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# 6 mark phy6 question, can you get all marks? watch

1. Describe a linear accelerator. e.g a linac
6 marks no clarity marks.

Also, describe a van de graff fully - 5 marks again, no clarity

past paper questions.
2. (Original post by nas7232)
Describe a linear accelerator. e.g a linac
6 marks no clarity marks.

Also, describe a van de graff fully - 5 marks again, no clarity

past paper questions.
Is this edexcel phy6?
3. Im assuming you means discribe how linac works?

Ill just bullet point,

Particle travels through a series of cylindrical tubes. Each on which are connected to the opposite polarity of an alternating current, switching with a constant frequancy.
When particle reaches end on tube, power supply switches.
Particle is mutually attracted to the adjacent tube, and repeled from current tube.
This electrostatic force accelarates the particle.
As the particle accelerates, its speed increases through each tube. The length of the tube is increased to account for the increasing distance travelled, so attraction takes place at correct points.
4. (Original post by RMIM)
Is this edexcel phy6?
Yep
5. (Original post by SinghFello)
Im assuming you means discribe how linac works?

Ill just bullet point,

Particle travels through a series of cylindrical tubes. Each on which are connected to the opposite polarity of an alternating current, switching with a constant frequancy.
When particle reaches end on tube, power supply switches.
Particle is mutually attracted to the adjacent tube, and repeled from current tube.
This electrostatic force accelarates the particle.
As the particle accelerates, its speed increases through each tube. The length of the tube is increased to account for the increasing distance travelled, so attraction takes place at correct points.
Yeah, that's some good stuff, but you are missing soem vital points.

- Ion spends equal time in each tube
Then the obvious critisms of the linac - i.e has a finite left because of the earth's curvature.

I'm good on these questions like cyclotron synchocyclotron e.t.c

but can anyone do the second one? My teacher failed to teach us that bit

Also, anyone know the differences between a
spark
bubble
cloud chamber?

Cheers
6. Spark chambers are really weird. Its like a loads of "slices" of metal conductors piled on top of each other. There is a huge p.d. between them, which helps create the spark. The spark occurs because the source ionised the air, releasing loads of free electrons, which cause a current to pass between the potentials.
I still dont understand the point of it though.
All I know is when you have a magnetic field perpendicular to conductors, the spark moves tries to move in a cercular path. This path gives information about the particles charge(direction it travels), and also the mass (by the radius of its circular path; something to do with Bqv=mv^2/r).
Oh, and also some of the advantages of it over a bubble/cloud camber is that you can use a computer to monitor the sparks (since its a electrical), and you can also view the spark in 3 dimensions.
Maybe I do remember something!

A bubble chambers is a chamber, which is filled with liquid nitrogen. When a source is placed near by, it ionises the ions in the Nitrogen. Bubbles form around the paths, which are visable.
Cloud chambers use a thin layer of ice, and an alcohol, which creates the "cloud".
When a source passes, it ionises the air again. This ionisation displaces the "clouds", molecules, creating a clear path.
I was told its similar to the jets of smoke that aircrafts leave in the sky, except the other way around.
7. You may need to find out how frequantly the frequancy of the cylotron needs to be switched, to accelarate the particle.
I cant remember how to do this :/
8. you use an equation which i cant find now because i left my notes lying about somewhere

i try to recall it for you.. its like

r = vt
t= r/v

F=BQv
mv²/r = Bev

it's derrived from these equations.
9. hmm...Ill have a go at deriving it from that;

vr=w
so,
mv^2/w=Be

2pi/T=w so,
mv^2/(2pi/t)=Be
therefor mv^2/2pi 1/t = be
but 1/t equals f, so mv^2/2pi f = be

so mv^2 = 2pi f B e

that must mean that
f= mv^2/2pi Be

is that right ? it looks wrong
10. [QUOTE=nas7232]Yeah, that's some good stuff, but you are missing soem vital points.

- Ion spends equal time in each tube
he already said it in another way
As the tubes get longer in the linac, the plates must get further apart
Then the obvious critisms of the linac - i.e has a finite left because of the earth's curvature.

I'm good on these questions like cyclotron synchocyclotron e.t.c

Cheers
I don't think that theses are needed from us that the plates get further or whatever, I've never read that before and also they have never put it in the markscheme
my teacher asked a dude who came here from edexcel about what do they mean with clearity of your answer he told her that we give the paper to a history teacher if he got what is written down then the mark for the clearity is taken
11. (Original post by habosh)
I don't think that theses are needed from us that the plates get further or whatever, I've never read that before and also they have never put it in the markscheme
my teacher asked a dude who came here from edexcel about what do they mean with clearity of your answer he told her that we give the paper to a history teacher if he got what is written down then the mark for the clearity is taken
it's in the june 2004 markscheme. Plus the question asked to describe a linac which means it shouldn't be soley described on how it operates but other factors of the linac too. The question is 1 my teacher made but a similiar 1 is on the june 2004 phy6 paper.

Best to just learn everything i suppose, but the new crappy papers have a specific number of lines to write on
12. (Original post by SinghFello)
hmm...Ill have a go at deriving it from that;

vr=w
so,
mv^2/w=Be

2pi/T=w so,
mv^2/(2pi/t)=Be
therefor mv^2/2pi 1/t = be
but 1/t equals f, so mv^2/2pi f = be

so mv^2 = 2pi f B e

that must mean that
f= mv^2/2pi Be

is that right ? it looks wrong
let me check

mv^2/r = BQv
mv/r = BQ
since e = Q in this case
v = Ber/m

t = r/v

so

1/f = πr/[Ber/m]
f = Be/πr

That's it
13. my try:

linear arrangement if loops alternately connected to positive and negative electrodes of an alternating potential difference
as the charged particle starts, the first loop generates an electric field and the particle accelerated towards it. when the particle is in the middle of the first loop, the polarity is switched and the electric field between the first and second loops accelerates the particle towards the 2nd loop.
further along the accelerator loops become more streched and further apart so that a constant frequency of alternating p.d. can be used.

btw I think you may be penalised or not gain marks for saying alternating current - there is no circuit and it is not relevant to argue the cylinders act as capacitors (leading to a slight current)
14. (Original post by mik1w)
my try:

linear arrangement if loops alternately connected to positive and negative electrodes of an alternating potential difference
as the charged particle starts, the first loop generates an electric field and the particle accelerated towards it. when the particle is in the middle of the first loop, the polarity is switched and the electric field between the first and second loops accelerates the particle towards the 2nd loop.
further along the accelerator loops become more streched and further apart so that a constant frequency of alternating p.d. can be used.

btw I think you may be penalised or not gain marks for saying alternating current - there is no circuit and it is not relevant to argue the cylinders act as capacitors (leading to a slight current)
you can say alternating current [it is encouraged] but you do get penalised bigtime for saying the tubes are plates. After all, it is an alternating current, but make sure you mention tubes, plates will lose 2 marks.
15. there is no current though? it is not a circuit, just a series of electrodes with insulation (air) between them, so the current will be zero! I wouldn't say that was alternating.

it is the alternating electric field due to alternating potential difference that causes the particle to acceelrate...?
16. it is in a linac, there is an a.c between the tubes.

If you have a good diagram of a linac you can see it in there, there is a good 1 in the physics for you book. Just to back up that, in the june 2004 ms. You get 1 mark for stating that there is an a.c between the tubes.
17. (Original post by nas7232)
it's in the june 2004 markscheme. Plus the question asked to describe a linac which means it shouldn't be soley described on how it operates but other factors of the linac too. The question is 1 my teacher made but a similiar 1 is on the june 2004 phy6 paper.

Best to just learn everything i suppose, but the new crappy papers have a specific number of lines to write on
they mean that you either write as the tube gets longer particle spends the same time
or the same senctence but as the plates get furthure apart,the slash means or either
18. Nah it is an ac (p.d. or current should be acceptable) and charged particles accelerate in the gap between the electrode tubes.
19. (Original post by mik1w)
there is no current though? it is not a circuit, just a series of electrodes with insulation (air) between them, so the current will be zero! I wouldn't say that was alternating.

it is the alternating electric field due to alternating potential difference that causes the particle to acceelrate...?
yeah there is an electric field due to the high potential difference between the electrodes
20. (Original post by habosh)
they mean that you either write as the tube gets longer particle spends the same time
or the same senctence but as the plates get furthure apart,the slash means or either
there is no slash, you get 2 seperate marks.

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