b.tchy question - syclotron or whatever (1 Viewer)

[walla]

F=ma is only relevant if you point out that a=(v^2)/r
because that's where you get the need to increase field as velocity increases. ideally you combine them:
mv^2/r = qvb
b=mvq/r
charge and radius constant
therefore as mass and velocity increase, field has to increase in proportion

 

[freaking_out]

Originally posted by underthesun
I read something about mass dilation in particle accelerators, on some railgun experiment somewhere. Apparently they do, as I recall.

But taking into account that all the past relativity questions always had to talk about relativity in the question itself, this does not seem to be a relativity question. Hence, it is unlikely that relativity needs to be taken into account.

wishful thinkingl, wishful thinking. I feel a disturbance in the force.

so u didn't talk abt. relativity like me??

 

[ND]

I'd think they wanted relativity, otherwise why would they say 'near the speed of light'? They'd just say 'at a high speed'.

 

[ghoolz]

It didnt anything about the q B v V or anything like that.

I did shit on a bit at first then realised that it wanted to know what would happen when it reached near the speed of light.

It wanted the mass dilation and E=mc^2 equations and to show that as the velocity increased so did the mass thus requiring greater amounts of energy and then that energy would be converted into more mass requiring even more energy etc thus it would require an infinite amount of energy to accelerate it and this would be impossible.

Ahter the exam we saw our teacher and he said that it was the only real tough question in it but if you talked about mass dilation it would be ok. I didnt write alot about the infinite amount of energy required because I didnt realise until after. But i did write hopefully enough for most marks.

How many marks was it worth? 4?

 

[tooheyz]

Originally posted by B.Rabbit
I had NO CLUE...

me either dont worry... hopefully i get ONE mark for my crapping.. LOL

 

[walla]

Originally posted by ghoolz
It didnt anything about the q B v V or anything like that.

nor did it talk about mass dilation....but it did talk about magnetic fields so clearly you need to talk about the effect of the magnetic field on a charged particle, namely F=qvbsin...
also saying "accelerating it past the speed of light is impossible because it requires infinite energy" does not really answer the question which asked what changes needed to be made to the magnetic field to accelerate to a velocity near that of light

 

[Constip8edSkunk]

i think you need to equate qvb with mv^2/r (since @=90)
then sub m with the mass dilation eqn, ie the lorentz gamma factor, say which value is constant, say which value is variable and establish relationship between the B and other variables, ie v, describe what happens when v->c

 

[juber]

Hmm this question was interesting.

See like this is my approach...

The first formula I used was mass dilation and how as the velocity increases, the mass increases. This is the most important part of the question as far as I can see. If you didn't put that part in, I would doubt that you got the focus of the question (this is how I see it unless someone can convince me otherwise).

So i reckon you needed to put in the mass dilation formula as the basis to get your marks.

Where this then gets a bit iffy is when people try to relate other formulas to it.

Considering that this was a common question to all topics, they would not require anyone to even know what a particle accelerator was besides the fact that it speeds electrons close to the speed of light (as the question states)....

All the stuff about MV^2 / r would require a little bit more knowledge as it came in quanta to quarks. I dont therefore believe that such a relationship is necessary. Instead of doing this part of the question in my answer, I merely said that sychrotrons require constant acceleration to stay in phase with the AC current of the acclerator.

Peronally, i put that in order to maintain a constant accelleration, the force on the magnetic field would then need to be increased, and then related F = MA whereby in order to keep A the same whilst M increases, you need to increase F. Had I been in the right frame of mind I would have taken this a bit further to say F = QVB to relate how the increase in the magnetic field would increase the force, howevor I kinda assumed this a given / obvious therefore it went without saying.

Please, pull apart what I said, cos Id like to know if people think that my thinking is logic or not.

 

[walla]

f=mv^2/r has absolutely nothing to do with quanta to quarks
its the centripetal force straight out of core topic 1, space

(core 1 section 2 to be exact)

whatsmore its vital because it demonstrates that you need to increase the magnetic field as you accelerate it, proportional to the electron's velocity

as i showed above, B=mvq/r, and you should explain that two increasing quantities (mass and velocity) mean the field needs to be increased proportional to both

none of those calculations or concepts are covered AT ALL in q2q

 

[Bannanafish]

but as i've said earlier the particles in synchrotons don't travel in circular orbits, so centripetal force doesn't apply

what juber explained seems like the ideal answer to me, as long as you elaborated

 

[juber]

Originally posted by walla
f=mv^2/r has absolutely nothing to do with quanta to quarks
its the centripetal force straight out of core topic 1, space

(core 1 section 2 to be exact)

whatsmore its vital because it demonstrates that you need to increase the magnetic field as you accelerate it, proportional to the electron's velocity

as i showed above, B=mvq/r, and you should explain that two increasing quantities (mass and velocity) mean the field needs to be increased proportional to both

none of those calculations or concepts are covered AT ALL in q2q

Yeah, i appreciate that centripetal force is required to maintain a constant radius, but I dont believe that it is fair to expect non Q2Q students to know that this is required in a synchroton.

As I said, non Q2Q students wouldn't know how a synchroton accelerator works so how the fuck are they sposed to know that radius needs to be constant??

Is this not a fair call?

How could non Q2Q students know this information? It is not in the syllabus other than Q2Q therefore I dont think they will require knowledge on how the synchrotron works. Its just not going to be fair for those who didn't do Q2Q.

My proposition, is that as long as the student followed the following guidelines, they should get full marks:

1 - identified that mass increases as velocity increases
2 - identified that in order to maintain constant acceleration / velocity the magnetic field must increase in magnitude to couteract the changes in mass
3 - showed this concept mathematically using f=ma, f=qvb and the mass dilation formula.

The (mv^2 / r) equation IS relevant, BUT only if you are aware that the radius must be kept constant in synchrtotons. This is not part of what the question was aiming to test as of course this is something that exists in Quanta to Quarks and NOT the core in which this question was situated.

 

[dnt stop runnin]

i do quanta to quarks but i honestly dont believe we would have had an advantage since it was already telling u what the accelrator thing does and wat it is used for,,,,,,,i didnt even read up or learn about the particle accelators in the quanta section......but i was still able to answer the quesion which i think i had done right........but the question itself had already stated everything u needed to know....so yeh........but thats my opinion, i understand if others disagree

 

[Mr.Moonlight]

i wonder what the markers are really looking for, i hope it's about mass dilation, coz that's what i wrote

 

[dnt stop runnin]

my teacher said that they wanna c qvb=/MVsqaured/r.........this explains the whole answer

 

[juber]

Originally posted by dnt stop runnin
my teacher said that they wanna c qvb=/MVsqaured/r.........this explains the whole answer

well see i disagree with the mv^2/r part.

Like can someone clear up with me this one thing. People relate the mv^2/r part cos in the syncrotron the radius must be kept constant, and therefore due to the increasing mass, the force must change as per qvb?? Like this is the right relationship is it not?

See cos whilst I agree that this is correct, and would earn you brownie / tech head points, I dont believe that the markers can honestly include it into the marking guidelines as in order to aknowledge that this relationship exists, you would need to know that r needs to be kept constant in a synchroton - and this is not what the question was asking. Its not something that people would be expected to know as you would need to be able to do this question with no prior knowledge to synchrotrons.

Because you were expected to have no prior knowledge to synchrotrons, the only concept you needed to deduce is that as mass increases, the magnetic field is needed to increase.

Does anyone agree with me?

Cos like that mv^2 / r stuff requires you to know about synchrotrons, but we arent expected to in context to the core, so its irrelevant to at least the question

 

[juber]

Ok, so please, the following working explains the MV^2/r formula in application to this situation right?

But to refine once more what im saying, using this formula relies on the concept of R being constant which I am saying we cannot be expected to know.

Do you get me?

 

[helper]

The question told you the radius was constant

 

[juber]

Originally posted by helper
The question told you the radius was constant

Ohhh Did it really???

FUCK!

If only we could have a copy of the exam afterwards. then perhaps I could know before I went to all that trouble of explaining this through a diagram!

 

[helper]

"In a particle accelerator called a synchrotron magnetic fields are used to control the motion of an electron so that it follows a circular path of fixed radius"

 

[juber]

while your at it, how many marks was it worth?