Electron free transistors.

[Bob_the_lost]

But you can also have mols of ions. So mols aren't restricted to atoms.

That's like saying you can do a headcount when you're trying to count the number of prosthetic limbs you've got in stock. Meaningless.

A mol isnt' just a random number picked for fun it's the number needed to convert between Atomic weight and grams. Since i'm in the mood for stupid analogies tonight it'd be like measuring the speed of light in units of jamjars.

You're still using chemisty documents, where free electrons or the outer shell's electrons are the variable, very different to electrical terms. Go dig up a physics or electronics text on the topic.

 

[gnoriac]

But you can also have mols of ions. So mols aren't restricted to atoms.

Ions are just atoms stripped of outer electrons, ain't they?

 

[WouldBe]

You're still using chemisty documents, where free electrons or the outer shell's electrons are the variable, very different to electrical terms. Go dig up a physics or electronics text on the topic.

Except Faradays law links mols of any substance liberated in electrolysis with coulombs which can be expressed in Amps per second so there is a link between mols and A/s and therefore a link between number of electrons and A/s.

 

[WouldBe]

I = nAVQ.

Current= Number of charge carriers * Crossectional area of conductor * drift velocity * Charge per unit carrier.

I/AVQ = n

Drift velocity is only around .1mm a second, give or take, assume a wire of a few mm thick...

Is this where the problem lies. http://www.iop.org/Our_Activities/Schools_and_Colleges/Teaching_Resources/Teaching%20Advanced%20Physics/Electricity/Electric%20Current/page_2999.html

You can't just work out the drift velocity from a blob of KMNO4 on damp filter paper. In electophoresis the distance ions travel when exposed to an electrical current is dependant on the size of the ion, the charge on the ion and the resistance caused by the interaction of the ions with the medium it is travelling through which is why when you do electrophoresis on a DNA sample (for example) you get a whole range of visible marks depending on how mobile the DNA fragments are.



E2A: If you look at that link you will note that mols play apart in your calculation.

 

[Knotted]

I'm not clear on how semiconductors work but surely its not the actual electrons which change the state of the semiconductor but the electrical field induced by the electrons. So its not a question of shovelling in electrons like you might shovel coal into a furnace.

Even with such a microscopic (or picoscopic!) current that no new electrons are pushed into the capacitor (most of the time) there will still be a correspondingly tiny field energy to set off the correspondingly sensitive transitor.

But anyway that's just me half remembering my A level physics.

 

[WouldBe]

But with effectively no electrons there is no electric field either.

 

[Knotted]

But with effectively no electrons there is no electric field either.

But presumably there is still a miniscule movement of electrons in the wire leading to the transistor and even if this movement is too small to actually shovel any electrons in, it would still create an eletrical field which could still produce the desired effect in the transistor.

 

[WouldBe]

Wrt I=nAVQ

From my link you get this example

Consider a current of 1 A in a copper wire of cross-sectional area 1 mm2.

Assume one free electron per atom. (This is a good estimate.) So we need to find the number of atoms present.

For copper (density 8900 kg m-3 and atomic mass no. 63.5):

In 1 m^3 there are 8900/0.0635 moles of Cu atoms = 8.4 x 10^28 atoms / m^3

This gives a value of n of order 10^29 m^-3

Rearrange the equation to give: v = I/nAq and substitute values to get;
v = 1/(10^29 x 1 x 10^-6 x 1.6 x 10^-19) = 6 x 10^-5 m s^-1

If you now increase the current to 10A this would give a drift velocity of 6 x 10^-4 m s^-1 = 0.6mm per second

This is the only thing that can change as there are still the same number of charge carriers in the same diameter of wire and the charge on an electron is a constant.

 

[Knotted]

This is the only thing that can change as there are still the same number of charge carriers in the same diameter of wire and the charge on an electron is a constant.

But just because there is still the same number of electrons in a particular section of wire (its presumably three dimensional not two) it does not mean that there has not been a shift of electrons within that section of wire. All its saying is that the motion was insufficient to produce an input and an output to that particular section. If we take a subsection or a supersection or a completely different section that might not be the case. Surely the current in a circuit is the average rate of flow of electrons and surely the only measureble effect is the electrical field not the actual positions of the electrons (which is subject to quantum uncertainty anyway).

 

[WouldBe]

surely the only measureble effect is the electrical field not the actual positions of the electrons (which is subject to quantum uncertainty anyway).

Don't electric fields only have an effect in Field Effect Transistors (FET's) whereas in NPN transistors it relies on a current (moving electrons) into the base of the transistor.

 

[Knotted]

Don't electric fields only have an effect in Field Effect Transistors (FET's) whereas in NPN transistors it relies on a current (moving electrons) into the base of the transistor.

I really don't know, but with my limited knowledge I would have thought the only effect an electron could have on its environment is through the electro-magnetic field it generates. Surely the strong and weak nuclear forces are not coming into play here.

Besides the transitor will have electrons of its own to create a current which would presumably be induced by an electrical field.

 

[WouldBe]

Besides the transitor will have electrons of its own to create a current which would presumably be induced by an electrical field.

But with an NPN type transistor unless there are electrons moving into the base region the transistor is off and no current is flowing in the transistor either.

 

[Bob_the_lost]

Except Faradays law links mols of any substance liberated in electrolysis with coulombs which can be expressed in Amps per second so there is a link between mols and A/s and therefore a link between number of electrons and A/s.

No.

Electrons are not a substance. You can't liberate them using electrolysis. Stop trying to use chemistry to understand physics, it does not compute.

 

[WouldBe]

No.

Electrons are not a substance. You can't liberate them using electrolysis. Stop trying to use chemistry to understand physics, it does not compute.

Of course it does.

Sodium is produced by electrolysing molten soduim chloride.

For every Na+ that is liberated as Na 1 electron has to be put in. So to liberate 23g of sodium you need to put 6.02 x 10^23 electrons through the circuit.

Therefore you can count the electrons used in the process.

 

[Bob_the_lost]

Of course it does.

Sodium is produced by electrolysing molten soduim chloride.

For every Na+ that is liberated as Na 1 electron has to be put in. So to liberate 23g of sodium you need to put 6.02 x 10^23 electrons through the circuit.

Therefore you can count the electrons used in the process.

That's nice dear.

Stop trying to use chemistry to understand physics.

 

[Knotted]

But with an NPN type transistor unless there are electrons moving into the base region the transistor is off and no current is flowing in the transistor either.

It seems that the model breaks down at these extremes. I would have thought the usual model of electrons flowing in and out of elctrical circuits is a macroscopic approximation. I wouldn't have thought that charge is conserved microscopically for example - surely there is the odd free electron and the odd free ion hanging about in any given material. But at the end of the day the only effect is to do with electrical fields. In this extreme example I would think that its best to couch the question in these terms rather than the flow of electrons.

 

[WouldBe]

That's nice dear.

Stop trying to use chemistry to understand physics.

I think you will find the 2 subjects are highly interlinked. Without knowing chemistry you wouldn't have electrics and electronics.

 

[Knotted]

Wikipedia has this to say about bipolar junction transistors (of which NPN transistors are an example of):

"Small changes in the voltage applied across the base–emitter terminals causes the current that flows between the emitter and the collector to change significantly. This effect can be used to amplify the input voltage or current. BJTs can be thought of as voltage-controlled current sources, but are more simply characterized as current-controlled current sources, or current amplifiers, due to the low impedance at the base."
http://en.wikipedia.org/wiki/Bipolar_junction_transistor

So I think I might be correct in saying that the usual description is technically incorrect. Its the electrical pressure difference (voltage) that switches the transistor and the current is actually just an implicit consequence of this voltage. Maybe?

 

[Bob_the_lost]

I think you'll find that trying to analyse processes that function on the QM level using crude tools like those used in chemisty will lead you to nonsensical results.

As seen above.

 

[WouldBe]

I think you'll find that trying to analyse processes that function on the QM level using crude tools like those used in chemisty will lead you to nonsensical results.

As seen above.

Which was why I posed the question cos it didn't make any sense.

So what's the answer?

 

[Bob_the_lost]

That it's complicated.

No one works in those numbers. You'd need to know the Doping levels for both the P region and N regions, as well as a few other factors that you can dig up with a bit of work.