How does charge transfer relate to electromagnetic radiation?

[vitality00]

Charge transfer = electrons flowing from positive to negative

Electromagnetic radiation = electric + magnetic field

[swansont]

If you accelerate a charge, you will get electromagnetic radiation.

[Nicholas Kang]

No, electrons flow from negative terminal (of a battery/cell) to the positive terminal. The charge transfer that you mentioned is known as the conventional current flow. Such confusing versions exist because the discovery of electricity is much earlier than the discovery of electrons.

 

For electromagnetic radiation, it is the magnetic field feeds an electric field and vice versa. One magnetic field exists and then disappeared before another electric field emerge. This occurs at 90 degrees in relative to each other. Usually, you can see reference books showing that the magnetic field is upright and the electric field is 90 degrees tilted to its side after the magnetic field disappears.

 

And for swansont`s explanation, you must be aware that acceleration does not mean only a change in speed but also change in direction. This means you can change the direction of an electron to kick start an electromagnetic field instead of increasing its speed though both are possible, iirc.

 

Nicholas

If you accelerate a charge, you will get electromagnetic radiation.

 

Positive or negative charge? Or both are possible?

Edited September 10, 2014 by Nicholas Kang

[swansont]

 

Positive or negative charge? Or both are possible?

 

Any charge. But electrons tend to accelerate more easily than any other charged particle, because of their small mass.

[Nicholas Kang]

Well swansont, I shall learn from you now. The charge here doesn`t only mean positive and negative? Can you list out some examples of charges apart from the +ves and -ves? Is Red, Green, Blue of nucleons considered as a charge under quantum chromodynamics?

Edited September 10, 2014 by Nicholas Kang

[swansont]

Well swansont, I shall learn from you now. The charge here doesn`t only mean positive and negative? Can you list out some examples of charges apart from the +ves and -ves? Is Red, Green, Blue of nucleons considered as a charge under quantum chromodynamics?

 

By any charge I mean positive or negative. Electron, positron, proton, muon, etc.

[studiot]

 

No, electrons flow from negative terminal (of a battery/cell) to the positive terminal. The charge transfer that you mentioned is known as the conventional current flow. Such confusing versions exist because the discovery of electricity is much earlier than the discovery of electrons

 

Do they?

 

In an incomplete external circuit they don't 'flow' at all, despite the electric field that exists between the terminals.

 

In a complete external circuit the do indeed 'flow' from what we call the negative terminal to the positive terminal.

 

But

 

Within the battery they must flow the other way to complete the circuit.

[Nicholas Kang]

 

By any charge I mean positive or negative. Electron, positron, proton, muon, etc.

I get what you mean. You mean charges as in the standard model of elementary particles.

 

Do they?

 

In an incomplete external circuit they don't 'flow' at all, despite the electric field that exists between the terminals.

 

In a complete external circuit the do indeed 'flow' from what we call the negative terminal to the positive terminal.

 

But

 

Within the battery they must flow the other way to complete the circuit.

 

I understand you first and second statement regarding "incomplete and complete" external question. But I don`t understand what do you mean by the other way in the second statement. Can you clarify it? And what is external circuit, what is its opposite? Internal circuits?

[studiot]

Take a battery and a simple connected circuit.

 

Which way does conventional current flow?

 

Well it won't flow at all unless there is a complete closed path all the way round from terminal A of the battery through all the connected wires and components to terminal B of the battery and back through the battery to terminal A.

 

All the connected stuff is called the external circuit, from A round to B.

 

The part back through the battery is called the circuit within the battery.

 

It takes both parts to make a complete circuit or loop or closed path.

 

Usually the external circuit is much larger than the battery so we often refer just to this part as 'the circuit'.

 

However consider a technicain testing a large lorry battery with an automotive battery discharge tester.

 

The battery is very large compared to the size of the discharge tester, so which is 'the circuit' now?

 

 

 

[Nicholas Kang]

The current flow in battery of course in conventional flow diagram is from negative to positive to complete the external circuit. If conventional current flows from positive to negative within the battery, the whole circuit simply fails. I understand that. In my Form 3 syllabus, and in most condition, I(we) won`t take the current flowing within the cell into account/consideration. But you want(or maybe always) to be specific, so sorry for misunderstanding your meaning. It is always good to be precise in science because it is easier for clarifications to be done.

 

But for electron flow, it must be the other way round. You must agree with me, mustn`t you?

 

For your question, I can get the rough meaning you advise me to be more specific and look through all possible conditions in detail. So, "the circuit"-"the external circuit" that is normally referred to as the external circuit of the simple circuit is now the battery, the whole battery which in correct way of saying it should be the circuit within the cell whereas the external circuit is the discharge tester, am I correct?

[studiot]

Yes of course electron flow is in the opposite direction to conventional current.

 

I do not want to get into an electron flow v conventional argument.

 

What I am saying is like imatfaal's model elsewhere.

 

We choose a direction and set up our models (mathematical equations) to suit.

 

The electron flow model is actually unhelpful (IMHO) to most leaning circuit theory and leads to the difficulties I outlined.

 

Remember circuit theory is a mathematical model designed to facilitate the calculation of componeent values for design and analysis purposes.

It is not intended to offer a model of the physics of electricity.

 

Treated as a design and analysis tool is works well.

[Nicholas Kang]

Ok, you basically solve one of my questions-why use conventional flow diagram instead of electron flow when the latter is proven correct. Yet, books like Understanding Physics by Robin Millar, University of York, New York, published in the 1990s use the electron diagram instead of the conventional`s. Can I ask you would the calculations of the circuit theory in conventional form affects the results of electron flow calculation in reality/real world calculations?

[studiot]

 

Ok, you basically solve one of my questions-why use conventional flow diagram instead of electron flow when the latter is proven correct. Yet, books like Understanding Physics by Robin Millar, University of York, New York, published in the 1990s use the electron diagram instead of the conventional`s. Can I ask you would the calculations of the circuit theory in conventional form affects the results of electron flow calculation in reality/real world calculations?

 

There are two separate issues.

 

Firstly not all current flow is by electrons, or even negatively charged carriers. Sometimes carriers of both polarity are involved.

 

So whichever is chosen will be 'wrong' for the other.

 

Moreover carriers can be massive ions or small particles like electrons and 'holes'.

 

In fact most theories do not require electrons, just 'carriers' which often need not be described further.

 

Secondly all the equations in elctrodynamics and electrostatics are set up using the direction of conventional current.

Many are vector equations which contain inherent directional information.

All of these would be incorrect if we changed direction of current in conductors.

 

So a direction was chosen a couple of centuries ago and we apply a plus or minus sign to any equation if the polarity of the charge affects it.

 

That strategy resolves all known problems.

 

Nevertheless there was a move in the 1990s to promote the reversal of the standard direction to make the direction of negative carriers positve (?!!??).

 

That has caused much confusion as you note and is falling out of fashion.

 

I would avoid it as far as possible.

[Sensei]

More informations about electromagnetic radiation:

http://en.wikipedia.org/wiki/Bremsstrahlung

http://en.wikipedia.org/wiki/Synchrotron_radiation

http://en.wikipedia.org/wiki/Cyclotron_radiation

 

 

 

So a direction was chosen a couple of centuries ago ... (...)

 

Studiot, but centuries ago they picked up wrong direction of current I..

 

You see arrow of I is going from + to - in battery, while electrons are flowing in exactly opposite direction:

[studiot]

 

Studiot, but centuries ago they picked up wrong direction of current I..

 

Did they?

 

So what is the correct direction of current if I replace your battery with the AC mains?

I would see the same (heating) effect in the external resistor.

And are there not actually more AC circuits than DC ones in this world?

And that still did not answer the question what is the direction from + to - within the circle you have drawn?

 

The whole point is that most theory is independent of the direction of carrier flow.

If this become necessary it is simply covered by assigning the same sign as that of the charge to the flow.

Surely you cannot be suggesting that electrons simply move around your path through the resistor from - to plus and stay there at the + sign, building up an excess of negative charge, which would repel further electrons arriving?

Edited September 10, 2014 by studiot

[Sensei]

So what is the correct direction of current if I replace your battery with the AC mains?

AC is swapping direction of electrons 50 Hz or 60 Hz, times per second, depending on country.

So for AC both answers are correct.

 

I would see the same (heating) effect in the external resistor.

Correct.

This can be even experimentally confirmed by plugging heating element to AC, and heating water (with mass m, and initial temperature T₀), then through rectifying diodes DC (and heating it for the same period of time, same mass, same initial temperature).

 

~4.1855 J/K*g

m=250 g of H₂O

T₀=20 C

T₁=100 C

~4.1855 * ( 100 - 20 ) * 250 = 83710 J

For U = 230 V, I = 2 A, time needed to increase temperature of water from 20 C to 100 C will be approximately 83710 / 460 = 182 seconds = 3 minutes 2 seconds..

 

And are there not actually more AC circuits than DC ones in this world?

But it's meaningless which one is more or less used. AC is used to transfer energy on large distances, while DC is what we use in f.e. electronic equipment. There is just a few devices that doesn't need DC, like light bulb, or heating element, that works regardless of direction of electrons/current. But diodes and transistors bother about it. LED won't shine light after plugging it reverse.

You won't make electromagnet with AC for instance. It needs DC. Constant flow of electrons in one direction.

Electromagnet that will be changing direction 50/60 times per second will not work.

 

Whether electromagnet is repelling or attracting magnets is quite substantial difference...

 

I can show you in couple minutes on video recorded by my phone how direction of current through my electromagnet is causing on compass array below it..

 

Electric motor will be spinning in opposite direction after applying to it current with opposite direction.

 

And that still did not answer the question what is the direction from + to - within the circle you have drawn?

 

The whole point is that most theory is independent of the direction of carrier flow.

If this become necessary it is simply covered by assigning the same sign as that of the charge to the flow.

 

Did you see my experiments with Cockcroft-Walton generator with 40000+ volts videos?

 

Electrons gather on one side of capacitors, while other side has excess of electrons.

 

We will see how on positive electrode will appear coronal discharge. Sometimes it looks like little violet thunderbolts. Positive electrode is stealing electrons of air medium, and medium is stealing electrons from surrounding it medium and it's going and going, like thunderbolt, with time. It takes even a few seconds when we can observe it growing. Once it reaches negative electrode, there is appearing electric arc between them, and electrons gathered on capacitors will flow freely to positive electrode, discharging. And then it can start from beginning.

 

Just by looking at electrodes I can tell you which has excess of electrons, and which one has abundance of them. It's clearly visible after a few seconds while capacitors are loading..

Negative electrode (that has abundance of electrons) cannot steal electrons from Nitrogen & Oxygen from air, it has too many of them.

Coronal discharges differ (visible by naked eye) between positive & negative electrodes.

 

 

 

Surely you cannot be suggesting that electrons simply move around your path through the resistor from - to plus and stay there at the + sign, building up an excess of negative charge, which would repel further electrons arriving?

Of course they stop flowing, when there is no more abundance electrons, and no more "holes".

 

The same is with charged capacitor. Electrons can flow from - side of it, to +, only to moment of ~full discharge...

 

And that still did not answer the question what is the direction from + to - within the circle you have drawn?

 

Actually I didn't draw it. These are images from wikipedia.

Edited September 11, 2014 by Sensei