Talk:Thermionic emission

Edison Effect vs. Thermionic emission

The term 'Edison Effect' seems very wrong to me; the term thermionic emission is the 'correct' term, I believe - certainly, it is the 'scientific' one.. Even the article says that it wasn't first discovered by him. I don't want to step on anyone's toes, but shouldn't the redirect be the other way around? -- James D. Forrester 02:45 Apr 24, 2003 (UTC)

I'm familiar with thermionic emission, and I've never heard it called the "Edison effect" before. Google searches:

• "edison effect" (http://www.google.com.au/search?q=%22edison+effect%22) 1310 hits
• "thermionic emission" (http://www.google.com.au/search?hl=en&ie=UTF-8&oe=UTF-8&q=%22thermionic+emission%22) 4570 hits
• "thermionic effect" "edison effect" (http://www.google.com.au/search?hl=en&ie=UTF-8&oe=UTF-8&q=%22thermionic+effect%22+%22edison+effect%22) 7 hits

The small number of hits on the intersection indicates that "Edison effect" usually refers to something else. Indeed, browsing seems to show that it usually refers to how brilliant Edison was in some way or another. I'll move the page. -- Tim Starling 03:07 Apr 24, 2003 (UTC)

Does the Edison effect really refer to thermionic emission in general, or to the conduction of electrons from one electrode to another, or to the property that it only flows in one direction, and can be made into a diode? Omegatron

Yeah, thermionic emission is a general term for electrons (or sometimes ions) being emitted from a heated object in a vacuum, and the Edison effect refers to the diode effect, from what I gather. This article is kind of about both at the same time. Maybe it should be split up? At least the two should be differentiated within the article. Omegatron 22:23, Feb 26, 2004 (UTC)

Reference? -- Tim Starling 23:06, Feb 26, 2004 (UTC)

the internet? i don't know. thermionic emission obviously refers to the emission of electrons from a heated element. the phrase "thermionic emission" has no connotation of conduction, one way conduction, or anything. it is just the emission of electrons, from the name itself. electrons are emitted from heated metal whether there is electricity going through it or there are other electrodes present or not. edison effect, on the other hand:

http://www-istp.gsfc.nasa.gov/Education/welect.html - edison effect is the property that current can be conducted from one electrode to the other

http://www.amershamhealth.com/medcyclopaedia/Volume%20I/EDISON%20EFFECT.asp - "a current generated by an electric field in a vacuum tube."

http://www.charlesedisonfund.org/TomEdisonBio/ch10.html - "the previously unknown phenomenon by which an independent wire or plate, when placed between the legs of the filament in an electric bulb, serves as a valve to control the flow of current."

http://www.acmi.net.au/AIC/EDISON_EFFECT_HOME.html - "But, when Edison connected the foil to the positive terminal of the filament, a small current was indicated by the galvanometer. This later came to be known as The Edison Effect."

http://teachingtreasures.com.au/sciencenames/thomas_alva_edison.htm - "He discovered that electricity would flow from the bulb's glowing filament onto a metal plate inside the bulb. This is known as the 'Edison Effect'"

those are just the first sites that came up when i searched for it. sure, internet searches are not conclusive, but it seems pretty obvious that edison effect has more to do with conduction through a vacuum by the emitted particles than the particle emission itself. i think they are sufficiently different concepts that they should be separate articles. Omegatron 15:16, Feb 27, 2004 (UTC)

Fair enough, go on then. -- Tim Starling 01:52, Feb 29, 2004 (UTC)

http://www.plexoft.com/SBF/T02.html says either effect can be called the Edison effect. Hmm... - Omegatron 17:54, Mar 3, 2004 (UTC)

GRR. this site http://www.uh.edu/engines/epi1323.htm says: "The [Edison] effect is this: in a vacuum, electrons flow from a heated element -- like an incandescent lamp filament -- to a cooler metal plate." to a cooler plate?? i thought it only depended on charge. a cooler plate would just not emit electrons, right? - Omegatron

Hmm... that's different. If you don't apply a field, the electrons will diffuse from the hotter plate to the colder plate, because the hotter plate emits more electrons than the colder one. It's a diffusion process, as opposed to the drift process observed when you apply a field. If there's both a temperature difference and an applied field, the currents from diffusion and drift would be added together.

Perhaps it would be better if we could find some more descriptive term for these processes, rather than naming them after the person who discovered them second. -- Tim Starling 03:18, Mar 6, 2004 (UTC)

So a negative hot sphere in a vacuum would become neutrally charged while its neighboring cold sphere would become negatively charged? Of course, then the hot sphere would radiate heat to the cold sphere until they were both at the same temperature, and the electrons would then diffuse back until the spheres were at the same charge, depending on the speed of each transfer... But what about the walls of the vacuum chamber? Where do the electrons go that aren't being emitted in the direction of another electrode? Is there a specific temperature required to get the electrons to start emitting (related to the work function, i think)? There are a lot of questions involved with this stuff that I can't find answers for online.

The term Edison effect is pretty established, so it at least has to be mentioned, though it is certainly a silly name. - Omegatron

In a copy of the 1924 "History & Operation of the Vacuum Tube" Professor J.H. Morecroft of Columbia University writes in a chapter about "Electron Evaporation" that it was known as the Edison Effect for 20 years but not used or understood until Flemmings work. The term "Edison Effect" wasn't used to describe anything other than an observation of what was to become understood as "electron evaporation" and later "thermionic emission". It seems to me that the edison effect story/section should just be included in the history part along with a note that thermionic emission was originally called electron evaporation in the day of its discoverers. -- equant 02:50 Friday, July 15, 2005 UTC

Guthrie vs. Guthrie

I thought I had mentioned this here already. There are two Guthries who may have discovered the effect, but I don't know which did it. Both were alive and in the area at the time, and worked on similar things.

• Frederick Guthrie - "In 1873 an English physicist and chemist Frederic Guthrie griped a bar with a glowing metal ball on its end and put it near a live electroscope. In that moment he could see, that the split gilding on its end have drooped: the electroscope was discharged! This accidental invention was the first step, at the other end there were the vacuum tubes and the photocells."
  • http://www.quido.cz/objevy/Elektronka.a.htm
• Peter Guthrie Tait - "In 1866 he started a joint project with the physicist Balfour Stewart on heating a disk which was rapidly rotating in a vacuum. This was a topic Tait came back to on several occasions throughout his career."
  • http://www-gap.dcs.st-and.ac.uk/~history/Mathematicians/Tait.html

Probably Frederick, but it isn't clear online. - Omegatron 19:03, May 27, 2004 (UTC)

Editorializing

I found this paragraph a little awkward to read the first time:

Edison built a bulb with the inside surface covered with tin foil. When he connected the foil to the lamp filament through a galvanometer, with the foil dropped to a negative voltage with respect to the filament, nothing happened (because the cold foil electrode was not emitting electrons). But, when he raised the foil to a positive voltage with respect to the filament, a small current flow was indicated on the galvanometer, as electrons being emitted from the hot filament were attracted to the plate, and completed the circuit. This one-way flow of current was called the Edison effect (although the term is occasionally used to refer to thermionic emission itself).

May I propose:

Edison built a bulb with the inside surface covered with metal foil. He connected the foil to the lamp filament through a galvanometer. When the foil had a more negative charge than the filament, no current flowed between the foil and the filament because the cool foil emmitted few electons. However, when the foil had a more positive charge than the filament, the many electons emmitted from the hot filament were attracted to the foil causing current to flow

Opinions?

The above was posted by User: Limbo socrates who didn't sign with his ~~~~.

Be bold. :-) -- PFHLai 22:21, 2005 Feb 13 (UTC)

Thx :) Limbo socrates 22:37, 16 Feb 2005 (UTC)

I like the proposed new text, but I wouldn't omit the last sentence of the original paragraph...

This one-way flow of current was called the Edison effect (although the term is occasionally used to refer to thermionic emission itself).

Equant 20:48, 7 Mar 2005 (UTC)