A science question

[sonicbomb]

One for the science minded geeks that I know patrol these shores.

Why doesn't the thermionic effect short circuit a domestic light bulb?

Electrons produced by the filament should be drawn directly to its positive terminal. Why doesn't this current flow draw power away from the anode or short circuit the filament completely?

The thermionic effect was rediscovered by Edision in 1880 while investigating filament breakage and anode darkening in his incandescent bulbs. He promptly patented it.
Thermionic emission - Wikipedia

A modern tungsten filament is definitely boiling off electrons as it's work function is well below the 2500 centigrade that modern filaments run at. Modern light bulbs do not seem to suffer from this effect, but Edison's did.

Is it that the anode/cathode potential is too low in a modern light bulb compared to Edision's to produce the a sufficient current flow to significant? I've tried googling the hell out of this, and despite increasing my knowledge of the associated technology I can't find an answer.

 

[CMD-Ky]

@Bunnykiller

 

[DaveP]

My first guess is that the filament is at the same potential from the supporting wire, through the incandescent coil and back down the wire on the other side. Yes, there would be difference of potential between the two sides of the supporting wire, but all along the entire circuit the voltage is the same except for polarity in the two sides in a DC confirguration.

Edison encountered problems with power transmission more than a mile using direct current and finally discovered that he could achieve longer electrical transmission over lines more than a mile by using alternating current.

 

[stols001]

Per the Autistic husband:

The amount of force it takes to push/draw the current through the material is what matters. The material causes friction which is the impetus for the splitting off of the electrons.. You lower the amplitude (a smaller wavelength) and you you have less friction because amplitude is a wave form and it passes through less material or space/time at a higher amplitude or straight line. thus in order to acquire a lower amplitude you change the material you are passing the electric current through. I.e. Halogen light bulbs, LED light bulbs, Neon lightbulbs, florescent tubes all contain gas instead of Tungsten except for the LED which is a crystal container.

Furthermore, improving the container that all of this action/reaction happens within eliminates contaminants that also cause friction. Keep in mind, that all the action/reaction happens at the center between the two polarities. Thus, again, allowing a lower amplitude to create the reaction/action.

Synopsis: Bigger is not always better, faster is not always quicker, and brighter is not always fancier, either. There may actually be less stuff involved.
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Brought to you by Autistic Husband who knows everything.

I got nothing. I wanted to see if he did. Do let me know if it's correct @sonicbomb

 

[sonicbomb]

My first guess is that the filament is at the same potential from the supporting wire, through the incandescent coil and back down the wire on the other side. Yes, there would be difference of potential between the two sides of the supporting wire, but all along the entire circuit the voltage is the same except for polarity in the two sides.

"The effect was rediscovered again by Thomas Edison on February 13, 1880, while he was trying to discover the reason for breakage of lamp filaments and uneven blackening (darkest near the positive terminal of the filament) of the bulbs in his incandescent lamps."

Then what has changed either intentionally or not that a modern light bulb does not exhibit the same behaviour as Edisons?
I agree that what you describe is a significant factor. However I suspect the answer to my question is that modern light bulbs are filled with low pressure inert gases like argon or nitrogen. I still need to read up on the history of light bulbs, but I'm pretty sure that for a long time domestic bulbs used a vacuum. Why were they not affected?

Incandescent light bulb - Wikipedia

Per the Autistic husband:

I was a bit bemused by your reference to your husband as autistic. I'm guessing that this is an 'in-joke' that you guys share and that he isn't actually autistic. Help me to understand please.

I found it a little hard to follow what he was saying. But in essence I think he is agreeing with DaveP in terms of the filament being the path of least resistance. If so, it still doesn't explain why modern bulbs don't and at least Edisons bulb did. If you read that section on wikipedia it was a significant effect that was actually damaging the bulbs, and one that led to the vacuum tube (valve), the cathode ray tube used in televisions and x-ray tubes.

 

[DaveP]

"The effect was rediscovered again by Thomas Edison on February 13, 1880, while he was trying to discover the reason for breakage of lamp filaments and uneven blackening (darkest near the positive terminal of the filament) of the bulbs in his incandescent lamps."

Then what has changed either intentionally or not that a modern light bulb does not exhibit the same behaviour as Edisons?
I agree that what you describe is a significant factor. However I suspect the answer to my question is that modern light bulbs are filled with low pressure inert gases like argon or nitrogen. I still need to read up on the history of light bulbs, but I'm pretty sure that for a long time domestic bulbs used a vacuum. Why were they not affected?

Incandescent light bulb - Wikipedia

Achieving a proper vacuum was Edison's folly as he experimented with design. I seem to remember that he used several filament materials (carbonized Bamboo was one?) and finally got the lamp to survive without destroying the filament.

Who Invented the Light Bulb? | Live Science

The patent listed several materials that might be used for the filament, including cotton, linen and wood. Edison spent the next year finding the perfect filament for his new bulb, testing more than 6,000 plants to determine which material would burn the longest.
Who Invented the Light Bulb? | Live Science

 

[stols001]

Nah, he's not autistic at all. He just knows a bunch. But to many women ALL men have a slight tinge of like autism. I call him that for time Keep in mind I am super emotional.

Anna

 

[DaveP]

The filament is actually the highest resistance component in the chain. Higher resistance is what creates a voltage drop across the filament and that results in more heat across those two points as current slows down due to resistance in its path (electrons back up and begin to crowd into a small area where luminescence can occur).

To answer the original question, the filament doesn't burn up because it's encased in a bulb that is infused with a gas that doesn't support combustion as room air containing oxygen would. It also has a resistance high enough to slow electron flow and create light and heat without causing destruction of the filament wire or the supporting components.

LED's do this more efficiently than resistive metallic filaments at high voltage.

 

[sonicbomb]

@DaveP
Understood. The question is why do we not see issues caused by the thermionic effect in modern light bulbs.

 

[Bunnykiller]

One for the science minded geeks that I know patrol these shores.

Why doesn't the thermionic effect short circuit a domestic light bulb?

Electrons produced by the filament should be drawn directly to its positive terminal. Why doesn't this current flow draw power away from the anode or short circuit the filament completely?

The thermionic effect was rediscovered by Edision in 1880 while investigating filament breakage and anode darkening in his incandescent bulbs. He promptly patented it.
Thermionic emission - Wikipedia

A modern tungsten filament is definitely boiling off electrons as it's work function is well below the 2500 centigrade that modern filaments run at. Modern light bulbs do not seem to suffer from this effect, but Edison's did.

Is it that the anode/cathode potential is too low in a modern light bulb compared to Edision's to produce the a sufficient current flow to significant? I've tried googling the hell out of this, and despite increasing my knowledge of the associated technology I can't find an answer.

first off, the bulb is filled with an inert gas ( krypton, argon) or is under a vacuum, both of which are reluctant to produce an arc to allow enuf current to flow at the voltages supplied, but if you raise the voltage above 1500V, an arc will very easily appear, and the filament is taking most of the current anyway. Ever notice a quick flash just as a bulb burns out? that is the arc that occurs that the question is all about. That arc occurs and uses up the available materials in the vacuum and deposits them on the anode. Once that happens and the supply is depleted and the arc dies out nothing else occurs.

Thermonic effect is predominate in vacuum tubes for old TVs and Radios ( diode triode tubes) and, thermonic effect works better with a DC voltage as seen in hi power tube type gas lasers.

and finally, the tungsten used today is purer than Edisons supply, his supplies had so much contaminates in it, it would produce enuf crud to be an issue.

 

[Letitia]

The things you learn on ecf eh?

 

[Bunnykiller]

My first guess is that the filament is at the same potential from the supporting wire, through the incandescent coil and back down the wire on the other side. Yes, there would be difference of potential between the two sides of the supporting wire, but all along the entire circuit the voltage is the same except for polarity in the two sides in a DC confirguration.

Edison encountered problems with power transmission more than a mile using direct current and finally discovered that he could achieve longer electrical transmission over lines more than a mile by using alternating current.

ummm errr.. Tesla was the one who knew of the AC being a better source of power over long distances, thus the reason Edison fought so hard to show the public that AC was a far more dangerous choice than DC.
Edison electrocuted ( till dead) an elephant with AC to prove the dangerous nature of it... basically all he did was cook it while it was alive

 

[sonicbomb]

@Bunnykiller
Edison used a vacuum too and I doubt that he was using voltages in the keV range. So your supposition is that it was down to poor quality tungsten and using DC rather AC?

Edison was a bit of a pirate wasn't he.

 

[Bunnykiller]

Per the Autistic husband:

The amount of force it takes to push/draw the current through the material is what matters. The material causes friction which is the impetus for the splitting off of the electrons.. You lower the amplitude (a smaller wavelength) and you you have less friction because amplitude is a wave form and it passes through less material or space/time at a higher amplitude or straight line. thus in order to acquire a lower amplitude you change the material you are passing the electric current through. I.e. Halogen light bulbs, LED light bulbs, Neon lightbulbs, florescent tubes all contain gas instead of Tungsten except for the LED which is a crystal container.

Furthermore, improving the container that all of this action/reaction happens within eliminates contaminants that also cause friction. Keep in mind, that all the action/reaction happens at the center between the two polarities. Thus, again, allowing a lower amplitude to create the reaction/action.

Synopsis: Bigger is not always better, faster is not always quicker, and brighter is not always fancier, either. There may actually be less stuff involved.
|
Brought to you by Autistic Husband who knows everything.

I got nothing. I wanted to see if he did. Do let me know if it's correct @sonicbomb

amplitude is the power/strength of a signal, the height of the peaks and valleys of waves in the ocean for example. Frequency is the number of times the amplitude peaks in a moment of time. the substance which the power is being put thru is either conductive or insulative. A conductor is used to allow the power ( lets use volts/electricity) to travel thru it ( a wire) metals are better conductors since they usually have the outer electron shell incomplete ( not filled to the 8) and will easily pickup and release extra electrons pushed into its electron orbit area by voltage applied. An insulator has a full or nearly full electron orbit shell and is resistive to picking up or releasing electrons thus inhibiting voltage flow. So, an insulator is a really good resistor. A resistor is a material that is an insulator mixed with a conductor, for example clay and carbon powder. Or a resistor is a conductor designed to minimize the flow of electrons via mechanics, for example a thin wire is a good resistor.

okaayyy to tackle the above, to create Thermonic emmisions one needs heat, enuf heat to excite the material being heated to vibrate fast enuf at the molecule level along with a voltage gradient high enuf to shake electrons free from the orbit. The higher the voltage ( amplitude) increases the potential to shake loose some electrons, the frequency needs to be fast enuf ( the waves close together) to not allow the electrons to settle down ( think of shooting a gun, you pull the trigger and bang the gun jumps and you move a little) a low amplitude low frequency source would be like shooting a 22 once a second. A hi amplitude hi frequency source would be like shooting a full automatic 50 caliber machine gun which fires at 10 times a second ( for example) for as long as the gun is fed ammo( its strong enuf to move you backwards and push you down). Once you have the electron loose and its being kept loose, it finds its way to the positive ( anode) pole. If there are any contaminates in the container, the electron will want to attach its self to it and then off both the contaminate and electron go towards the anode, thus darkening it. A hi voltage and high frequency has a better chance of creating thermonic emissions. As I mentioned before, noble gasses are decent insulators... up to a point, once that point is reached, the gas no longer is insulative but now conductive in a plasma state ( this is why neon glows). To get to that point the voltage needs to be strong enuf not only to shake loose an electron and let it carry over to another molecule, but to keep it suspended for enuf time to gain enuf power to release it when the electron does fall back into place. When it falls back into place, the energy it was holding onto is released as a photon... thus the glowing neon.

 

[Bunnykiller]

@DaveP
Understood. The question is why do we not see issues caused by the thermionic effect in modern light bulbs.

lack of contaminates, tungsten instead of carbon, better vacuum, and several other minor improvements I dont remember at the moment ...

 

[Bunnykiller]

@Bunnykiller
Edison used a vacuum too and I doubt that he was using voltages in the keV range. So your supposition is that it was down to poor quality tungsten and using DC rather AC?

Edison was a bit of a pirate wasn't he.

the difference of 2 magnitudes in vacuum makes/breaks the filament and 2 mags of difference of vacuum is really close together on the torr scale.

and yes Edison wasnt what one would call very moral. He killed an elephant just to show that AC isnt "safe". 140VDC isnt safe either.

 

[Bunnykiller]

Mornin All...

 

[DaveP]

Post deleted by DaveP

 

[DaveP]

Morning @Bunnykiller

 

[stols001]

I have not spoken with the husband further so now I would like to present my own answer: magic.

LOL my son got all obsessed with Tesla for a while there (the dead guy) and he built a small Tesla machine/oscillator for 7th grade Science class project. It worked, no one died. Man. So like, well, I wish he had that initiative today he is currently laid off and playing video games, pretty much.

I'm not saying a return to building Tesla machines is the way to go, but gee SOMETHING.

Pardon the digression.
Anna