OCR Physics G485 - June 2013 Unit 5 (OFFICIAL THREAD)

I am feeling cautiously optimistic about this exam. Just marked my attempt at the Jan 2013 paper, got 86/100 without notes so pretty happy! Couple of mistakes I made, I wrote them and thought 'actually it might be this' *marks paper* '**** it was.' So much for first instincts always being best. 4 and 5 mark questions on PET scans and CT scans, wrote too much for PET and not enough for CT :s-smilie:

Only problem was it took me about 3 hours. Probably would've been better if I'd been doing it in exam conditions, had the telly on and had to stop for dinner halfway through.

The resources on this thread have been fantastic, really helpful. For the first time before a physics exam I actually feel like I understand and remember everything, just need to sort out the silly mistakes. I need 130UMS in this exam to get an A overall because I stupidly didn't think about retaking G484, by the time I'd realised how far I was still off an A it was past the deadline for resits and I would've had to pay at least double :s-smilie:

Reply 585

Better

OP

About to do Jan 2013 Today, was going to do it earlier but err was focusing on Chemistry.

Please can anyone Clarify; It is to do with the Formation of Red-Giants. Any Answers would be appreciated.

Both Sets of Notes say that to form a Red Giant or Red Super Giant it is

Core He Fusion --> Carbon and Oxygen (Core Helium Burning) ----------> Red Giant / Red Super Giant

My Reasoning: Basically a larger star of 8-10 Solar Masses will have more mass and hence surely it will require the Core Fusion of heavier elements to form a RED SUPER GIANT. I.e. a Larger radiation Pressure, or does this not matter because there are more Fusion Reactions of He Fusion per second? I.e. more Fusions per unit mass? And hence more radiation pressure per Unit mass?

Then I don't understand the relevance of Fe (Iron). Is the Fusion of Iron what cores the Supernova or is it the Contraction into a Neutron Star which causes a supernova?

"3. Fusion can go all the way up to iron, beyond this is energetically unfavourable and so the star explodes in a supernova, becoming a neutron star or a black hole."

VS

"-When the core runs out of fuel it starts to contract, forming a white dwarf core.-If the star is massive enough and the core is about 1.4 times the mass of the sun, electron degeneracy pressure cannot stop the core from contracting.
-Electrons get squashed into nuclei of atoms and combine with protons to form neutrons and neutrinos.
-The core collapses to form a neutron star, which the outer layers fall onto
-Once the outer layers hit the surface they rebound, setting up shockwaves which rip the star apart, causing a supernova."

(edited 10 years ago)

Reply 586

paddyroddy

The outer layers contract and cause a shockwave as they hit the solid neutron core. That iw what causes the supernova

Reply 587

Tobias2

Original post by Rhodopsin94

Ermm...don't have my book to hand sorry, but I think I remember it being in the whole 'eV = hf' section and electrons needing KEmax to leave the cathode or something...not really making much sense probably because I can't remember specifics, but I'll have a look at some point if you want.

aaah think I get the basics of it. Thanks again!

Reply 588

101101

Are there any derivations or experiments we need to learn?

Reply 589

Picture~Perfect

19

Original post by 101101

Are there any derivations or experiments we need to learn?

Not that I'm aware of.

Reply 590

Better

OP

Original post by GeorgeL3

I've made some notes on the specification for this exam, I've tried to include everything I can using the terminology direct from the marks schemes etc. If anyone finds any errors please could you point them out to me? Thanks.

Original post by browb003

Definitely the circular motion topic and it'll probably be a good idea just to review resonance (just for confidence on the topic)

You two are the very best I know at Physics.

Please can you both provide advice on what I should do now -

Phyiscs 5 - I've finished all the Papers and 3 of them were 86-90% under timed conditions.
Physics 4 - I am not sure how to prepare as I've done all the papers before except Jan 2013 again so I don't really feel its a test of my skills. I've re-done 3 so far.

Should I go through all the Legacy Questions / End of Module Questions that I haven't done first?

I really want to do everything to get an A/A* in Physics, following your advice has really helped me this month; I don't know how I got good so fast - so anything would help.

(edited 10 years ago)

Reply 591

Just failed my chemistry exam, anyways now I can concentrate fully on G485 and chemistry unit 5 and C3.

Got a question:
In the mark scheme for photoelectric effect it says:

Where an orbital electron is ejected from the atom

And for Compton scattering, in a different paper, the mark scheme it says:

Incoming X-ray photon collides with an electron within the atom and the electron is ejected.

So are they saying that Compton scattering is the same thing as photoelectric effect?

(edited 10 years ago)

Reply 592

username807367

Original post by Namod

Just failed my chemistry exam, anyways now I can concentrate fully on G485 and chemistry unit 5 and C3.

Got a question:
In the mark scheme for photoelectric effect it says:

And for Compton scattering, in a different paper, the mark scheme it says:

So are they saying that Compton scattering is the same thing as photoelectric effect?

In photoelectric effect, a photon is absorbed and the electron ejected, Compton scattering the electron is ejected (but I don't really know why) and the photon rebounds through angle theta and the frequency changes. I think. Probably more to it than that but that's all I can remember.

Posted from TSR Mobile

Reply 593

Original post by GeorgeL3

I've made some notes on the specification for this exam, I've tried to include everything I can using the terminology direct from the marks schemes etc. If anyone finds any errors please could you point them out to me? Thanks.

Where you got this information from:

Photoelectric effect: Photon uses all of its energy to eject an electron from an atom. <0.1 MeV
Compton Scattering: Photon loses some of its energy to remove an electron. Longer wavelength X-ray (hence lower energy) & electron are scattered in different directions to conserve momentum. 0.5-5 MeV
Pair Production: Photon travelling through electric field of a nucleus suddenly forms an electron/positron pair. >1.02 MeV

If you found it from a text book, I'm going to stick with the past paper answers for it.

Reply 594

Original post by hrbrox

In photoelectric effect, a photon is absorbed and the electron ejected, Compton scattering the electron is ejected (but I don't really know why) and the photon rebounds through angle theta and the frequency changes. I think. Probably more to it than that but that's all I can remember.

Posted from TSR Mobile

ok thanks I will just learn what the mark scheme has said.

Reply 595

GeorgeL3

5

Original post by Better

You two are the very best I know at Physics.

Please can you both provide advice on what I should do now -

Phyiscs 5 - I've finished all the Papers and 3 of them were 86-90% under timed conditions.
Physics 4 - I am not sure how to prepare as I've done all the papers before except Jan 2013 again so I don't really feel its a test of my skills. I've re-done 3 so far.

Should I go through all the Legacy Questions / End of Module Questions that I haven't done first?

I really want to do everything to get an A/A* in Physics, following your advice has really helped me this month; I don't know how I got good so fast - so anything would help.

I'm planning on not doing much physics until after Monday since I've got 4 maths exams before then. Then up until the physics exam I was planning on redoing some of the papers because it doesn't matter so much if you've done them before, half the questions are the same from exam to exam anyway.
I would advise making some notes on the specification or something if you're at a loss, I find it helps to make sure you haven't missed anything out.
Another helpful thing maybe would be to prepare model answers to common questions that always come up.
For unit 4 definitely redo the papers you haven't done since the January exam, this is definitely the most helpful thing that helps me revise.
If you have time then go through the older material first but otherwise just go straight for the past papers.

Also, you say we're the best at physics you know but paddyroddy is here now :wink:

I challenge you to find a question he can't answer!

Reply 596

GeorgeL3

5

Original post by Namod

Where you got this information from:

If you found it from a text book, I'm going to stick with the past paper answers for it.

The mark scheme answer says:

12 Jan mark scheme

Compton (scattering)
Incoming photon collides with an electron, the electron is ejected
and the photon is scattered / has lower energy

Reply 597

Jamie T

So I'm starting my full on revision for this exam tomorrow... and this thread is starting to scare me.

Reply 598

Thank you everyone.

(edited 10 years ago)

Reply 599

Better

OP