Direction of current flow

BR-549

Joined Sep 22, 2013
4,928
studiot.....A plane takes off from NY to London. ~2000 mi.

The NY tower starts counting from 1 to 2000, to monitor the flight.

The London tower starts counting from 2000 to 1 to monitor the flight.

The NY tower uses a positive going magnitude to describe the flight. A
positive flight.

The London tower uses a negative going magnitude to describe the flight. A
negative flight.

It's the same flight.

When the NY tower guy transfers to London.......he had better use the new
reference.........or he will never know where the planes are.

It's just a simple matter of knowing how to PROPERLY change your reference.

But charge flow is a lot more than a plane flight(one way action).

Electricity has symmetry and is always balanced. Two way equal action.

Equal, opposite and balanced. Two equal exchanges or transfers.

This means two charge flows.
 

MikeML

Joined Oct 2, 2009
5,444
I agree with ernie's question.

For a cathode ray, I would not say that a current of any description flows from the screen to the cathode, ...
I would, especially if I was designing the HV power supply to run the CRT.

I would say that electrons boil off the cathode, and are formed into a beam, and accelerated toward toward the phosphor by the anode. It takes a positive high voltage from cathode to anode to attract the negatively-charged electrons, and create the beam of electrons.

Current flows from the positive terminal of the HV power supply toward the anode. The negative terminal of the power supply is connected to the cathode. Current flows from the cathode toward the negative terminal of the HV power supply.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
I agree with ernie's question.

For a cathode ray, I would not say that a current of any description flows from the screen to the cathode, any more than I would say a negative aircraft flying from london to New York is the same as a positive aircraft flying from New York to London.
I agree.
As in a TV CRT the voltage is accelerated by the +ve H.V. on the CRT internal aquadag coating and propelled/accelerated toward the screen, the beam after being focused is deflected by the vert/horiz scan coils..
Max.
 

crutschow

Joined Mar 14, 2008
34,285
Where exactly is the phosphor connected into the circuit?
The high-voltage anode connection on the CRT tube neck goes to the phosphor coating, which has sufficient conductivity to become charged to the anode voltage.
If you place the back of your hand on the front of a CRT when it is turned on, you can usually feel the hairs on the back of you hand being attracted by the high voltage field from the charged phosphor.
 

MaxHeadRoom

Joined Jul 18, 2013
28,619
It it has always been my understanding that the anode is the +coating (aquadag) on the inside of the tube at the anode HV anode connection.
This is what accelerates the electron steam which eventually ends up on the phosphor, the neck contains the 'guns', 3 in the case of colour.
The stream has to pass through the dots in the shadow mask immediately behind the phosphor coating in the front of the CRT in order to strike the phosphor.
(The shadow mask gets demagnetized be external means every time the set is switch on).

Max.
 

cmartinez

Joined Jan 17, 2007
8,220
It it has always been my understanding that the anode is the +coating (aquadag) on the inside of the tube at the anode HV anode connection.
This is what accelerates the electron steam which eventually ends up on the phosphor, the neck contains the 'guns', 3 in the case of colour.
The stream has to pass through the dots in the shadow mask immediately behind the phosphor coating in the front of the CRT in order to strike the phosphor.
(The shadow mask gets demagnetized be external means every time the set is switch on).

Max.
Ahhhh... in this day and age of LCDs, IPS's, LEDs, Plasma, OLEDs and electronic paper... seeing a CRT blowout view like that makes me feel young again...
 
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WBahn

Joined Mar 31, 2012
29,979
I agree with ernie's question.

For a cathode ray, I would not say that a current of any description flows from the screen to the cathode, any more than I would say a negative aircraft flying from london to New York is the same as a positive aircraft flying from New York to London.
Then what would you say? That a current of one ampere flows from the cathode to the screen?

We don't have positive aircraft and negative aircraft, so using those as intuitive examples is anything by intuitive.

We do have things like transactions into financial accounts that are both positive and negative so that makes a much better example and negative money being deposited into an account is exactly the same as positive money being drawn out of it. Plenty of transactions are listed exactly this way on numerous financial statements. I just got my statement from our utility provider and ALL transactions are referred to positive amounts adding to the balance due, so payments are listed as negative additions to the balance.
 

WBahn

Joined Mar 31, 2012
29,979
I agree.
As in a TV CRT the voltage is accelerated by the +ve H.V. on the CRT internal aquadag coating and propelled/accelerated toward the screen, the beam after being focused is deflected by the vert/horiz scan coils..
Max.
What does it mean for the "voltage to be accelerated"?

If you want to say that electrons flow from the cathode to the screen, then fine. That's an accurate description. But current is the flow of charge, not the flow of charge carriers. As soon as you start talking about what the current is or start expressing things in coulombs or amperes, then you either have a negative current flowing from the cathode to the screen or you have a positive current flowing from the screen to the cathode -- both are accurate statements. What you do NOT have is a positive current flowing from the cathode to the screen.
 

tjohnson

Joined Dec 23, 2014
611
Blame Ben Franklin.:D I heard that the idea of current flowing in the positive direction originated with him. He was a great scientist, though.
 

WBahn

Joined Mar 31, 2012
29,979
Blame Ben Franklin.:D I heard that the idea of current flowing in the positive direction originated with him. He was a great scientist, though.
It wouldn't have made a difference whatever Ben had picked -- positive current would still flow from positive voltage to negative voltage in a device consuming electrical energy because that is a consequence of the very definition of voltage, which is the work needed to move a positive test charge at constant velocity within an electric field and the electric field is defined in terms of the force exerted on a positive test charge at a given location. The passive sign convention would be completely unaffected. If Ben had made his choice such that the electron ended up being labeled as having a positive charge, nothing would have changed mathematically. The effect would have been that batteries would have their terminals labeled the other way. We would likely have positive ground in most automobiles because that is not arbitrary, but rather a result of electrochemical effects on corrosion behavior. The cathode in a TV would be at a high positive voltage instead of a high negative voltage. What we call p-type and n-type semiconductors would have the names reversed -- and students and others would still get endlessly confused about "hole flow" except now it would be called "negative hole flow" instead of "positive hole flow".
 

wayneh

Joined Sep 9, 2010
17,496
I'm thinking current flow should become a banned topic here. Surely we've wasted more time on it than we ever have on free energy. :p

No offense to any of the panelists - a rigorous discussion and understanding of something we take for granted can be fruitful. But an arbitrary convention? o_O
 

studiot

Joined Nov 9, 2007
4,998
We don't have positive aircraft and negative aircraft, so using those as intuitive examples is anything by intuitive.
Exactly so.

And we don't have a choice of positive or negative cathode rays.

So I repeat, where exactly is the phosphor connected into the circuit? As I understand it phosphors are not conductive and do not form an intentional part of the circuit. The negative only cathode rays are accelerated towards and through the anode to strike the non conductive phosphor and release the light. Electrons are drained off via the (aluminium) conductive layer.

From Wiki
The phosphors are usually poor electrical conductors. This may lead to deposition of residual charge on the screen, effectively decreasing the energy of the impacting electrons due to electrostatic repulsion (an effect known as "sticking"). To eliminate this, a thin layer of aluminium is deposited over the phosphors and connected to the conductive layer inside the tube. This layer also reflects the phosphor light to the desired direction, and protects the phosphor from ion bombardment resulting from an imperfect vacuum[/quote}
 

MrChips

Joined Oct 2, 2009
30,720
Whoever said that the electron was negatively charged to begin with?
Why isn't the electron positively charged?

I think this goes way back to electrochemical cells when early scientists were playing around with voltaic cells long before they even conjured up electrons.

All they knew was that when two dissimilar metals were placed in an electrolyte they were able to produce an electric current, some stronger than others.

So they set about to list metals in the order of their electrochemical potential. Gold and copper ended up on one end of the table and iron and lead on the other end.

Now depending on how they arranged the list, one metal was considered more positive than the other. If they had flipped the table we would have ended up with positive electrons and we would not be arguing over this.

So don't blame it on Benji.
 

WBahn

Joined Mar 31, 2012
29,979
What does it matter whether the phosphors are conductive or not (for this discussion)? Why are you stuck on that? The electrons that impact the phosphor screen MUST be part of a complete circuit. The details of HOW they are drained off is irrelevant (unless you are building a phosphor screen). The fact that phosphors are poor conductors just means that some other means of creating a conductive layer is needed because the electrons MUST be drained off and returned to the circuit. If they aren't, then the screen would build up a negative charge which would repel the electron beam and this would happen very quickly. So they are collected by a thin layer of aluminum. So what? They are then returned to the circuit that originally supplied them to the gun (of course, not necessarily the same exact electrons but a one-for-one exchange -- one electron leaves the HV supply and travels to the gun, one electron leaves the gun, one electron impacts the phosphor screen, one electron enters the aluminum layer, one electron leaves the aluminum layer back into the circuitry, one electron moves from the circuitry into the HV supply.

You are still evading the question.

If you want to define the current in the direction of the motion of the electrons, fine. I will ask again and more explicitly. If 6.24x10^14 electrons are fired from the CRT gun toward the phosphor screen, and if electrical current is chosen such that positive current flows from gun to screen (i.e., if we use "electron current"), what is the e-beam current expressed in microamps?
 

Thread Starter

Yakima

Joined Jan 23, 2012
35
studiot.....A plane takes off from NY to London. ~2000 mi.

The NY tower starts counting from 1 to 2000, to monitor the flight.

The London tower starts counting from 2000 to 1 to monitor the flight.

The NY tower uses a positive going magnitude to describe the flight. A
positive flight.

The London tower uses a negative going magnitude to describe the flight. A
negative flight.

It's the same flight.

When the NY tower guy transfers to London.......he had better use the new
reference.........or he will never know where the planes are.

It's just a simple matter of knowing how to PROPERLY change your reference.

But charge flow is a lot more than a plane flight(one way action).

Electricity has symmetry and is always balanced. Two way equal action.

Equal, opposite and balanced. Two equal exchanges or transfers.

This means two charge flows.
This reminds me of an incident I read of in one of Winston Churchill's books -- I forget which one -- where he related a confusion between the American staff and the British staff over a phrase. The Americans were wanting to invade a region -- I forget which -- in concert with the British. Radio communications said that plan was "off the table," which to Americans meant abandoned, but to British meant it was what the Americans thought of as "on the table," and being worked on by staff. Fortunately, they got it sorted out.

P.S. Upon reflection I think I got it mixed up: The British use the term "on the table" to mean its being examined, while the Americans use the term "off the table" to mean the same thing. I'
m getting old.
 
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killivolt

Joined Jan 10, 2010
835
I guess mentioning a "Vacuum Capacitor" now; is off the table. lol

Just kidding; I alway enjoy these "Threads" and the different clever ways the real world gets dragged into the explanations.

Really liked the planes and - and + bank statements. It does help people get a clue in on the small world of the humble worker "bee" the electron.

Hey, can you do one on a beehive for me?:rolleyes:
 

Thread Starter

Yakima

Joined Jan 23, 2012
35
I guess mentioning a "Vacuum Capacitor" now; is off the table. lol

Just kidding; I alway enjoy these "Threads" and the different clever ways the real world gets dragged into the explanations.

Really liked the planes and - and + bank statements. It does help people get a clue in on the small world of the humble worker "bee" the electron.

Hey, can you do one on a beehive for me?:rolleyes:

I'll stir up the hornet's nest with my next thread "Is the 120/240 volt electrical system in the US single phase or two phase?"
 

WBahn

Joined Mar 31, 2012
29,979
I think of it as single phase (or split single phase), but I think an argument can be made that describing it as two-phase is not inaccurate, either. It comes down to semantics. Historically the name two-phase was used for two voltage waveforms in quadrature. But that's really just a particular instantiation of a system with two phases and is not the definition of the term "two phase". In most polyphase systems, lacking anything to the contrary, the phases are equally spaced in phase, so a 2-phase system would reasonable be two phases 180 degrees out and, arguably, the what was known as two-phase should have had a qualifier such as "2-phase quadrature", but since it was the only two phase system at the time (I believe) there was no need to distinguish it from anything else. Just as you "could" have a three-phase system in which the phases were, for some strange reason, 0°, 26°, and -17.2°.
 
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