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# OCR PHYSICS B G495~ 18th June 2015 AM ~ A2 Physics watch

1. (Original post by falconinni)
You used pV=NkT, rearranging for N/V. You then had to convert cm^3 to m^3
2. Fairly happy with that - I nailed section C (I got 0.027m too!), section B and A were decent on the whole. Had no clue about the induction 4 marker but put something down so I'll hopefully pick up a mark or two there, also made a couple of silly errors on section A bit hopefully I've done enough overall - I need about 130UMS in this paper for an A* aproximately.
3. (Original post by falconinni)
You used pV=NkT, rearranging for N/V. You then had to convert cm^3 to m^3
Damn
I set V=1 and solved for N....
Grrrr
4. Oh so the answer was N/V? I thought it was just V
5. (Original post by Mutleybm1996)
Damn
I set V=1 and solved for N....
Grrrr
I think you are correct actually. Just had to convert to cm.
6. (Original post by STATER)
I think you are correct actually. Just had to convert to cm.
Whoops
Oh well
-1 mark there

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7. For induction I said that rotation causes an opposing current to be induced. Stopping rotation stopped this 'back emf' increasing net current.
8. (Original post by Mutleybm1996)
Damn
I set V=1 and solved for N....
Grrrr
Setting V to 1 should get the same answer
9. (Original post by STATER)
I can't remember :/
10. (Original post by STATER)
I think you are correct actually. Just had to convert to cm.
No I'm sure it was N/V, if they wanted you to say V=1 they would have included it when they told us the values of P and T etc.
11. (Original post by STATER)
For induction I said that rotation causes an opposing current to be induced. Stopping rotation stopped this 'back emf' increasing net current.
That sounds correct, definitely. I just couldn't think straight about it in the exam and so I only got the bit about an opposing current being created, which is annoying, so at least -2 marks there for me. Well done though, how did you find the whole paper?
12. (Original post by Lord-Febreeze)
No I'm sure it was N/V, if they wanted you to say V=1 they would have included it when they told us the values of P and T etc.
Its per cm^3 if I recall correctly which means v=1cm
13. (Original post by urz13)
That sounds correct, definitely. I just couldn't think straight about it in the exam and so I only got the bit about an opposing current being created, which is annoying, so at least -2 marks there for me. Well done though, how did you find the whole paper?
In general it was exactly what I wished for. All the extensive preparation payed off and there weren't many surprises.
14. (Original post by STATER)
Its per cm^3 if I recall correctly which means v=1cm
So I would need to convert to cm?
15. Harder or easier than 2014? I think section C was a bit trickier, induction was harder. Radiation was easy. Electric fields was non standard so a bit trickier. Maybe boundaries might fall by one mark or stay the same?
16. FML I dropped perhaps 6 marks in most of the paper but didn't see the double page spread at the end........
17. I got N to be 2.4x10^9 or something.

Anyone else get a resolution of 5.2x10^-7 and 30,000 lenses covering the eye?
18. Don't remember the question, something to do with a rotor in a stator where something increases (might have been potential difference but I'm not sure). It asks what happens to the speed of rotations? I put that although the force on the rotor will increase, the speed of rotations does not due to the fact that the question stated that the current remains the same and I figured this meant that the poles don't switch any quicker so it can't spin any faster... Does anyone agree/disagree? And does anyone actually remember the question properly?
19. (Original post by Minecraft27)
I got N to be 2.4x10^9 or something.

Anyone else get a resolution of 5.2x10^-7 and 30,000 lenses covering the eye?
Got the same resolution. Can't remember lenses exactly, but it wasn't far off that.
20. (Original post by Minecraft27)
I got N to be 2.4x10^9 or something.

Anyone else get a resolution of 5.2x10^-7 and 30,000 lenses covering the eye?
I got about 22000, did it assuming there were 36 lenses per square 100m^-6... might have been more if you used a circle. Got the same resolution.

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