What do we mean when we say that charge is moved or transfered

[SHASHWAT PRATAP SING]

Electric Charge is the characteristic property of subatomic particles that causes it to experience a force when placed in an electromagnetic field.
So, if electric charge is a characteristic property of subatomic particle then-

what do we mean when we say charge is transferred from one body to other ?
Also, giving a neutral body electric charge makes the body negatively charged and taking electric charge from a neutral body makes it positively charged.

Now, what does this mean as if electric charge is a characteristic property of subatomic particles then how can a property be moved or transffered from one body to another.Also, how can we give a property to a neutral body,as electric charge is a property so how can it be moved or gived ?

Also, what does it mean a neutral body contains charges but they are balanced.

How can a property be balanced and how can a body contain a property as electric charge is a characteristic property ?
Please help me.

 

[Doc Al]

Now, what does this mean as if electric charge is a characteristic property of subatomic particles then how can a property be moved or transffered from one body to another.Also, how can we give a property to a neutral body,as electric charge is a property so how can it be moved or gived ?

When you transfer charge to a body, you are adding (or removing) charged particles (usually electrons). You're not changing the properties of subatomic particles.

 

[SHASHWAT PRATAP SING]

When you transfer charge to a body, you are adding (or removing) charged particles (usually electrons). You're not changing the properties of subatomic particles.

Doc Al so when we say charge is moved from one body to other this means that --
electron is being moved from one body to another as electron has the property of charge.

But, then why do we say this as charge is moved from one body to other, we should say electron is being moved from one body to another ? why do we say charge is moved if its the property of electron.

 

[Doc Al]

But, then why do we say this as charge is moved from one body to other, we should say electron is being moved from one body to another ? why do we say charge is moved if its the property of electron.

Often all one cares about is the total charge transferred to the body. You could speak of electrons being transferred, but it's easier just to talk about the charge transferred. (Electrons are tiny and have little mass.)

But you are correct: When "charge" is moved, what's really moved is charged particles.

 

[A.T.]

But, then why do we say this as charge is moved from one body to other, we should say electron is being moved from one body to another ?

Both is correct, and it depends on the context what you want to to emphasize.

 

[SHASHWAT PRATAP SING]

Both is correct, and it depends on the context what you want to to emphasize.

But, A.T. isn't this weird saying "charge is moved" as it's a property of electron so how can a property move from one body to other ?
Infact, we should say electrons move from one body to other and they have the characteristic property of charge.
So, when we say electron is moved it would be clear that electric charge is carried by electron.

 

[A.T.]

But, A.T. isn't this weird saying "charge is moved" as it's a property of electron so how can a property move from one body to other ?

To me it's weird, that you find that weird.

 

[SHASHWAT PRATAP SING]

To me it's weird, that you find that weird.

A.T. I got it.
Whenever we say charge is moved it's actually electron which is moved since electron has the characteristic property of electric charge, so in general we say charge is moving.

But we should keep in mind that When "charge" is moved, what's really moved is charged particles (electrons).

Please tell me am I correct now.

 

[A.T.]

But we should keep in mind that When "charge" is moved, what's really moved is charged particles (electrons).

It doesn't have to be electrons. There are other charged particles. The point of having the abstract quantity charge is that it's more general.

 

[SHASHWAT PRATAP SING]

It doesn't have to be electrons. There are other charged particles.

A.T. please tell me what do you mean by this, I didn't get it.
Please...

 

[A.T.]

A.T. please tell me what do you mean by this, I didn't get it.
Please...

https://en.wikipedia.org/wiki/Charged_particle

 

[SHASHWAT PRATAP SING]

https://en.wikipedia.org/wiki/Charged_particle

A.T. ok I got it.

Whenever we say charge is moved it's actually electron(or any other charged particle according to the condition) which is moved since electron has the characteristic property of electric charge, so in general we say charge is moving.

But we should keep in mind that When "charge" is moved, what's really moved is charged particles .

Please tell me now am I correct ?

 

[A.T.]

But we should keep in mind that When "charge" is moved, what's really moved is charged particles .

Yes. And sometimes missing charged particles (holes) are treated as charge carriers too.

 

[jbriggs444]

But we should keep in mind that When "charge" is moved, what's really moved is charged particles .

No. We should not keep this in mind. It is actually a significant problem for students learning about electricity and magnetism that they fail to think abstractly about charge and instead try to think physically about things like electrons.

 

[vanhees71]

But, A.T. isn't this weird saying "charge is moved" as it's a property of electron so how can a property move from one body to other ?
Infact, we should say electrons move from one body to other and they have the characteristic property of charge.
So, when we say electron is moved it would be clear that electric charge is carried by electron.

Well, charge is an intrinsic property of the particles and thus is transported when the particle is moving.

 

[f95toli]

No. We should not keep this in mind. It is actually a significant problem for students learning about electricity and magnetism that they fail to think abstractly about charge and instead try to think physically about things like electrons.

I agree, the example of holes has already been mentioned, but in solid state physics there are also many other quasiparticles where you shouldn't think of charge transport as "physical particles" moving.
Note that you e.g. also have quasiparticles with fractional charge (i.e less than e).

 

[vanhees71]

Well, yes, but the beauty of the quasi-particle paradigm (due to Landau) is that you can think about current as moving charged particles. Of course, in classical electrodynamics it's more appropriate to work in a continuum-mechanical model with charge and current densities, and the simple constitutive laws used within the classical theory become very intuitive when thinking in such "fluid-dynamical pictures". The phenomenological result of these (of course oversimplified) classical models of matter (like the Drude model for electric conductivity of a metal or the classical dispersion theory for a dielectric assuming the bound charges as harmonically bound at their equilibrium position and being slightly perturbed by application of an external electromagnetic field) is amazingly correct, if you accept that several parameters of the medium have to be taken from measurements and cannot be predicted within a classical model. To also predict the parameter, of course you need quantum many-body theory as studied in condensed-matter physics.

 

[SHASHWAT PRATAP SING]

No. We should not keep this in mind. It is actually a significant problem for students learning about electricity and magnetism that they fail to think abstractly about charge and instead try to think physically about things like electrons.

Sorry jbriggs444, but I didn't get what did you mean by this ?
Please help me.

 

[PeroK]

Sorry jbriggs444, but I didn't get what did you mean by this ?
Please help me.

The theory of classical EM is based on the concepts of charge and EM fields. You can (and should) study the subject using those concepts and not necessarily see it as a theory of charged particles. For example:

In terms of electromagentism, a flow of negative charge in one direction is completely equivalent to the flow of positive charge in the opposite direction. In terms of EM these cases are indistinguishable.

In fact, thanks to Benjamin Franklin, current is seen as a flow of positive charges; whereas, in fact, it's generally negative charges that are moving (electrons). The current convention, therefore, is perhaps the wrong way round, but according to the above equivalence this doesn't matter.

 

[vanhees71]

Well, with help of the Hall effect we can find out whether a current is made up from positively or negatively charged particles.

This works as follows: Take, e.g., a metallic bar $[0,a]\times [0,b] \times [0,c]$ and connect a battery at the sides parallel to the $xy$ plane. Then the current density $\vec{j}=n q v \vec{e}_y$, where $n$ is the number of conduction particles in the bar, $v$ their velocity and $q$ their charge.

Now in addition put a magnetic field $\vec{B}=B \vec{e}_z$. Now Ohm's Law holds, but you have to take into account both the electric and the magnetic force on the particles, i.e., now it reads
$$\vec{j}=\sigma(\vec{E}+\vec{v} \times \vec{B}) = \sigma (E_x \vec{e}_x + E_y \vec{e}_y + v B \vec{e}_y \times \vec{e}_z)=\sigma [(E_x+v B) \vec{e}_x + E_y \vec{e}_y] \stackrel{!}{=} \sigma E_y \vec{e}_y.$$
This is in the new steady state of the charges, i.e., you have the same $E_y$ due to the battery as before, i.e., $E_y=U/b$.

Due to the magnetic force on the charged particles, however you have drift in the $\vec{e}_x$ direction such that the surfaces parallel to the $yz$-plane get a surface charge and the corresponding electric field $E_x=-v B=-j B/(n q)=U_{\text{H}}/a$ builds up so that the net force on the charge carriers in $x$ direction is 0 again. Thus you have an additional voltage difference at the two surfaces parallel to the $yz$ plane.

As you see for a given direction of $\vec{j}$ (here we assume it's $j>0$, i.e., the current density is directed in positive $y$ direction). As you see the sign of the Hall voltage $U_{\text{H}}$ depends on the sign of charge of the conduction particles. For electrons $q=-e<0$ and thus $U_{\text{H}}$ is positive in this setup while it were negative if the charge carriers were positive.

The latter case can be realized by certain types of semiconducters where the conduction charges are positive (what's moving in this case are "quasiparticles", i.e., the holes in a sea of electrons, which behave effectively like positive charges).

 

[Helena Wells]

Well, with help of the Hall effect we can find out whether a current is made up from positively or negatively charged particles.

This works as follows: Take, e.g., a metallic bar $[0,a]\times [0,b] \times [0,c]$ and connect a battery at the sides parallel to the $xy$ plane. Then the current density $\vec{j}=n q v \vec{e}_y$, where $n$ is the number of conduction particles in the bar, $v$ their velocity and $q$ their charge.

Now in addition put a magnetic field $\vec{B}=B \vec{e}_z$. Now Ohm's Law holds, but you have to take into account both the electric and the magnetic force on the particles, i.e., now it reads
$$\vec{j}=\sigma(\vec{E}+\vec{v} \times \vec{B}) = \sigma (E_x \vec{e}_x + E_y \vec{e}_y + v B \vec{e}_y \times \vec{e}_z)=\sigma [(E_x+v B) \vec{e}_x + E_y \vec{e}_y] \stackrel{!}{=} \sigma E_y \vec{e}_y.$$
This is in the new steady state of the charges, i.e., you have the same $E_y$ due to the battery as before, i.e., $E_y=U/b$.

Due to the magnetic force on the charged particles, however you have drift in the $\vec{e}_x$ direction such that the surfaces parallel to the $yz$-plane get a surface charge and the corresponding electric field $E_x=-v B=-j B/(n q)=U_{\text{H}}/a$ builds up so that the net force on the charge carriers in $x$ direction is 0 again. Thus you have an additional voltage difference at the two surfaces parallel to the $yz$ plane.

As you see for a given direction of $\vec{j}$ (here we assume it's $j>0$, i.e., the current density is directed in positive $y$ direction). As you see the sign of the Hall voltage $U_{\text{H}}$ depends on the sign of charge of the conduction particles. For electrons $q=-e<0$ and thus $U_{\text{H}}$ is positive in this setup while it were negative if the charge carriers were positive.

The latter case can be realized by certain types of semiconducters where the conduction charges are positive (what's moving in this case are "quasiparticles", i.e., the holes in a sea of electrons, which behave effectively like positive charges).

So I was correct!The hall effect changes the resistance of a conductor!

 

[berkeman]

So I was correct!The hall effect changes the resistance of a conductor!

It is customary to capitalize the names of real people. That includes when their last names are used to name scientific discoveries that they were involved in. So it's traditionally written as the "Hall effect".

 

[vanhees71]

So I was correct!The hall effect changes the resistance of a conductor!

No, why should it?

 

[Helena Wells]

No, why should it?

Because electrons flow from a smaller area of the conductor.

 

[vanhees71]

The electrons (in the stationary state) just flow as without magnetic field in a straight line due to the voltage difference from the battery (see my explicit solution of the Maxwell equations in #20). The resistance is $R=b/(\sigma a c)$.