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# OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012

Physics exam discussion - share revision tips in preparation for GCSE, A Level and other physics exams and discuss how they went afterwards.

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1. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
AHHHHH

"describe briefly one experiment to investigate the size of the nucleus of the atoms = Include a description of the properties of incident radiation which makes it suitable for the experiment"

I can't do this = it make no sense

Any help / links would be soooo appreciated
2. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
Guys can you help me?

4B. I would do it as 120+120+ 1/120. However this is wrong.

Markscheme says this:
Cparallel = 240 (uF)
CT = (240 x 120)/(240 +120) or CT = (240-1 + 120-1)-1
total capacitance = 80 (uF)

How? can someone explain this to me?
3. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
(Original post by Moiraclaire)
AHHHHH

"describe briefly one experiment to investigate the size of the nucleus of the atoms = Include a description of the properties of incident radiation which makes it suitable for the experiment"

I can't do this = it make no sense

Any help / links would be soooo appreciated
wouldn't you talk bout The alpha particle scattering experinment?
4. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
(Original post by Brap4k22DivideBy2)
Guys can you help me?

4B. I would do it as 120+120+ 1/120. However this is wrong.

Markscheme says this:
Cparallel = 240 (uF)
CT = (240 x 120)/(240 +120) or CT = (240-1 + 120-1)-1
total capacitance = 80 (uF)

How? can someone explain this to me?
capacitors in series is (1/C1 + 1/C2) capacitors in parralell (C1+C2)
in this case you have (1/120) + ( 1/(120+120) ) = 1/80....therfore Ctotal= 80/1
5. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
(Original post by stunnaman)
wouldn't you talk bout The alpha particle scattering experinment?
apparently so ! It was a question on the spec paper, I don't understand the links between points in the mark scheme and obviously I can read the textbook, but I wanna know how it is applied to the question. There is no 'higher band model student answers' for the spec of G485 ahhh
6. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
(Original post by Moiraclaire)
apparently so ! It was a question on the spec paper, I don't understand the links between points in the mark scheme and obviously I can read the textbook, but I wanna know how it is applied to the question. There is no 'higher band model student answers' for the spec of G485 ahhh
I've done the Specimen paper and the answers they were looking for for that question were completely unrelated to anything I've ever seen asked.

Also, there are no model answers because they don't mark you in the same way that they do for English... if you write down 8 points that they're looking for in an 8 mark question you'll usually get 8 marks
7. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
(Original post by Moiraclaire)
apparently so ! It was a question on the spec paper, I don't understand the links between points in the mark scheme and obviously I can read the textbook, but I wanna know how it is applied to the question. There is no 'higher band model student answers' for the spec of G485 ahhh
I am not really sure but if i came across this question id probably describe the basic setup of the experiment
and then talk about how the a-particle energy shouldnt be so great so the nucleaus of the atom could deflecct and possibly more chance of head on collisions. The results for head on collisons involving the closest distance of approach allow an estimate of the radius of nucleus to be done. if the energy is too great it will just pass through atom... i have a feeling maybe thats what theyre after?
8. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
(Original post by wibletg)
I've done the Specimen paper and the answers they were looking for for that question were completely unrelated to anything I've ever seen asked.

Also, there are no model answers because they don't mark you in the same way that they do for English... if you write down 8 points that they're looking for in an 8 mark question you'll usually get 8 marks
when I say model answers, I mean these things

There are these type of things for G482 and G484 but not G485.
9. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
(Original post by stunnaman)
capacitors in series is (1/C1 + 1/C2) capacitors in parralell (C1+C2)
in this case you have (1/120) + ( 1/(120+120) ) = 1/80....therfore Ctotal= 80/1
Ok, I've got it. Adding the two parallel capacitors will create a total for that part of the circuit, so technically a single capacitor lets say. Then Ctotal would be 1/c1+ 1/c2. So 1/120+ 1/240. Yes Thanks! So simple...Why am I not getting this?
10. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
Only 3 Weeks to go!!
We could start doing model answers. Someone will come up with a question and the rest of us can have a go at answering it.
I'll start it off

Describe one way in which X-Rays interact with matter (4 marks)
Hint:
Spoiler:
Show
choose from the Compton Effect, Pair Production and the Photoelectric Effect
11. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
(Original post by magdaplaysbass)
Only 3 Weeks to go!!
We could start doing model answers. Someone will come up with a question and the rest of us can have a go at answering it.
I'll start it off

Describe one way in which X-Rays interact with matter (4 marks)
Hint:
Spoiler:
Show
choose from the Compton Effect, Pair Production and the Photoelectric Effect
Photoelectric effect.

Each x-ray photon interacts with one electron. If the x-ray photon has a frequency above the threshold frequency of the matter then it will have sufficient energy to remove an electron from the surface of the matter and the matter will be ionised. If there is excess energy it will be converted to kinetic energy for the electron.

EDIT: For low energy X-Ray photons.
Last edited by wibletg; 21-05-2012 at 19:31.
12. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
(Original post by magdaplaysbass)
Only 3 Weeks to go!!
We could start doing model answers. Someone will come up with a question and the rest of us can have a go at answering it.
I'll start it off

Describe one way in which X-Rays interact with matter (4 marks)
Hint:
Spoiler:
Show
choose from the Compton Effect, Pair Production and the Photoelectric Effect
Compton Effect

• Incoming X-ray photon collides with an orbital electron.
• This is an inelastic collision, and the photon transfers energy to the electron.
• The electron is ejected and the photon is scattered (has lower energy).
• This requires a higher voltage system that is required for the photoelectric effect.

(I'm not sure if one way is enough to get 4 marks? In the Jan 2012 paper, two ways had to be explained to give four marks...)

Anyway, let's continue...

Describe the formation of a star, such as the Sun, from interstellar gas and dust.

EDIT: Oh yeah. [6 marks]
13. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
(Original post by Beth1234)
Compton Effect

• Incoming X-ray photon collides with an orbital electron.
• This is an inelastic collision, and the photon transfers energy to the electron.
• The electron is ejected and the photon is scattered (has lower energy).
• This requires a higher voltage system that is required for the photoelectric effect.

(I'm not sure if one way is enough to get 4 marks? In the Jan 2012 paper, two ways had to be explained to give four marks...)

Anyway, let's continue...

Describe the formation of a star, such as the Sun, from interstellar gas and dust.

EDIT: Oh yeah. [6 marks]
Hi - just googled this but isn't Compton scattering an elastic collision?

I might be wrong
14. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
OMG I'm so worried for this exam. Teacher gave me some capacitor questions from a 2009 paper and I have no idea if I've done them right. Does anyone have Jan or June 2009 paper with the mark scheme?
15. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
Is this the lifecycle of the Sun?

• The material of the star is acted upon by two forces, Gravity and Nuclear Reaction Forces.
• Hydrogen in converted into Helium.
• Rate of fusion eventually decreases in the core of the Sun as the Hydrogen is used up and converted to Helium.
• The core contracts.
• The loss of potential energy ion contraction results in increase in kinetic energy and so the temperature and pressure in the core increases.
• Helium nuclei fuse to make heavier elements.
• Radiation pressure is now greater and so outer parts of star expand.
• There's greater luminocity because of an increased surface area and the surface temperature is less due to increase in potential energy - Red Giant.
• As fusion stops the stability of the Sun decreases. The outer layer is lost.
• The remains of the star collapse under its own gravity and becomes a white dwarf.
16. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
(Original post by wibletg)
Hi - just googled this but isn't Compton scattering an elastic collision?

I might be wrong
Just had a look through Google, and it seems that it's an elastic collision, so total kinetic energy of photon and electron is conserved. But it's an example of inelastic scattering (when the incoming particle, that is, the photon, leaes with a different energy that it began with) - I'm guessing that's what the book I got this from meant...

So, in short, you're right!
17. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
(Original post by Beth1234)
Describe the formation of a star, such as the Sun, from interstellar gas and dust.

EDIT: Oh yeah. [6 marks]
• Regions of dust and gas with different densities
• The regions with higher densities have more gravitational pull towards them, so over time they become even more dense.
• the density increases even more to form a stellar nebula
• density continuous to increase, resulting in more collisions between atoms, so PE decreases and KE & temperature both increase.
• the process is repeated until a protostar is formed (a massive core that glows)
• the protostar attracts even more material and becomes large enough to emit light
• the core has a high density, pressure and temperature; allowing for the fusion of hydrogen and helium

(Original post by Mr Maths)
OMG I'm so worried for this exam. Teacher gave me some capacitor questions from a 2009 paper and I have no idea if I've done them right. Does anyone have Jan or June 2009 paper with the mark scheme?
they don't have then 2009 G485 papers on the OCR website, but you could try http://www.xtremepapers.com/
What's the question? One of us on here might be able to help you out

Describe the use of capacitors in Flash Photography, Lasers used in nuclear fusion and as a back-up power supply for computers (6 marks) 2 marks for each application
18. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
I should have started using this website ages back, this thread has helped me loads.
19. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
A random thought when I was revising today...

If the Hubble constant is a constant, and 1/hubble constant=age of the universe, wouldn't it imply that the age of the universe doesn't change?
20. Re: OCR Physics A - G485: Fields, Particles & Frontiers of Physics - June 2012
(Original post by whotosee)
A random thought when I was revising today...

If the Hubble constant is a constant, and 1/hubble constant=age of the universe, wouldn't it imply that the age of the universe doesn't change?
Hubble's constant isn't strictly a 'constant' - it changes depending on the scientific data available.

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