The h Bar

31 1 4

Obe changed his name but not his color :D

How is hydrogen gas ionized in a discharge tube? I always believed that the electrons used to ionize the gas molecules but I am not able to think of any mechanism for that.

@YashasSamaga There are several ways

Have you heard of breakdown potential?

ACuriousMind

@BernardoMeurer why're you asking me? I didn't even really know he was "gone" (and his account still exists)

Bernardo Meurer

@D3075 Yo, I need you

3:08 PM

@2017 dielectric breakdown voltage?

Bernardo Meurer

@ACuriousMind Because you know things

Electrical breakdown

Electrical breakdown or dielectric breakdown is a long reduction in the resistance of an electrical insulator when the voltage applied across it exceeds the breakdown voltage. This results in the insulator becoming electrically conductive. Electrical breakdown may be a momentary event (as in an electrostatic discharge), or may lead to a discontinuous arc charge if protective devices fail to interrupt the current in a low power circuit. Under sufficient electrical stress, electrical breakdown can occur within solids, liquids, gases or vacuum. However, the specific breakdown mechanisms are si...

@2017 I was typing "@anon" and searching for your name lol

A high displacement current will also do the job

Electron flow is nothing but current flow after all

The problem is here

"Regions of intense voltage gradients can cause nearby gas to partially ionize and begin conducting."

Wikipedia says that

My problem is "but I am not able to think of any mechanism for that."

3:10 PM

Let's see a basic problem: How do electric sparks occur?

I know that electric sparks occur because the electrons leave the material.

I don't know how a high voltage would cause an electron to leave its place.

@YashasSamaga No, it also ionizes the air in most cases

yea

how does it ionize?

5 mins ago, by Yashas Samaga

How is hydrogen gas ionized in a discharge tube? I always believed that the electrons used to ionize the gas molecules but I am not able to think of any mechanism for that.

I know that the gas gets ionized

but I don't know how

Using radiation makes sense; a high enough photon could knock the electron off the atom.

Any low or high electron density region attracts or repels the oppositely charge ions

but how do you do it with just voltage or electrons?

3:12 PM

Think of air as a dipole

I already thought about it

it sounds unbelievable

You don't ionize with electrons

Air is ionized due to lack or excess of electrons

wait a min

im coming

@2017 en.wikipedia.org/wiki/Electron_ionization

High voltage might polarize the atom but I seriously doubt if it could remove an electron from an atom.

ATHARVA

@YashasSamaga when a certain amount of potential is applied across the dielectric the electric field produced detaches the electrons in atom this is dielectric breakdown.

Ionization of this sort is not caused by positive or negative charges per say, but by an electric field. We can view the ionization as the electric field trying to accelerate the electrons and nucleus of an atom in opposite directions and ripping them apart.

@YashasSamaga

3:16 PM

huh

I know that applying a large potential difference across an electric ionizes it.

The question is how does it ionize it.

I don't know how many times I must repeat it.

If the gas is ionized using radiation, I can guess a mechanism. The radiation could knock the electron off the atom (photoelectric effect).

@YashasSamaga Yes that is one way

But the other way is by applying an electric field

omg

I know

the question is how does an electric field manage to get electrons off the atom

Isn't it just electrostatics? A positive charge tends to move in direction of EF

chat.stackexchange.com/transcript/message/35693023#35693023 This was an example of what kind of answer I am looking for.

And negative charge tends to move in direction opp to EF?

3:20 PM

@2017 That is what I thought but that sounds unbelievable.

It is just opp charges attract and equal charges repel...

5 mins ago, by Yashas Samaga

High voltage might polarize the atom but I seriously doubt if it could remove an electron from an atom.

You mean you don't understand why positive charges move from high potential to low potential ?

No.

I mean, I understand that

The only mechanism I can think of is high electric field moves the charges in opposite directions; hence separating them.

but I am not able to digest it

that high electric fields can split an atom

@YashasSamaga Why?

3:22 PM

I couldn't find a source which says that is indeed the mechanism

Oh, you need a source?

Ok lemme see

by source I meant reference

that mechanism does not explain why low pressure is required for a gas to be conducting

I can guess a reason that the knocked off electron gets captured by the gas if there are too many

but I have no reference to confirm that

Yeah, im searching for a reference. BTW how else are the ionization potentials of atoms found in chemistry?

ionization potentials is the energy needed

it does not require the mechanism

all methods use the same number

it is just a number

@YashasSamaga How are they calculated experimentally?

3:24 PM

I don't care about it and it is irrelevant

@YashasSamaga That's the thing you're missing!!!

The same mechanism is used to find ionization potentials of atoms

while finding the ionization potential

you put the gas in the discharge tube and apply a potential difference

the potential difference where the electrons come out = ionization potential

that still does not explain what the potential difference does to bring the electron out

Exactly!!! The same mechanism occurs there

Now why potential difference brings electrons out? That is just Columbs law

There is no mechanism

it just says what happens when something is done

it does not say how

You are not understanding my question

let me give an example what I am searching for

Mechanism ? It is just that positive charges attract negative charges and repel positive charges

3:28 PM

what you are currently telling is analogous to "if you send a photon of enough energy, the electron gets knocked out"

What I am saying is just Columbs law...

what I am looking for is, "if you send a photon of enough energy, the electron absorbs the photon, the energy with the photon is more than the binding energy of the electron-atom system"

I need reference for that

I understand that super high electric fields can polarize the molecule. That's how dielectrics even work in the first place.

But I cannot digiest that electrons get knocked out

you are applying just 10,000V in a discharge tube

Hmm, I see your point

Lemme frame it like this:

You're correct that it's not the high voltage itself which ionizes the atoms, but rather the free electrons accelerated by this electric field.

If extreme polarization is really the case, then I'll accept it but I need reference for it.

Applying a strong electric field causes the free electrons to accelerate. Collisions with bound atoms then result in electrons being ejected from their orbitals, which are accelerated by the field and go on to ionize yet more atoms.

Electron avalanche

An electron avalanche is a process in which a number of free electrons in a transmission medium are subjected to strong acceleration by an electric field and subsequently collide with other atoms of the medium, thereby ionizing them (impact ionization). This releases additional electrons which accelerate and collide with further atoms, releasing more electrons—a chain reaction. In a gas, this causes the affected region to become an electrically conductive plasma. The avalanche effect was discovered by John Sealy Townsend in his work between 1897 and 1901, and is also known as the Townsend discharge...

3:31 PM

17 mins ago, by 2017

You don't ionize with electrons

-_-

This is called electron avalanche

You brought in semiconductors now.

@YashasSamaga Read it fully before showing the -_- face.

ok

The phenomenon basically occurs due to free electrons acceleration in medium when high potential is applied

3:32 PM

electron collides with the atom

why does the atom's electron get knocked off?

The same reason why negative charge is attracted to positive charge

Also the electrons are free electrons which start the chain reaction

They are loosely bound

@YashasSamaga You want to know why electrons knock out other electrons? That is because their K.E. of accelerated electron s is much larger than the binding energy of electrons....

I already guessed it

but I need reference

Every page I open tells "electric field ionizes the atom" or "electrons ionize the atoms". That is not what I am looking for.

Electron Avalanche is the term. You can search it online.

I've learned about it while studying semiconductors.

I guess this is quite intuitive...

3:44 PM

Wiki just says "subsequently collide with other atoms of the medium, thereby ionizing them (impact ionization)."

which is no intutive

it does not mention a word about the underlying mechanism

such as the electron colliding with another electron and transferring part of its kinetic energy to it.

There is only one possible mechanism and that is that and accelerated electron knocks off bound electrons.

Source? I need to search.

Need source.

I have already made guesses but I cannot confirm it.

And I don't find it obvious to accept it easily.

Finding source for what can be concluded by common sense is a tough job :) I will try to search and let you know if I find relevant stuff.

common sense? huh

Q: What happens when an electron collides with an atom?

1

I was solving this question: Here is part of the energy level diagram of hydrogen: n=4 --> -0.85eV n=3 --> -1.50eV n=2 --> -3.40eV n=1 --> -13.6eV When an electron of energy 12.1eV collides with this atom, photons of three different energies are emitted. Show on the...

particle-physics energy atomic-physics

3:49 PM

@DanielSank Dude, they often don't even listen to the users and just make up nonsense excuses.

heather

what's a good LaTeX document class for scientific papers? (just generic ones; I'm practicing writing in that format, not writing for a specific journal) should have an abstract command, sectioning, etc.

45. Physics | Atomic Structure | Collision of a Hydrogenic Atoms by Collisions | by Ashish Arora

@YashasSamaga youtube.com/…

►

It shows the maths part

Of electron colliding with atom

I don't need it

I know that energy conservation still holds

you take initial kinetic energy of the electron + atom = kinetic energy of electron 1 + ke of electron 2 + ke of atom

It also shows that electrons can be removed from their bound state by colliding electrons

(which is what you wanted initially)

I know that electrons can be removed using electrons

I am just wondering what happens inside

3:54 PM

@YashasSamaga Inside what?

the atom

electron enters the atom

that is considered as collusion

what happens next?

I know that electron enters an (atom - some magic happens) then two electrons come out

It can collide with any electron or may even get deflected depending upon probability

I don't like the idea of colliding "electrons"

A: How do collisions of fundamental particles produce different fundamental particles?

If it hits an electron then it can excite it or if it is deflected then it can form X rays

Hmm, you need to think of them as wave phenomenon none of which have 0 probability

You are delving into Quantum Mechanics if you now ask me the maths for this wave phenomenon :)

Collisions are just wave interactions

If you don't want to think of them as particles hitting one another

6

A simple version of this is bremsstrahlung, i.e. an electron that decelerates and produces electromagnetic radiation / photons. By your reasoning the energy of the electron should only be able to go into other electrons: maybe it should radiate other electrons, maybe a single electron shouldn't l...

What is going on here

3:59 PM

@BernardoMeurer sup?

Here's a pdf on collisions in Quantum Mechanics which looks quite detailed (ymambrini.com/My_World/History_files/Born_1.pdf)

@YashasSamaga

@0celo7 Not JEE

@YashasSamaga Liar liar :P

ATHARVA

Hi everyone.

@2017 You don't get questions like these in JEE.

4:04 PM

@YashasSamaga Just joking :'D

Q: Could somebody survive a fall by jumping off an object shortly before impacting?

2

It’s hard to explain what I’m asking for, so I made a diagram: The person is falling. The person stands on a large object while falling (let’s say a part of a plane). Just before the objects hits the ground, the person jumps with great force. The person lands safely on the ground after he jump...

newtonian-mechanics forces newtonian-gravity velocity free-fall

all the answers are wrong there

wow

4 answers and all 4 are wrong

@YashasSamaga Are you satisfied now or still need source? :P

I am going to give up on that.

Better you do. It will be difficult to understand unless you take a QM course.

Hello

ATHARVA

4:09 PM

Hi

@ATHARVA, how are you?

@YashasSamaga Does radius of curvature of lens change with temperature? How do you calculate the change if you know the coefficient of linear expansion of lens? Will it be just $$R=R_o+R_o\alpha\Delta T$$? I'm not sure if that equation can be applied to radius of curvature.

That is a standard problem.

check bimetallic strip questions

I'm going now.

Ok

Hmm, I find no relation to bimetallic strips. However, it seems I can apply the coefficient of linear expansion equation to this situation.

taylortechassoc.com/?page_id=2238

@YashasSamaga It's also a duplicate ...

4:19 PM

@JohnRennie Need some help! Can $R=R_o+R_o\alpha\Delta T$ be applied for radius of curvature of lenses? Why or why not?

$\alpha$ is coefficient of linear expansion of the lens...

@heather Use the article class.

Scientific works often use the twocolumn option.

@2017 Um, er, good question. IIRC objects expand isotropically on heating, so the radius of curvature will increase in the same way as any other linear dimension.

Hello @JohnRennie

Hi Ramanujan

As you get into sectioning, etc. I recommend reading this.

4:23 PM

@JohnRennie, Where are you from?

@Ramanujan UK

who is @2017

wut?

@JohnRennie hello again

Anonymous

4:23 PM

@JohnRennie Thanks. It seems it is true for all kinds of linear expansions. However, I have never seen a mathematical proof for this!

@DanielSank greetings

@Ramanujan He's lying. He's from Omicron Percii 8.

@0celo7 yo

@0celo7 where did bernardo want?

@D3075 idk, link?

'Morning

4:24 PM

I talked to him yesterday

@SirCumference hi

Well, kind of late in the morning

@0celo7 Howdy

I shouldn't have played metal gear until 5 in the morning

@0celo7 chat.stackexchange.com/transcript/message/35692951#35692951

getting a late start to the day is always bad

@JohnRennie, what happens if alternating current is passed in the coil of the dynamo?

4:25 PM

@D3075 I will text him

okay I'm going to leave for 30 mins or so lmk.

@0celo7 Correct. Play a better game.

Want suggestions?

@Ramanujan that's an odd question. Do you mean you are running the dynamo in reverse i.e. as an electric motor?

@DanielSank metal gear solid 5 is pretty great

@0celo7 k

4:26 PM

what do you think is wrong with it?

@DanielSank I should be learning some math, so no thanks

I want to finish this thing

turns out there's a post-game

@0celo7 Oh, well, it's not Super Metroid, Nethack, or any of my other favorites

@JohnRennie, I am talking about the bicycle dynamo..

@DanielSank I have Super Metroid on my 3DS I think

@0celo7 It is rather excellent.

Consistently in everyone's top ten games of all time lists.

@DanielSank I binge a game about once every month or two

maybe that will be my next

4:29 PM

How do you pass current through bicycle dynamo? :P That is a weird question!

I knocked out Fallout 3 over the break

Right so, Super Metroid is far less bingeable than modern games.

It's not a game where just putting in hours means you finish it. You have to navigate a labyrinth.

@Ramanujan I don't think anything will happen if you connect an AC source to a bicycle dynamo. The dynamo will just get hot due to resistive heating. What did you think would happen?

@0celo7 well, maybe binging would work, actually.

4:31 PM

cave story?

^ Excellent

Absolutely excellent.

@DanielSank Fusion is certainly my favorite

@JohnRennie How does applying a large electric field across a gas knock electrons off the gas atoms?

@JohnRennie, I am not sure. But I guess there would be motor effect..

@DanielSank I beat it like 5 times in high school then I edited the sprites to make them all blue as well.

best game for sure.

4:32 PM

@SirCumference More than super?

@D3075 Did you ever make the hell run in under six minutes (or whatever the special time limit is)?

I managed it after many, many tries.

@DanielSank A little bit. I played Super after I played Fusion so the magic might have faded a bit

@YashasSamaga there are always a few electrons in a gas due to natural background radiation. When you apply a field you accelerate these naturally occurring electrons. Apply a strong enough field and the electrons will accelerate enough to ionise any atoms they collide with.

@Ramanujan You could rotate the magnet using an AC current. However, that defeats the purpose of a dynamo.

@DanielSank But still, Samus is far more controllable in Fusion.

@YashasSamaga This creates more background electrons, and those electrons ionise more atoms and we get a chain reaction.

4:34 PM

What happens when an electron collides with an atom?

I mean what happens internally

I know that one electron goes in and more than one comes out

but how does the fast moving electron manage to remove an electron?

@SirCumference Perhaps.

a collision between electrons is not a meaningful statement, right?

@JohnRennie, isn't the magnet movable in dynamo?

@DanielSank You played it?

@YashasSamaga Electrons repel each other because of their charge. If a high energy electron comes close to an electron in an atom it exerts a large force on it, due to this repulsion, and it literally knocks the other electron out of the atom.

4:35 PM

@SirCumference No, but Samus is pretty floaty in Super.

@DanielSank Ya should. It's kind of like Super, but better controls and a twist on things.

@JohnRennie So it is definitely not because the electric field was too strong that it pulled the electron and nucleus apart (polarized it way too much)?

@SirCumference k

Grabbing ledges, easier walljumps, etc.

@SirCumference Wall jumping was fine AFAICT in super.

4:36 PM

@DanielSank Wall jumping was really hard to get down in my case...

Ledge grabbing is in AM2R. I bet Fusion and AM2R have similar controls.

@SirCumference There's a delay between pressing away from the wall and hitting jump. That's the trick.

@DanielSank I mean yeah, I know that now

@YashasSamaga No, you'd need a ridiculously strong field to do that. Sit down and work it out some time. You need a field strength so high that the potential difference across the atom is of the order of the ionisation energy in eV.

Oh, gtg

@SirCumference Does Fusion have interesting sequence breaking?

That's the thing I like so much about Super.

4:38 PM

@DanielSank It's a bit more linear, but there are some things you can skip if you really want to.

@SirCumference I'll try it.

I didn't like how linear Prime 2 was.

For some reason, it didn't bother me in Prime. Prime was amazing for some reason.

@JohnRennie In a discharge tube the electron avalanche would be induced by free electrons generated by the strong electric field isn't it? Or else how would the chain reaction start? I guess that some electrons will indeed be ionized by the field (which have low binding energy)...and then they start knocking off other atom's loosely bound electrons and this process continues...

1 hour ago, by Yashas Samaga

you are applying just 10,000V in a discharge tube

you have just 10,000V

that was the main issue

@2017 no, the free electrons are a natural background due to background radiation like cosmic rays.

10kV was too less so I couldn't believe the polarization theory

4:44 PM

@JohnRennie So you mean there are free electrons floating around in air ? This is a new concept for me!

I suppose even thermal energy will create some background electrons. At room temperature thermal energy is about 100 times smaller than typical ionisation energies, but there will be a very small proportion of molecules with enough energy.

So cosmic rays ionize the air particles...I see...interesting

@2017 Yes, though the concentration of free electrons is very small. Unless you live in a lead box there are atoms being ionised inside you at this very moment.

Slereah

I live in a lead box

It's like a radio you can't switch off
There's no way to get peace of mind
I'd like to live inside a lead-lined room
And leave all this Psi Power behind
- Psi Power, Hawkwind

4:47 PM

wow :)

@2017 CBR is in the syllabus I think

Hawkwind - Psi Power (HQ)

►

I did know about this (somewhat) but never took into account cosmic rays !

An awesome album!

@YashasSamaga Yeah, I do know. I didn't take it into account while thinking of the discharge tube

Balarka Sen

4:48 PM

I've got this stuck on my head. Gr.

I felt the effects were too negligible.

@BalarkaSen Listen to it a hundred times :D

@2017 If you do the school experiment of making a cloud chamber with dry ice and alcohol you can see the traces left by the electrons created by cosmic rays.

4

Balarka Sen

@2017 That'll make it worse!

A: Could somebody survive a fall by jumping off an object shortly before impacting?

2

You won't survive even if you managed to jump from a platform before hitting the ground. The answers given by other users state that you need to apply a large force on the floor (or whatever) to save yourself. While it is certainly true that you need to apply a large force (impulse) to stop your...

that is getting spam answers

Balarka Sen

I can override it with something else if I want I guess

4:50 PM

I think it needs the protected thing?

@BalarkaSen That's the way to get a song out of your head. Proven strategy!

oh nvm it is marked as duplicate

I did not refresh

How to make a cloud chamber

►

@JohnRennie I'll definitely try :)

Can you answer duplicate questions?

marked as duplicate by John Rennie newtonian-mechanics 31 mins ago

answered 1 min ago

wth?

4:56 PM

I guess they started writing an answer before it was duped...

@YashasSamaga I think that's wrong as I'm fairly sure it wasn't 38 minutes ago that I closed the question. Maybe that's the time since the first clsoe vote.

@2017 even they started writing before it was marked as duplicate, the "Post Answer" button must stop them from answering?