Competition - post a photo you've taken of nature >>

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

Scroll to see replies

Mutleybm1996

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

R=\frac{0.61\lambda}{NA}

but you can take this as the resolving power is just

R=\frac{\lambda}{2}

for this, so you would use

Unparseable latex formula:

250\times10^-^9m

as it's half the wavelength of the light.
Non Latex in spoiler.

Spoiler

Do we need to know those formulae?

Posted from TSR Mobile

Reply 41

Cerdic

Original post by Mutleybm1996

Do we need to know those formulae?

Posted from TSR Mobile

No idea, it seems quite obscure for G495 tbh. Knowing the simplification ie

R=\frac{\lambda}{2NA}

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.

Reply 42

Mutleybm1996

Original post by Cerdic

No idea, it seems quite obscure for G495 tbh. Knowing the simplification ie

R=\frac{\lambda}{2NA}

What's

R=\frac{\lambda}{2NA}

?? What's R? N? A?

Posted from TSR Mobile

Reply 43

Cerdic

Original post by Mutleybm1996

What's

R=\frac{\lambda}{2NA}

?? What's R? N? A?

Posted from TSR Mobile

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

NA=n\sin\theta

where n is the refractive index of the material that the light is travelling through and

\theta

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.

Reply 44

Rhetorical Hips

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).

Reply 45

Mars256

What are peoples suggestions to revise for section C?

Reply 46

Robbo54

Anyone have any hard electromagnetism questions? I find magnets really hard :frown:

Reply 47

Cerdic

Original post by Robbo54

Anyone have any hard electromagnetism questions? I find magnets really hard :frown:

Are you having problems with the calculations or getting the explanations right?

Reply 48

Robbo54

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.

Reply 49

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

Reply 50

Tibbz2

Original post by RoryV

Of course it depends on how the paper is.

But 80-85 is a safe bet.

Reply 51

Cerdic

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

Average is 84 for 138 UMS

Reply 52

Mutleybm1996

(Wrong thread)

Posted from TSR Mobile

Reply 53

STATER

Original post by Robbo54

Anyone have any hard electromagnetism questions? I find magnets really hard :frown:

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).

Reply 54

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????

Reply 55

Nikeshp79

Original post by RoryV

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

Reply 56

RoryV

Original post by Nikeshp79

Yep, silly me, thankyou :smile:

I was doing V/x, rather than dV/dx

Reply 57

Nikeshp79

Original post by RoryV

Yep, silly me, thankyou :smile:

I was doing V/x, rather than dV/dx

You're welcome, everyone makes silly mistakes :tongue:

Some more than others (I usually make silly mistakes, and is why I bought the silver CASIO calculator for maths hehe)

Reply 58

Rhetorical Hips

Original post by Nikeshp79

You're welcome, everyone makes silly mistakes :tongue:

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 😄

Posted from TSR Mobile

Reply 59

Nikeshp79

Original post by Rhetorical Hips

The one that can do definite integrals a for you? I got that for maths last year as well 😄

Posted from TSR Mobile

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!