Understanding Electromagnetism: Clarifying Concepts for Class 10th Students

[Simon Bridge]

Yeah - if you wanted to have a different current direction for each charge. And what was the expected gain again? It may not confuse students as much? Wasn't that it?

 

[sankalpmittal]

You are right, and it would be even more complicated than that in many circumstances. For instance, in electrolytes you would have both left handed fields from the negative charge carriers and simultaneously you would have right handed fields from the positive charge carriers. This is important for pacemakers, neuro-prosthetics, transcranial magnetic stimulation, and magnetoencephalography. You would run into similar problems studying plasmas like the sun.

It would be a simple change of convention to make electrons be positively charged. But regardless of your convention for the charge of an electron, it is important that current point in the opposite direction of the motion of negative charge carriers. Keeping in mind that despite the fact that electrons are the charge carriers in metal there are always going to be some circumstances where protons are charge carriers that you need to deal with also.

Yeah - if you wanted to have a different current direction for each charge. And what was the expected gain again? It may not confuse students as much? Wasn't that it?

Not sure what people mean by charge flow in electric circuits ?
Here are certain sites which point out that current flow from positive to negative in reality in DC. Can you grasp little bit of it ? I find it quite sophisticated. How can charge flow in an electric circuit ? Please tell.

I find excellent bunch of sites which claim that current flows from positive to negative due to back attraction. In other words , it agrees with DaleSpam.

1. http://amasci.com/amateur/elecdir.html
2. http://www.asmcommunity.net/board/index.php?topic=12847.0
3. http://forum.allaboutcircuits.com/showthread.php?t=32202
4. http://amasci.com/miscon/eleca.html#frkel

Originally quoted by www.amasci.com/miscon/eleca.html#frkel :

I try to take my own advice: I always imagine that electric currents in circuits are not flows of electrons, instead they are flows of "charges" or "charged particles." Unless we know what kind of conductor is involved, we cannot know whether an electric current is composed of moving electrons... or whether it's electrons AND positive atoms moving, or whether it's moving positive and negative atoms. For example, if you receive an electric shock, no electrons flowed through your body. Only charged atoms flowed.

This vividly agrees with DaleSpam.

 

[daqddyo1]

We all remember the old TVs with the giant "cathode ray" picture tube. (I even remember and experimented with "vacuum tubes" when I was a kid). In them, electrons streamed from a heated negatively charged electrode and were accelerated by an electric field to paint a picture on the front screen. There was no "back flow" of positive charges in these devices. If there were, the picture producing surface would disappear pretty quickly.

Certainly, one could posit that as a stream of electrons drift through a wire, there could be a series of (+) holes drifting in the other direction. If we did, we would have to be careful not to get trapped by saying for example, that in a wire we have a + current of 2 amps flowing left and a - current of 2 amps flowing right. It is one or the other. I guess this is obvious so why don't we all just call it a day and "go with the flow".

 

[Simon Bridge]

In semi-conductors we talk about "charge carriers" too - there are lots of approximations and shorthands in electrophysics.

Here are certain sites which point out that current flow from positive to negative in reality in DC.

Well if it is on the internet it must be true.

Can you grasp little bit of it ? I find it quite sophisticated. How can charge flow in an electric circuit ? Please tell.

Positive charges flow in the direction of the electric field - negative charges the opposite. What's the problem?

 

[sankalpmittal]

In semi-conductors we talk about "charge carriers" too - there are lots of approximations and shorthands in electrophysics.


Well if it is on the internet it must be true.
Positive charges flow in the direction of the electric field - negative charges the opposite. What's the problem?

I am talking of an electrical DC circuit of metal wires :

1. Which way is current really flowing (i.e. in reality) ?

2. What is current ? Rate of flow of charges (positive charges or negative charges ?) or Rate of flow of electrons ?

3. How are charges really drifting in metal wires circuits ? What actually drifts electrons or charges ?

4. Charge is a property and electrons are subatomic particle , right ? Then how can a property drift ? Are not these electrons ?

5. What is charge really if we talk in this aspect ?

6. Is this analogy correct -: THE CURRENT ALWAYS MOVE FROM NEGATIVE TO POSITIVE.
A 'conventional current flow' does not exist. It is like saying steam is going into the boiling water in the kettle and becomes water. It simply is not so.

7. Are electrons carrying negative charge with them what you call charge flow ? How can positive charge move then ?

_____________________________________________________________________


In the sites I posted the analogy given was that

e[SUP]-[/SUP]     +         e[SUP]-[/SUP]         +    e[SUP]-[/SUP]        +            e[SUP]-[/SUP]            +               e[SUP]-[/SUP]     +        e[SUP]-[/SUP]
------------------------------------------------------------------------------------------------->

---> shows direction of electron. In that site it was given that as electrons drift and change location positive charges develop in metal atoms which is responsible in electric current and not electrons. Is this true ?


Answer these questions and I'll be relieved.
:)

 

[Dale]

Not sure what people mean by charge flow in electric circuits ?
Here are certain sites which point out that current flow from positive to negative in reality in DC. Can you grasp little bit of it ? I find it quite sophisticated. How can charge flow in an electric circuit ? Please tell.

Consider some position in the circuit. Imagine a plane cutting across the wire at that location, and pick a direction (e.g. right) to be positive. Start a clock and every time a + charge goes across to the right or a - charge goes across to the left you will increase a counter, and every time a + charge goes across to the left or a - charge goes across to the right you will decrease the counter. Stop your clock and your count. Multiply your count by the electron charge and divide it by the time on your clock. That is current.

 

[Dale]

1. Which way is current really flowing (i.e. in reality) ?

Current is really flowing in the opposite direction that electrons are drifting.

2. What is current ? Rate of flow of charges (positive charges or negative charges ?) or Rate of flow of electrons ?

See my response to your previous post.

3. How are charges really drifting in metal wires circuits ? What actually drifts electrons or charges ?

Electrons, which are negative charge carriers.

4. Charge is a property and electrons are subatomic particle , right ? Then how can a property drift ? Are not these electrons ?

Because it is carried by the charge carriers (electrons in metal) which drift.

5. What is charge really if we talk in this aspect ?

Charge is a property of fundamental particles which describes their interaction with the electromagnetic force (photons).

6. Is this analogy correct -: THE CURRENT ALWAYS MOVE FROM NEGATIVE TO POSITIVE.
A 'conventional current flow' does not exist. It is like saying steam is going into the boiling water in the kettle and becomes water. It simply is not so.

No. Current goes from positive to negative. Current is defined to go in the opposite direction as electrons or other negatively charged charge carriers.

7. Are electrons carrying negative charge with them what you call charge flow ? How can positive charge move then ?

In metals the positive charge carriers are tightly bound and don't move much (very small thermal motions). However, in other types of materials, such as electrolytes and plasmas, the positive charges are not tightly bound and can also move.

 

[sankalpmittal]

Consider some position in the circuit.

Ok.

Imagine a plane cutting across the wire at that location, and pick a direction (e.g. right) to be positive.

You mean a plane perpendicular to wire at a point ? If so then okay .

Start a clock and every time a + charge goes across to the right or a - charge goes across to the left you will increase a counter, and every time a + charge goes across to the left or a - charge goes across to the right you will decrease the counter.

How are positive charges moving ? [PLAIN]http://www.cci-compeng.com/Unit_2_Electronics/Unit_2_Images/2102_Current.gif

In image the electrons are drifting in a particular direction. Every time the atoms in wire loose electrons from their last orbit , and jump into another atom , they develop positive charge in atom behind them which stays in its position and doesn't move. In image those numbers like 1 , 2, 3 , 4 are the number of positive charges. Electrons move and they develop those positive charges. In fact due to loss of electrons.

I can only understand - what you mean is that if electrons go across the left , i.e. negative charge carriers then there is loss of electrons so I must increase the counter.

Aren't positive charge developed in metal atoms due to loss of electrons are fixed and not moving ? How can they move ?

Stop your clock and your count. Multiply your count by the electron charge and divide it by the time on your clock. That is current.

Ok.

Current is really flowing in the opposite direction that electrons are drifting.

Ok , so is this the discharge or kind of force between positive charges and electrons ?

See my response to your previous post.

You mean that current is the rate of flow of charges.

Electrons, which are negative charge carriers.

Ok.

Because it is carried by the charge carriers (electrons in metal) which drift.

Ok.

Charge is a property of fundamental particles which describes their interaction with the electromagnetic force (photons).

No. Current goes from positive to negative. Current is defined to go in the opposite direction as electrons or other negatively charged charge carriers.

In metals the positive charge carriers are tightly bound and don't move much (very small thermal motions). However, in other types of materials, such as electrolytes and plasmas, the positive charges are not tightly bound and can also move.

Ok.

e-     +         e-         +    e-        +            e-            +               e-     +        e-
------------------------------------------------------------------------------------------------->

---> shows direction of electron. In that site it was given that as electrons drift and leave behind positive charges due to their loss which are developed in metal atoms which is responsible in electric current and not electrons. Is this true ?

Thanks for replying.

:)

 

[Dale]

You mean a plane perpendicular to wire at a point ? If so then okay .

If you are familiar with the vector normal to a plane and the dot product you can extend it to arbitrary shaped surfaces, but a plane is fine.

How are positive charges moving ?

1) I was providing a general definition which would work in the case of positive charge carriers also
2) There is always some thermal motion of the lattice, so on a microscopic scale even in metal you will get positive charges vibrating back and forth across your plane. This thermal motion averages out to 0 and does not contribute to the current, but if you are counting each charge crossing your plane it will have to be considered.

Ok , so is this the discharge or kind of force between positive charges and electrons ?

Current is the movement or flux of charge, it doesn't have units of force.

In that site it was given that as electrons drift and leave behind positive charges due to their loss which are developed in metal atoms which is responsible in electric current and not electrons. Is this true ?

The electrons are the charge carriers in metal. Their drift is responsible for current, and current is defined (see above) in such a way that it points in the direction opposite the drift of the electrons.

 

[sankalpmittal]

If you are familiar with the vector normal to a plane and the dot product you can extend it to arbitrary shaped surfaces, but a plane is fine.

Ok , if that is fine really. :)

1) I was providing a general definition which would work in the case of positive charge carriers also
2) There is always some thermal motion of the lattice, so on a microscopic scale even in metal you will get positive charges vibrating back and forth across your plane. This thermal motion averages out to 0 and does not contribute to the current, but if you are counting each charge crossing your plane it will have to be considered.

Ahh I see !
Now I imagine the real idea of current flow. It is because of the positive charge in metal atoms and electrons or negative charge carriers only contribute to it ! Even that small vibrant motion of positive charged ions is to be considered here.

This means Benjamin Franklin was correct ! Current is the rate of flow of charges and not electrons even in metal wires.

Current is the movement or flux of charge, it doesn't have units of force.

Actually I wanted to mean something else and I typed something else !
Sorry for my grammatical error. I meant that current is the flux which is produced due to back attraction force of electrons and positive charges in metal atoms.

I think I am correct and this is what you mean that current hence flows opposite to flow of electrons in most of cases in metals even.

The electrons are the charge carriers in metal. Their drift is responsible for current, and current is defined (see above) in such a way that it points in the direction opposite the drift of the electrons.

Ok I get it now !

Thank you very much !

 

[Dale]

I meant that current is the flux which is produced due to back attraction force of electrons and positive charges in metal atoms.

Yes, this is basically a re-statement of Ohm's law, which applies in metals as long as they are not superconductive.

Ok I get it now !

Excellent! I am glad to hear it.