is tonned with such particles(that is we 'charged' it with what is called charge doesn't mean this body falls in the cateogory of charge because charge is exclusively the properties of sub-atomuc particles. If you carefully look at the defintion of electric charge you will,yourself find that it is the properties of sub-atomic paeticles only. See it and read carefully what is said, you will get your answer.


I will add: TRUE OR FALSE
1). A neutral sub-atomic particle can have electric field. FALSE
2). A neutral object can't have electric field. FALSE

 

[sophiecentaur]

Double negatives are too much like hard work.

I think the problem that ovais has been having is not knowing what the simple word "net" means.

 

[Doc Al]

Double negatives are too much like hard work.

I think the problem that ovais has been having is not knowing what the simple word "net" means.

I think you meant CURIE WILLEY, not ovais.

 

[sophiecentaur]

Yes, I did mean CURIE WILLEY. Sorry, ovais.

This thread is what we get when one person is determined to hang onto the literal meaning of one badly worded phrase at all costs, rather than trying to get to the intended meaning of it. If CURIE WILLEY spent as much time reading around this as he / she has spent arguing, then he / she would have a reasonable understanding of it all by now.

 

[CURIE WILLEY]

You have redefined the meaning of 'zero net charge'. You think it means "there is no field"; all it really means is that the total charge is zero.

You seem to think that something with zero net charge is equivalent to something with no charges at all and thus no fields. Not so.


Wrong.

Since you are so confused about what "net" means, I wonder what you think of an object that experiences a net force of zero. Do you think that that implies there are no forces acting on it?

According to you, if the system is neutral, still there can be electric field around it. Isn't it,sir?

According to me, if the system is neutral, there exists no electric field around it.

According to coulombs law, force between the charges is given by the equation

$F=\frac{1}{4∏ε}.\frac{q_1q_2}{r^2}$

If $q_2$ has net charge zero, it can't exert force on other charge according to me, because it has no electric field around it.

If $q_2$ has net charge zero, it can exert force on other charge ($q_1$) according to you. So, force in the above equation should be non-zero according to you. But, in the equation if you substitute $q_2=0$ F =0, it is not non-zero. This concludes that there will be no field around a neutral object.

Coulombs law is only applicable for point charges, the reason I know is that, if charges is not assumed to be points, charge distribution will not be uniform. In the above case I have assumed to be system of two charges to be $q_2$. Then, we need to assume that charge has uniformly distributed over $q_2$, then we have overcome problem of point charge. Now, I hope my explanation holds good. If it is wrong. Pardon me, sir. And please explain how it is wrong. Moreover, in problems of coulombs law, we will have $q_2$ to be more than charge of electron, indicating it is applicable for system of charges (if charge distribution is uniform).

 

[Cthugha]

According to you, if the system is neutral, still there can be electric field around it. Isn't it,sir?

According to everyone else who posted here besides you, too.

According to me, if the system is neutral, there exists no electric field around it.

You are wrong here. That has already been pointed out.

If $q_2$ has net charge zero, it can exert force on other charge ($q_1$) according to you. So, force in the above equation should be non-zero according to you. But, in the equation if you substitute $q_2=0$ F =0, it is not non-zero. This concludes that there will be no field around a neutral object.

This has nothing to do with applying Coulomb's law. Substituting $q_2=0$ means that you have no charges at all. For a system with no NET charges, you need to apply Coulomb's law for every single charge inside your system which makes up the net charge of zero. It only takes 5 minutes of time to do the math yourself for a simple dipole and you will see that a vanishing force for systems containing more than one charge is actually the exception because the distances from each point charge inside your system to every point outside your system differ slightly. That will happen only if all the charges are precisely at the same position. Just go and do the math. It is trivial.

Coulombs law is only applicable for point charges, the reason I know is that, if charges is not assumed to be points, charge distribution will not be uniform. In the above case I have assumed to be system of two charges to be $q_2$. Then, we need to assume that charge has uniformly distributed over $q_2$, then we have overcome problem of point charge. Now, I hope my explanation holds good.

No, it is not good. It simply does not describe an atom or a dipole or anything interesting, jst charges placed at the same position. This does not describe anything that happens in reality. And by the way you can apply Coulomb's law for inhomogeneous charge distributions. There is no problem with that.

 

[CURIE WILLEY]

Substituting q2=0 means that you have no charges at all

.
Thank you for the reply, Sir. In my explanation, I have considered q2 as system of charges. Thus, q2=0 means net charge as zero. In coulombs law equation, for using q2 as system of charges I have given explanation below that post. For that, I didn't understand your reasoning for disagreeing it. For inhomogeneous charges we consider integration. If I am wrong, pardon me and explain Sir.

 

[Cthugha]

.
Thank you for the reply, Sir. In my explanation, I have considered q2 as system of charges. Thus, q2=0 means net charge as zero.

No. It does NOT mean that. You can ONLY enter the net charge of the system as q2 if they all are exactly at the same position. This is not happening in any real system. To apply the law correctly, you need to apply the law for every single charge in your system. If you have a positive and a negative charge in your system, you apply the law once with -e for q2 for the negative charge and once with +e for q2 for the positive charge. Then you sum up the two forces you get for every position. This will only give you zero net force if the two charges are at exactly the same position. Otherwise the force will not be zero at every position.

 

[sophiecentaur]

@ CURIE WILLEY
I have +1 Couomb on one hand and I have -1 Coulomb in the other hand. By 'your definition', what is my net charge?
(I have very strong arms.)

 

[chingel]

Coulomb's law is not applicable to an arbitrary system with uniform charge distribution. You have to use point charges and if you do that the electric field will not be generally zero. Therefore your reasoning is wrong and objects with zero net charge may generate electrical fields.

 

[CURIE WILLEY]

@ CURIE WILLEY
I have +1 Couomb on one hand and I have -1 Coulomb in the other hand. By 'your definition', what is my net charge?
(I have very strong arms.)

Thank you for the reply, Sir. Please behave well. I may be wrong anywhere, explain why I am wrong. Instead don't use rude language (hate speech).

 

[sophiecentaur]

Thank you for the reply, Sir. Please behave well. I may be wrong anywhere, explain why I am wrong. Instead don't use rude language.

What "rude language"? Are you offended by the Inverted Commas?
I am asking a very short and straightforward question. If you can't answer it then you need to rethink your ideas.

 

[Doc Al]

Thank you for the reply, Sir. Please behave well. I may be wrong anywhere, explain why I am wrong. Instead don't use rude language.

Why don't you just answer the question? No one's being rude. (And your error has been explained several times over!)

 

[CURIE WILLEY]

@DOC AL. Thank you for the reply, Sir. If we have +1 charge in one hand and -1 charge in the other hand, net charge will not be zero (as distance of separation is not zero). In that case, according to me, we need to calculate the electric field created by that dipole at any point, which is at distance r from the center of dipole (we can calculate this from the equation I have given at the begining). By substituting the obtained values of r and E in the electric field produced by a charge equation, we get q value (i.e net charge).

Here, I am not arguing myself to be correct. I am just clarifying my doubts. If I have not behaved well anywhere, pardon me. I will be replying until I get satisfactory result. You may be correct, but I may not be getting your ideas. I hope you will answer me, until I get clarified. Thank you.

 

[sophiecentaur]

@DOC AL. Thank you for the reply, Sir. If we have +1 charge in one hand and -1 charge in the other hand, net charge will not be zero (as distance of separation is not zero). In that case, according to me, we need to calculate the electric field created by that dipole at any point, which is at distance r from the center of dipole (we can calculate this from the equation I have given at the begining). By substituting the obtained values of r and E in the electric field produced by a charge equation, we get q value (i.e net charge).

Here, I am not arguing myself to be correct. I am just clarifying my doubts. If I have not behaved well anywhere, pardon me. I will be replying until I get satisfactory result. You may be correct, but I may not be getting your ideas. I hope you will answer me, until I get clarified. Thank you.

OK, that is your problem. Charge is not a function of position. You are still hanging in on to that statement you started the thread with, which is incorrect. Saying you read it on Wiki, is no justification for it. You will need to let that go, I'm afraid. or launch down your own road towards a different version of Physics. PF will not be following you there.

You are trying to apply blind logic to a faulty premise. You need a more reasonable approach or you will get nowhere.

 

[Cthugha]

@DOC AL. Thank you for the reply, Sir. If we have +1 charge in one hand and -1 charge in the other hand, net charge will not be zero (as distance of separation is not zero).

That does not matter. Draw a circle around your system and count all the charges inside. The number you get is your net charge and here it is zero. The position or separation does NOT matter. This is your very own definition nobody else uses. You cannot expect people to help you if you make up your own language.

 

[Ahsan Khan]

According to you, if the system is neutral, still there can be electric field around it. Isn't it,sir?

According to me, if the system is neutral, there exists no electric field around it.

Wrong. A system of charge may or may not have an electric field around it. As said charge is the exclusive property of (certain) sub-atomic particles not a property of matter in bulk. Charge is such a fundamental property that you can not remove or add this property to anything, what you can only do is to transfer the charge to it other bodies and we say it is charged or toned with or filled with charge. The body just have charge(sub-atomic) particles but itself doesn't become charge(or a collection of charge) as the definition of charge fits only for (certain) sub-atomic particles(like electron and proton).

Accrding to coulombs law, force between the charges is given by the equation

$F=\frac{1}{4∏ε}.\frac{q_1q_2}{r^2}$

If $q_2$ has net charge zero, it can't exert force on other charge according to me, because it has no electric field around it.

Coulombs law is valid only for point charges not for group of charges.

 

[CURIE WILLEY]

@DOC AL. Thank you for the reply, Sir. If we have +1 charge in one hand and -1 charge in the other hand, net charge will not be zero (as distance of separation is not zero). In that case, according to me, we need to calculate the electric field created by that dipole at any point, which is at distance r from the center of dipole (we can calculate this from the equation I have given at the begining). By substituting the obtained values of r and E in the electric field produced by a charge equation, we get q value (i.e net charge).

Here, I am not arguing myself to be correct. I am just clarifying my doubts. If I have not behaved well anywhere, pardon me. I will be replying until I get satisfactory result. You may be correct, but I may not be getting your ideas. I hope you will answer me, until I get clarified. Thank you.

I must add here, as sophiecentaur Sir noted, we can see that for different value of r, we get different value of net charge. For the observer at infinity, net charge of the system will be zero. For the observer near the system the net charge will be maximum.

 

[Ahsan Khan]

What is electric charge?
Electric charge is the physical property of matter that causes it to experience a force when close to other electrically charged matter.

Wrong. I guessed here the key problem is your wrong understanding about the fundamental of charge. Charge not the property of matter(in bulk) it is the property of(certain)sub-atomic particles(like,electron, proton etc). Charge is not a substance rather it is property of certain sub-atomic particles just as mass is the property of any matter charge is also a property. You can add mass to a body what you only can do is to add matter(having property of mass) so that they get weighed. But by doing this you can not call matter as mass matter and mass is different. And definition of mass should not be applied to matter in any case.

So, if the particle has electric charge, there is an electric field around it.

Yes offcourse, but for this it must be a particle(or better I call a sub-atomic particle like electron).

 

[CURIE WILLEY]

OK, that is your problem. Charge is not a function of position.You are still hanging in on to that statement you started the thread with, which is incorrect. Saying you read it on Wiki, is no justification for it. You will need to let that go, I'm afraid. or launch down your own road towards a different version of Physics. PF will not be following you there.

Thank you for replying and being cooperative, Sir. As the discussion has followed, definition (charge or neutral particle) of wiki has been said to be wrong. If correct definition is provided, it will be greatly appreciable. This decides whether I am launching a new road towards a different version of Physics or not, or PF will be following me or not.

You are trying to apply blind logic to a faulty premise. You need a more reasonable approach or you will get nowhere.

I will try to bring brightness where there is blind logic, please provide info on where there is blind logic.

 

[Ahsan Khan]

According to me, sum of the charges will always be zero. But, net charge will be zero if and only if distance between the charge is zero. I think there is a distinction between net charge and sum of charge. [/B]

If you think there is a distinction(which you have created by your own and offcourse you can, but society of science has already made these two terms alike and probably they are not going to change for you) then read Gauss Law which talks about net charge enclosed by a body. And it says the flux linked by Gaussian surface is proportional to the NET CHARGE contained in it. And in the calculations to find net charge you just need to take algebraic SUM OF THE CHARGES, distance between them does not affect the net charge.

 

[CURIE WILLEY]

That does not matter. Draw a circle around your system and count all the charges inside. The number you get is your net charge and here it is zero.

I have replied, why I don't agree net charge is zero here. Please read it, if you find I am wrong there, pardon me and explain where I am wrong.

The position or separation does NOT matter. This is your very own definition nobody else uses. You cannot expect people to help you if you make up your own language.

If you think I have created my own definition, please specify which one I have created. And please provide correct definition for it (with reference, from where you have got that definition).

 

[Doc Al]

@DOC AL. Thank you for the reply, Sir. If we have +1 charge in one hand and -1 charge in the other hand, net charge will not be zero (as distance of separation is not zero).

False. Until you correct this statement, there's not much point of going any further. The net charge will be zero regardless of the distance.

 

[Ahsan Khan]

According to coulombs law, force between the charges is given by the equation

$F=\frac{1}{4∏ε}.\frac{q_1q_2}{r^2}$

If $q_2$ has net charge zero, it can't exert force on other charge according to me, because it has no electric field around it.

Yes if q2 is not exerting force then it can never be charged PARTICLE(remember you are saying it on the basic of Coulomb's law which is valid for point charges). But what if this is not a point,sized charged particle but a collection of charged particles(like dipole or hydrogen atom- on which you are trying to apply the definition of charge while they are not charge, for charge is exclusively the property of a(certain sub-atomic) particles you should not apply it for collection of charge))or matter with charge particles.
Do you think Coulomb would allow to use his law under such case?

 

[CURIE WILLEY]

@DOC AL. Thank you for the reply, Sir. If we have +1 charge in one hand and -1 charge in the other hand, net charge will not be zero (as distance of separation is not zero).

False. Until you correct this statement, there's not much point of going any further. The net charge will be zero regardless of the distance.

If distance of separation between the opposite charges of the dipole is zero, electric field around the system will be zero. As said always, according to me, if field is zero, net charge is zero. If distance of separation between the opposite charges is non-zero, there exists field. So, according to me, if field is non-zero, net charge is non-zero.

This has been disagreed, saying definitions of wiki is wrong. If they are wrong, it would be appreciable if correct definitions are provided (with reference, from where that definition has been extracted).

I think we are in need of knowing what actually is net charge?

So, if any particular definition from any particular reference would be appreciable. I have provided my opinion on the basis of wiki, but they are said be incorrect. So, there is a need of knowing correct definitions.

 

[ZapperZ]

Closed, pending moderation.

Zz.

 

[Dale]

This has been disagreed, saying definitions of wiki is wrong. If they are wrong, it would be appreciable if correct definitions are provided (with reference, from where that definition has been extracted).

I think we are in need of knowing what actually is net charge?

The definition of net charge was given by Doc Al in post 10.

Net charge being zero simply means that the total charge (just add 'em up) is zero: $\Sigma q_i = 0$

For references there are the following academic links:
http://www.physics.sjsu.edu/becker/physics51/elec_charge.htm
http://web.mit.edu/viz/EM/visualizations/coursenotes/modules/guide02.pdf

Although it should be obvious. The term "net" simply means the sum. So your "net income" is the sum of all of your sources of income less any deductions to your income. Similarly, "net force" on an object is the sum of all forces acting on the object. Similarly, "net charge" is the sum of all the charges.

Note that $E=k\Sigma (q_i/r_i^2) \mathbf{\hat r}$ can be non-zero even if $\Sigma q_i$ is zero. Your reasoning is simply wrong, as was pointed out to you many times.