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Posted November 11, 2007 5:01 PM
Pathfinder Tags: challenge questions

The question as it appears in the 11/13 edition of Specs & Techs from GlobalSpec:

Electrons are ejected from the surface of a metal plate exposed to light with wavelength . A uniform, retarding electric field E is imposed on the plate, and it is observed that the ejected electrons do not travel more than a distance d from the surface of the plate. What is the threshold wavelength for the plate material?

(Update: Nov 20, 8:49 AM EST) And the Answer is...

The threshold wavelength is defined as the minimum wavelength capable of ejecting electron form the metal plate. This wavelength, , is a material property.

When light of wavelength impinges on the surface of the plate the ejected electrons will acquire a kinetic energy equal to

(1)

When the electrons move in the direction of the retarding electric field and reach the maximum distance d, all this energy is converted into potential energy given by

(2)

Equating equations (1) and (2), we get

(3)

Solving for we get

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#111
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Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/16/2007 1:14 PM

Now you've put me off the idea completely.

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#113

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/16/2007 2:07 PM

Fyz doesn't like to share!

ROFL

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#115

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/16/2007 2:57 PM

How uncharitable. Crooning is enough to put any self-respecting man off his food - it's even worse when executed in a raspy voice. So far as I'm concerned, if it resembles any kit-kat I've ever seen, you're welcome to the whole thing. How's that for generosity?

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#119

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/16/2007 3:40 PM

Well that's no fun ! ( I'm exempt, being obliged to the Tufty Club)

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Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/16/2007 10:46 AM

I feel sorry for you now, over here we have normal Kit Kat in 2 or 4 sticks, orange, mint, white or dark chocolate, chunky Kit Kat & chunky peanut butter Kit Kat.

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#104

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/16/2007 11:01 AM

Oh, I never said we did not have the other variations as well, though I am not sure which ones. I was just commenting on the "special" orange-colored bar and its disappointing taste. I believe I have seen the dark and white variations, also the oversize bars and ones with caramel, although I prefer the TWIX bar for a chocolate/caramel/cookie bar.

I also enjoy "Snickers" by M&M/Mars, especially if refrigerated or even frozen (but you need very good teeth to enjoy the frozen ones!). Frozen M&M's are good as well, plain or peanut. Makes them crunchier!

I have to admit, though that my favorite candy is not chocolate at all, but a peanut covered caramel fudge called PAYDAY. A "Pay Day" and a coke. What we used to call in the Air Force, the "fighter pilot's breakfast"!

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#106

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/16/2007 11:17 AM

Excuse me for ignoring the delights of PAYDAY, but do you guys real get Twix ? Wow - have some Kudos, how mad is that > 'Snickers' used to be our 'Marathon.' You Americanised us !'

Cadbury vs Hershey ? what'dya say ? The Quakers will get mad........

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#107

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/16/2007 12:11 PM

You Americanised us !'

Heck, we have been doing that for a long, long, time! Are you enjoying your McDonald's and Wendy's Hamburgers? I had a Wimpies (not an American chain) when I was in England and thought it was horrible! Of course, I am not a big fan of McDonald's either!

One of my favorite old movies is "The Americanization of Emily" , filmed in 1964, but the setting was 1944, which teamed James Garner and Julie Andrews, with on-screen chemistry that would not be re-captured until years later when "Victor/Victoria" reunited the two. James Garner even called this his favorite of all of his movies.

Cadbury vs Hershey ? what'dya say ? The Quakers will get mad........

Who, these guys? They've "gone Hollywood"!

Seriously though (if that's possible, given the subject of this sub-thread), the Quaker Oats people do quite well with their line of Chewy Granola Bars, several of which are chocolate covered or contain chocolate chips/bits.

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#117

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/16/2007 3:26 PM

They told you those little brown bits were some sort of confectionery ? Sort of small, brownish and round ? Ever seen a squirrel hopping around the garden ?

Wimpy is a complete and utter 'yuck'. I like some of the brand rivals (on occasion) but have to admit that we Brits couldn't' assemble a burger any more than we could a B2. Anything reassembling fresh salad would be banned, and tomato sauce would be compulsory. Mustard etc ? Not a chance. Meat in the 'burger' ? - you've got to be joking. There's more meat in a 'Donner kebab' ( ref to Brit high streets, approx 11 pm).

On a historical note, the incidence of quaker belief and enterprise is quite fascinating. Many of the major brands are so linked. I've no idea or concern whether that carries meaning, but it is curiously interesting.

One of my fave film lines ( Empire of the Sun) : " Hey kid, would you like a Hershey Bar ?..". So would I kid, have you got one ?" It tags in nice with "B52 Cadillac of The Sky". All-American .

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#156

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/19/2007 4:31 AM

You should try one of Ahmed's Greedy Burgers from our local mobile take away, 2 burgers, with cheese fried egg & mushrooms. Don't ask for extras unless you have a very large mouth.

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#161

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/19/2007 10:30 AM

That almost sounds good ! I once did 3 stotties (the full breakfast variety), though my stomach didn't half ache afterwards. It was one of those things that happens after a seriously heavy night out. At some point the next day nausea go's and hunger re-appears.

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#163

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/19/2007 11:53 AM

3 full 8" stotties each filled with the standard 2-rashers of bacon, an egg and a full-fat Tyneside sausage?

Didn't half ache? Would that be a full-on triple-strength knobs-on tummy ache?

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#166

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/19/2007 1:04 PM

It was fair-bad. My Geordie mate even looked on with pure horror on his face. Up there it's something of a delicacy, to be savoured with a glass of 'broon'. Even the woman in the shop said to me ' Are you sure?'. All I can say is that I'd just got over a seriously bad hangover, and felt hungry.

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#169

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/19/2007 4:18 PM

The only time I've ever felt that hungry was after a 1960's anaesthetic had worn off. The nursing staff said it was far too soon to eat, but one of the doctors looked at my vital signs (whatever those might be) and said I could be allowed a half-pound steak with a few boiled potatoes (undercooked as it turned out) and steamed veg. (That would have been barely about enough for a light lunch at that stage).

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#170

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/19/2007 5:18 PM

That is indeed interesting to hear. Be pleased that you got some meat. 1960's ,post car crash- I got none of that. A few bruises etc is nothing compared to the rest. Seat belts are a good idea.

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#171

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/19/2007 5:39 PM

That was corrective surgery for a childhood injury - so they already knew me. I doubt that there would have been that much flexibility in the trauma departments.

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#168

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/19/2007 3:51 PM

Ta for the link to h2g2 - I listen to BBCR4 most of the time (at least it's on in the backgound while I'm working), but I missed out on this.

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#157

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/19/2007 8:59 AM

There's more meat in a 'Donner kebab' ( ref to Brit high streets, approx 11 pm).

I sure am glad you added the parenthetical reference! The only "Donner" reference I was aware of was the story of "The Donner Party" disaster, which involved a wagon train heading west to California in 1846, trying to get through the Sierra Nevada mountains via the now infamous "Donner Gap" (named for them). It seems the party got snowed in, ran out of food, and it being winter in the mountains, no wild game was available either. They ended up starving (38 of 87 died) and there were reports of cannibalism (of the already dead only), hence a "Donner kebab" would have a whole different meaning in that context!

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#160

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/19/2007 10:20 AM

I am now feeling distinctly queazy !

(No, 'distinctly queazy' in not a chum, just a sort of bilious thing)

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#126

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/16/2007 11:44 PM

I liked his speech about being a coward.

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#129

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/17/2007 8:57 AM

Until you've watched Jack Nicholson in "A Few Good Men", you're just letting the best in life pass you by.

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#155

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/19/2007 4:25 AM

I don't know Payday but I love the Reese's peanut butter cups although they're not easy to find. Occasionally, when the lusting becomes overpowering, I will go to a site like Cybercandy & buy a large assortment of the things I can't easily find.

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#105

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/16/2007 11:11 AM

chunky Kit Kat & chunky peanut butter Kit Kat

Good grief you need help ! Even with my proclivities I feel sick. Seek a therapist. Urgently ! My god, you'll be asking for jam on it next. Next you'll be telling me you don't enjoy playing with the foil bit of the wrapper. Flicking it at work colleagues or cats. Oh, you poor degenerate sod. The humanity........

< If Rowntree would like to pay me enourmous ammounts of money for this promotion, then do so via CR4. They will tell you to ****- off as money grubbing ******, but a % would still be nice)

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#125

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/16/2007 11:40 PM

I thought the Brits always had a fried egg topping their Kit-Kat bars?

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#127

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/17/2007 5:44 AM

You're getting it all wrong, there. We batter'm and deep-fry 'em.

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#128

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/17/2007 8:53 AM

Any self -respecting Brit cafe employs a special person. Their only job is to lovingly place a hair across your fried egg. If visiting here, don't be surprised by this, and never complain unless it is short & curly or does not match the hair of the waitresses. The hair will usually be found draped across the yolk, although some establishments do try to place it beneath the egg.

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Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/17/2007 2:46 PM

Kris warns: "Otherwise some Sud will bury you (and I don't mean Darth Vader !)."

-----

Holy Naked Neutrinos, Batman! It's the (heavy-water PMT support core of the) Sud-bury (Ontario, Canada) Neutrino Observatory!

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#132

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/17/2007 3:09 PM

Oh the shame, the pity....

My god man, it's Canadian ! Now I'm coCERNed about our well-being.

ROFLMAO !

( Unless you were a scrptwriter for Southpark, you couldn't make this stuff up !)

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#134

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/17/2007 3:44 PM

Holy Hoppin' Hadrons! Now, Squire, mightn't you be thinking about the dark predictions of tiny black hole, strangelet and monopole production at the LHC?

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#135

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/17/2007 4:18 PM

If they smash their little balls, will it happen in Switzerland or France ? I'm worried man ! The picture was Canadian so that doesn't matter. OMG the duality of it all !!

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#136

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/17/2007 4:54 PM

ROFLMAO ???

OK so I'm an ignorant old bugger, but how can I be expected to intuit (or even remember) all these daft acronyms?

Yea, so Google told me, but can someone in CR4-Land dream up a system so that:

1) Anyone using such a device can add it to a database, and

2) Right-clicking (or as you will) on the character sequence will bring up a definition?

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#137

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/17/2007 5:11 PM

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#138

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/17/2007 5:43 PM

But why should I have to ask?

OK, if I'm reading something special (e.g. A Clockwork Orange, or a technical paper), I agree it's fair enough to have to flick back to the glossary every now'n again, but in general conversation using the (apparently) accepted language of the site (English?), I reckon this kind of thing doesn't help folk to follow what's going on (certainly doesn't help my tired old brain). It's like scattering "in" jokes all over the place (which is OK if you've been following the discussion and can get some kind of handle on what's going on, and the jokes are either explained within the thread, or it can be assumed that the majority of the readers will cotton on), but encrypting them in an "in" code. Multiple obfuscation.

More !

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#139

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/17/2007 5:48 PM

ACRONYM = Alphabetic Co-location for Reducing Or Numbing Your Memory.

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#140

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/17/2007 5:55 PM

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#158

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/19/2007 9:19 AM

When I was a Manufacturing Engineer in the Automotive Controls industry, we often had machine malfunctions that would stop the assembly of our products. We would often refer to this unexpected machine stoppage as a "crash". Our boss did not like the term "crash" because that implied that there might be some serious damage to machine or operator, as in a motor vehicle "crash". Therefore he outlawed the use of the term "crash" in production status reports.

In our next meeting I reported that one production line had been down because one of the machines had executed a C.R.A.S.H., or "Completely Random Accidental System Halt".

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#159

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/19/2007 9:24 AM

Yes!

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#162

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/19/2007 11:45 AM

"Often had machine malfunctions" - and your manager was worrying because you called it a crash! Did that part of the company survive?

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#164

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/19/2007 12:26 PM

SFIK the company is prospering and doing quite well. The same may not be said for said manager!

ROFL

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#165

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/19/2007 12:38 PM

He probably moved on to a senior job in another company which was in the process of being taken over, and received a fat redundancy cheque for expediting the negotiations. After that, he was headhunted by a VC company and has recently taken very early retirement. He is now rubbing along on a fat pension and the proceeds from half a dozen non-executive directorships.

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#167

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/19/2007 3:18 PM

You windin me up pal? Wanna come outside n say that?

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#144

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/18/2007 7:53 AM

Apologies, you're quite right, it's a picture of Sudbury. But what I've in seen before looks much more polished - it must be the lighting or something.

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#147

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/18/2007 8:39 AM

It must be the mirror that confuses.

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#149

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/18/2007 8:58 AM

Are you referring to the pictures of the PM tubes reflected in the acrylic. If so, I've seen those too, but they are not what I was referring to. I suspect different lighting or pale-coloured surround to keep off dust during works, but I wouldn't swear to anything

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#150

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/18/2007 9:02 AM

.......****-that. It sounds teknikal. I would.

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#58

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/14/2007 8:14 AM

I believe the question has been answered as intended by (guest in post #2 and explained by Europium). But many real photo-cathodes don't behave like that. Take for example a GaAs-Cs photoemitter. The process of photo-emission is (roughly) as follows: first the photon transfers the electron to the conduction band; the requirement here is that the photon energy exceeds the bandgap potential. As this material has "negative electron affinity", the electron accelerates as it is emitted from the surface. The additional kinetic energy this imparts would need to be added to the initial number. Unfortunately, this is by no means the whole story, as any surplus photon energy is divided between the generated electron and the hole. Then there can be systematic directional effect - there can be a minimum lateral component to the kinetic energy in some material (this would only apply where the photoemitter grows in a systematic crystal orientation on the surface). And we are still considering a direct-gap emitter. Indirect gap semiconductors share energy with the acoustic lattice (phonons)...

Apologies that the terminology and explanations are not ideal - it's complex and not really my immediate field.

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#62

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/14/2007 1:06 PM

Perhaps the following would be less bad??

The question specified a metal plate; if we read that as meaning a true metal, the calculations are based on all the photon's energy being transferred to a single electron that is already in the conduction band. Issues with conservation of momentum mean that I don't understand how that can happen (that doesn't mean it can't**, just that I haven't appreciated the appropriate conditions). However, if it were to happen, the calculations would be correct, as some of those electrons would be emitted perpendicular to the surface, and the calculation would then give you the value for the electron affinity of the material (which has to be overcome before the electron can enter a vacuum)

Although this doesn't correspond to the question, I expect you can also get close with a direct-gap semiconductor, where the photon generates a hole-electron pair, particularly if you choose a semiconductor with heavy holes and light electrons (and the bandgap is large compared to the residual energies). The equations could then come close when the surface has positive electron affinity. Where the material is designed for efficiency of electron ejection, however, the surface will exhibit negative electron affinity, and the electrons will be accelerated as they leave the surface. The energy this provides would need to be included the calculations.

Indirect-gap semiconductors introduce yet a further level of complexity, due to the phonon energy and momentum that are involved.

**Indeed, if/where it is practical, it would certainly be a convenient method for measuring the work-function of a material - perhaps this is where the question comes from?

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#73

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/15/2007 1:02 AM

Why not go back to what Einstein was using when he did his famous experiment regarding the particles nature of light (I think he got a Noble for this one). His metal was cadmium. He increased the intensity, which increased the number of electrons ejected, but not their energy. To increase the energy of ejected photons, he had to increase the frequency (energy) of the photons.

I think this is easier than taking on all the additional stuff you need to take into account when using complex semiconductors.

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#76

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/15/2007 4:18 AM

Indeed. But SFIK, although there is a threshold, the peak energy imparted to the electrons is not 100% of the energy of the photon, which is what these calculations assume. The reason is that some of the energy has to go to the lattice to allow momentum to be conserved - I'm just not certain of the proportion.

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#88

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/15/2007 6:05 PM

Check here as a starting point - I think the energy you're looking for is the Electron Work Function.

Good luck!!!

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#92

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/16/2007 4:58 AM

You* are not reading what I mean. I've no problem with the work function**, as the energy required to overcome it leaves the electron without momentum. The issue is with the photon energy that is surplus to overcoming the work function; the calculations (guest, Europium, etc.) assume that all of this additional energy is transferred to the electron as kinetic energy, and my point is that conservation of momentum means that equal and opposite momentum*** has to go somewhere, and some energy must be associated with this momentum.

I hope that is now clear.

Fyz

*How many of you are there? Can vermin read? How come your avatar only shows one of you?
**I called this the threshold on the basis that the term is both correct and should be understood
***There's also the momentum of the photon, but that is relatively small

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#112

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/16/2007 1:43 PM

You may not have to worry much about ***. Considering that photons have no rest mass.

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#114

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/16/2007 2:53 PM

Still trying to confuse the innocent?

In case you were beginning to be successful, zero rest mass doesn't mean zero momentum. The momentum of a photon is E/c = h/λ = hν/c (ν is meant to be nu, for frequency; I'd have preferred curved edges, but what you see is what CR4's symbol generator provides). As I implied, for light (the stuff you can see or thereabouts) it's rather small (less than 1/100,000 of an electron's momentum at similar kinetic energy).

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#118

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/16/2007 3:34 PM

I'm going to snitch you two up to jorrie soon ! You're making it jolly dashed hard for idiots like me. In my mind ,momentum and stuff is what happens on the end of a sledge hammer. Now I'm all confused. Do it in layman's terms please.

< I always think that if you can't explain something, it's because you don't fully understand yourself>

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#121

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/16/2007 5:33 PM

Ultra-miniature sledge-hammers, but moving very fast. (But bar billiards really is a closer analogy.)

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#123

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/16/2007 5:51 PM

Is that the one with the 'mushrooms' on the table ? Nah, pool is a better comparison. The mushrooms fall in very hard to predict ways. I used to play ' Cherries or Bananas'. Sometimes I do snooker - once I saw a ball cannon into a pocket, roll along and fall down the pocket at the other edge ! Honest -it only happened once, but it was way cool. Nobody ever believed me and my mate who played the shot.

His wife wasn't happy when I took his jacket home one day. Don't know why. I just said I found it at the bottom of a mine shaft. Telling her he was in it didn't seem to alleviate her upset.

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#124

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/16/2007 11:33 PM

It sounds as though you believe that the photon "bumps" the electron from its shell about the atom. I don't think this is quite right. Just seems to me that a photon imparts energy to an electron in more of an electro-magnetic fashion.

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#130

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/17/2007 2:02 PM

Where on earth did I imply that? What I said was that momentum must be conserved. I mentioned the photon momentum only in passing, and also said in the first posting that it was insignificant. In the posting to which this was a reply, I said that light (the photons that were likely to be relevant) it would represent in the order of 1/100,000 of the momentum of the electron. I cannot think of a more clear way of repeating that it is insignificant. Are you just trying to avoid turning your mind to the actual issue I was addressing: I'll reword it just in case there's still a problem:

If an electron is emitted with kinetic energy, it must have acquired momentum. Unless there is another source for this momentum**, the object from which it comes must acquire equal and opposite momentum in the interaction. That means the object that emits the electron must move as a result of the emission of the electron, and so absorb some of the energy that caused the electron to be given off in the first place. This applies to kinetic energy only - not the work function.

Additional note: the electrons emitted are in outer orbital shells, so we cannot expect the coupling to the much heavier nucleus to be very large; that is why I expect (but don't know for sure) that a significant portion of the excess energy will be absorbed by the lattice. That is certainly the case for semiconductors (about which I do know a little), where excess energy (beyond the band-gap) is at least partly split between the electron and the hole, according to their effective masses (indirect bandgap semiconductors also have significant lattice effect).

**The only possible "other source" for this momentum is the photon, and it's momentum is tiny.

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#133

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/17/2007 3:11 PM

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#142

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/17/2007 11:17 PM

Now, now don't get upset. It's OK, and don't listen to that nasty, little squirrel making reference to your mother... I'm sure she was a very fine and upstanding woman.

Here, just stare at this for awhile, and ask yourself where is the momentum...

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#143

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/18/2007 6:07 AM

I keep coming back here, so the momentum definitely exists.

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#145

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/18/2007 7:56 AM

That was more than a few momentums (momenta?)

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#148

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/18/2007 8:43 AM

'momenti ? I ain't a physicist, but I've seen that gif before.

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#151

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/18/2007 9:05 AM

The plural of momentum (Latin neuter) should be momenta. I think that momenti would exist in Italian (as the genitive), but that's outside my linguistic sphere...

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#152

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/18/2007 10:31 AM

So who has erred ? Probably nobody but a lonely sheep farmer in Wales.

<Cetacia, just shut up.>

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#153

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/18/2007 1:25 PM

Sheep farming?? Yee-ouch

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#154

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/18/2007 2:54 PM

Shaping people is my biz. You've no idea how I do this. I love you in ways you can't imagine.

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#69

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/14/2007 8:09 PM

metal plate with a magnet on it!

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#70

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/14/2007 8:15 PM

A + d =Ao

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#141

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/17/2007 11:11 PM

If

λ<λ0(only then will electron cross threshold)

initial velocity of the elctron(u) = sqrt[{2hc*((1/λ)-(1/λ0))}/m]

fianl velocty(v) = 0

distance covered = d

use (vsquare) = (usquare) + (2*d*(acceleration))

where accleration is = e*E/m (e is charge and mass of electron)

to get

(1/λ0)=(1/λ)-(eEd/[hc])

in terms of constants and known variables!

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#146

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/18/2007 8:04 AM

That looks suspiciously like post#2 "λ0 ≈ 1/(1/λ-d.E.q/c/h)" and its followers. But what reason have you for assuming that all the excess energy (over and above the work function threshold) ends up as kinetic energy in the electron, rather than heat in the lattice?

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#172

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/21/2007 6:10 AM

(Update: Nov 20, 8:49 AM EST) And the Answer is... making unjustified assumptions

Fyz

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#173

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/21/2007 8:30 AM

On what planet

1/λ0=1/λ-eEd/hc

becomes

λ0=1/λ-eEd/hc ???????

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#174

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/21/2007 10:56 AM

Misprint alley, Manchester?

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#175

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/21/2007 2:25 PM

Note, he did use parentheses. I guess he meant:

λ0= (1/λ-eEd/hc)-1 although, I admit, I have NO IDEA what that formula means, but I can do algebra!

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#177

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/21/2007 6:49 PM

Hi STL,

I feel better, at least, in spite of my solution taking the long road. Specs & Techs made the same mistake I made (ie, failing to invert Eqn 14) at the end of Post #30. Wonder if it's hereditary. I have relatives living in NY state. Maybe one of 'em is working for GlobalSpec incognito.

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#176

Re: Ejected Electrons: Newsletter Challenge (11/06/07)

11/21/2007 6:37 PM

1/λ0 = 1/λ - eEd/hc

1/λ0 = (hc - eEd)/hcλ

λ0 = hcλ/(hc - eEd)

Small world.

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