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

1. (Original post by Cerdic)
Yeah you can assume 5pm is the wavelength or you can use your answer, a mark scheme will take both.

The smallest detail that can be resolved by a microscope using normal light is

but you can take this as the resolving power is just for this, so you would use as it's half the wavelength of the light.
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Resolving power:
R=0.61*lambda / NA

Can assume:
R=lambda/2

So would use:
250*10^-9 m
Do we need to know those formulae?

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2. (Original post by Mutleybm1996)
Do we need to know those formulae?

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No idea, it seems quite obscure for G495 tbh. Knowing the simplification ie can't hurt, but I doubt a question like that will come up, although to be fair I haven't read the advanced notice article, it just seems a bit far off. If it was in G491 then you'll have to as it's synoptic, but it's been two years now since I did that.
3. (Original post by Cerdic)
No idea, it seems quite obscure for G495 tbh. Knowing the simplification ie can't hurt, but I doubt a question like that will come up, although to be fair I haven't read the advanced notice article, it just seems a bit far off. If it was in G491 then you'll have to as it's synoptic, but it's been two years now since I did that.
What's ?? What's R? N? A?

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4. (Original post by Mutleybm1996)
What's ?? What's R? N? A?

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R is the resolution, so the smallest resolvable detail. NA you shouldn't worry about (I don't think), but as a matter of interest it stands for numerical aperture and is calculated by where n is the refractive index of the material that the light is travelling through and us the angle of the light to the edge of the lens. As I said, do not worry about that! Just remember that the resolution is roughly equal to half the wavelength of the light.
5. Anyone else find it difficult to understand the electron energy levels section? It's not so much I don't understand it, I just don't know what they want us to know. Do we need to know the derivations of certain formulae? If so, they haven't really mentioned anything in the specification (we all know how useless the OCR specs are anyway - I doubt they bother referring to it whilst writing exam papers, at least).
6. What are peoples suggestions to revise for section C?
7. Anyone have any hard electromagnetism questions? I find magnets really hard
8. (Original post by Robbo54)
Anyone have any hard electromagnetism questions? I find magnets really hard
Are you having problems with the calculations or getting the explanations right?
9. (Original post by Cerdic)
Are you having problems with the calculations or getting the explanations right?
Both really, I can do the basic Farday's law and draw the graphs of flux and emf, but the questions on eddy currents/motors usually cause me concern.
10. I need an A* in physics to get into Uni. Based on my coursework raw marks, and how many UMS i think i'll have got in G494, i reckon i need 138UMS in G495.
Anyone know roughly what sort of raw mark 138UMS would translate to? I was thinking maybe around 80/100 but not too sure
11. (Original post by RoryV)
I need an A* in physics to get into Uni. Based on my coursework raw marks, and how many UMS i think i'll have got in G494, i reckon i need 138UMS in G495.
Anyone know roughly what sort of raw mark 138UMS would translate to? I was thinking maybe around 80/100 but not too sure
Of course it depends on how the paper is.

But 80-85 is a safe bet.
12. (Original post by Robbo54)
Both really, I can do the basic Farday's law and draw the graphs of flux and emf, but the questions on eddy currents/motors usually cause me concern.
Ah I can't really help you there, it's always been my hardest bit as well. Do you understand the markscheme when you mark your answers?

(Original post by RoryV)
I need an A* in physics to get into Uni. Based on my coursework raw marks, and how many UMS i think i'll have got in G494, i reckon i need 138UMS in G495.
Anyone know roughly what sort of raw mark 138UMS would translate to? I was thinking maybe around 80/100 but not too sure
Average is 84 for 138 UMS

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14. (Original post by Robbo54)
Anyone have any hard electromagnetism questions? I find magnets really hard
Do you have any particular questions? I think I have a decent understanding of magnetism, though haven't touched G495 for 3 weeks or so now, so it will be helpful revision for me too (seeing If I can explain it properly).
15. Help please. June 2010 G495 Q2 part c.
My thought process was that field strength at first equipotential is 195k/0.005 = 3.9 x 10^7, and the field strength will get stronger, the closer you go to the surface, so chose 4x10^7 as the answer.
The mark scheme says the answer is 1x10^6????
16. (Original post by RoryV)
Help please. June 2010 G495 Q2 part c.
My thought process was that field strength at first equipotential is 195k/0.005 = 3.9 x 10^7, and the field strength will get stronger, the closer you go to the surface, so chose 4x10^7 as the answer.
The mark scheme says the answer is 1x10^6????
You use dV/dx (change in voltage/ change in distance)

If I remember that question correctly, the difference between the equipotentials is 5kV and the distance from the surface is 5mm.

so 5000/0.005 = 1x10^6 V m^-1
17. (Original post by Nikeshp79)
You use dV/dx (change in voltage/ change in distance)

If I remember that question correctly, the difference between the equipotentials is 5kV and the distance from the surface is 5mm.

so 5000/0.005 = 1x10^6 V m^-1
Yep, silly me, thankyou I was doing V/x, rather than dV/dx
18. (Original post by RoryV)
Yep, silly me, thankyou I was doing V/x, rather than dV/dx
You're welcome, everyone makes silly mistakes Some more than others (I usually make silly mistakes, and is why I bought the silver CASIO calculator for maths hehe)
19. (Original post by Nikeshp79)
You're welcome, everyone makes silly mistakes Some more than others (I usually make silly mistakes, and is why I bought the silver CASIO calculator for maths hehe)
The one that can do definite integrals a for you? I got that for maths last year as well 😄

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20. (Original post by Rhetorical Hips)
The one that can do definite integrals a for you? I got that for maths last year as well 😄

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Yeah it may just possibly get me an A* >_< But I can say with confidence that, if I get an A, it has definitely helped me move my extremely low B up to that!

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