what causes striation patterns? (1 Viewer)

[Giant Lobster]

the syllabus is stupid. they basically ask you to "notice" that there are striation patterns caused by cathode ray tubes, but doesnt tell you to understand the cause

well I anyway Im curious as to why. Anyone know?
I couldn't figure out why they occur in patterns and not homogenously; that should be the case if the electrons exciting the low pressure gas was producing the "patterns". hmm

 

[xiao1985]

this is jsut a guess, i don't know the answer either:

prolly cuz electron, bein a matter, also exhibit wave properties accordin to de broglie... there fore it will have like an amplitude and like period as such... assuming electrons in the cathode ray would have similar wave length, and at different amplitude the electrons' ability to excite atoms varies... that's y the striation patters???

 

[Affinity]

it's because moving electrons need to reach a certain speed before they can pass energy electrons in the gas atoms, and they must pass energy in chunks

 

[Giant Lobster]

Originally posted by Affinity
it's because moving electrons need to reach a certain speed before they can pass energy electrons in the gas atoms, and they must pass energy in chunks

Yeah thats what I thought
but then if that were the case, why do the patterns remain in their place? shouldnt they be everywhere?

Say between every stripe theres 4 cm, then according to that theory i can say the electrons need 4 cm to regain enough speed to pass their energy on the gas again. So that explains why the patterns are all separated by 4 cm. But what i dont get is why the patterns seem not to vary from their position? It should flicker and go everywhere but it doesnt

 

[t-i-m-m-y]

*whats going on?

i'm not sure but isn't it the energy difference in electron orbitals (or radial probability distribution plots hehe) being emitted within the visible light part of the EM spectrum?

 

[Giant Lobster]

come again?

 

[t-i-m-m-y]

haha lol did i lose u there?

it was about quantum physics and energy levels thats all, no big deal u'll learn it soon

 

[Giant Lobster]

yeh i know about quantum physics (as required by HSC level plus a bit more anyway) but what you just said there was basically:

"visible light is produced by gas in cathode rays"

correct me if im wrong please

 

[t-i-m-m-y]

yep pretty much. the energy diffrence emitted is in the visible light spectrum

 

[Giant Lobster]

yeh but then that explains why cathode rays emit light, not why the weird patterns occur

 

[t-i-m-m-y]

are u guys talking about how the "patterns" are formed, and not the light itself?

 

[George W. Bush]

I have a 2 page exerpt from a university physics book on the subject. If you care enough, I'll see if I can post the major points.

 

[t-i-m-m-y]

Originally posted by George W. Bush
I have a 2 page exerpt from a university physics book on the subject. If you care enough, I'll see if I can post the major points.

post please!

 

[George W. Bush]

Will do on Monday, weekend obligations et al

 

[cko]

isn't it because the electrons hit atoms and the atoms get excited and light up? and then the electrons move along the tiube and gain more energy until they have enough to hit the atoms again?

 

[The Bograt]

Yes the electrons reach a certain velocity before they hit a gas atom. As the pressure decreases, the spaces between the atoms increases, meaning more distance for the electrons to speed up. As soon as they have enough velocity and hit an atom, they produce light. The electron is absorbed by the atom, but knocks off another electron, which must speed up again before it hits another atom.
Use my expert analogy: A footballer runs, speeds up, and tackles a tackling bag, as he tackles the bag, a new footballer breaks out of the tackling bag and starts running at the next tackling bag.

 

[twiddla]

I believe the reason that the striations occur only in certain points is because the light is caused by electrons knocked to outer shells then dropping back down - when the cathode rays hit these atoms it slows the cathode rays down, to use the previous analogy, if you charge and hit a player, the speed you had reached before the player is lost and you must accelerate once more to hit another tackler with same kind of power.

 

[LeeScoresby]

Once the electrons reach a high enough speed, they eventually collide with a gas particle and the energy from the momentum converts into light. The electrons then lose their energy and therefore emit no light, hence the dark natured gaps. After this they speed back up and start all over again. Any questions???

 

[04er]

Originally posted by LeeScoresby
Once the electrons reach a high enough speed, they eventually collide with a gas particle and the energy from the momentum converts into light. The electrons then lose their energy and therefore emit no light, hence the dark natured gaps. After this they speed back up and start all over again. Any questions???

exactly

 

[Giant Lobster]

again, with that speed gain theory, it doesnt explain why striations occur
think about it like this
if millions of electrons are in the tube at any instant, and their velocities are all different, assuming that they do need to reach a certain speed before passing energy onto atoms, they will do so in no specific pattern. The result being light emitted homogeneously, instead of in stripes. That's what i dont get.

I know the electrons do need to reach a certain speed, yes. But why do they all do so at specific areas? The probability is just too unlikely. George W. Bush can you pls post your uni notes on this matter?