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# OCR Physics B G495 Field and Particle Pictures June 21st 2011 Exam Thread watch

1. (Original post by Summerdays)
path difference = n xlambda (for constructive interference) Path difference = (0.5+n)lambda (for destructive interference.)

The second equation is definitely something they will ask us to derive but it comes from E= p^2/2m, lambda = h/p and lambda = 2d/n - like you said
thought id let you know im pretty certain youl be getting an A* if theres any justice in the world! also thanks for all your help :-)

oh and meridian, does it go directly through the centre of the earth or like via the circumference?
2. (Original post by Summerdays)
Anyone got some random physics questions (from g495) to ask me?
Why are we expected to know "estimates" for the radius of a Carbon-12 nucleus?
3. In the practise advanced notice article questions, one question is: For practical purposes, the BIPM suggests use of a Helium-Neon laser for establishing the length of a meter. The wavelength of the lasers, ?HeNe,, is accepted as being 632.99139822 nm. If an atomic clock based wave counter is used that is capable of counting individual waves, how many waves would pass in one second? (The device will only provide a whole number count.)

Caqn anyone answer this for me??
4. If anyone's done the January 2011 past paper could someone explain question 10.c) please.

Have no idea why the MS has made the ratio rise to the power 3.
5. (Original post by 41jms)
thought id let you know im pretty certain youl be getting an A* if theres any justice in the world! also thanks for all your help :-)

oh and meridian, does it go directly through the centre of the earth or like via the circumference?
I think so, it's not something that's really explained. What I do know is that the distance from the equator to the north/south pole is a quarter of the circumference

Also, thank you soooooo muh for the compliment. I need an A in physics to get into Imperial to study chemistry. I am a gappy
I always found OCR B physics to be ridiculous
6. (Original post by rggregrgr)
Why are we expected to know "estimates" for the radius of a Carbon-12 nucleus?
The radius of the nucleus of Carbon-12 is approximately the same as the radius of other nuclie. This is always around 10^-14 m, while the radius of the WHOLE atom is about 10^-10m
7. (Original post by ChicharitoH)
In the practise advanced notice article questions, one question is: For practical purposes, the BIPM suggests use of a Helium-Neon laser for establishing the length of a meter. The wavelength of the lasers, ?HeNe,, is accepted as being 632.99139822 nm. If an atomic clock based wave counter is used that is capable of counting individual waves, how many waves would pass in one second? (The device will only provide a whole number count.)

Caqn anyone answer this for me??
I too was a bit stuck on this question; it doesn't make any sense really Like REALLY doesn't make any sense.
8. (Original post by Summerdays)

Oblateness is basically an irregular sphere, in this case a sphere that bulges equatorially, and as consequence the north and south pole squash together. The reason, based on my understanding, for this is because when the earth is rotating the gravitational force from the centre of mass is greater - in order to provide a cetripetal force that causes the elements in the earth to rotate, the gravitational force must be greater than the force due to the pressure difference from the Earth's fluid mantle.
If the force due to gravity is larger at the equitorial plane than the force due to the pressure difference, why does it bulge at the equator?
I'm a little confused :P

http://www.johnbright.conwy.sch.uk/d.../G495Jun10.pdf

i dont get how the half lives is 4.
10. (Original post by Summerdays)
Th radius of the nucleus of Carbon-12 is approcimateloy the same as the radius of other nuclie. This is always around 10^-14 m, while the radius of the WHOLE atom i about 10^-10m
Thank you! I'll remember that now but I imagine it won't come up again tomorrow! Seems like one of those random facts OCR decide to pull out of their arse once and once only.
11. (Original post by Summerdays)
I too was a bit stuck on this question; it doesn't make any sense really Like REALLY doesn't make any sense.
Haha glad I'm not the only one lol I thought that that the waves that pass in one second is just the frequency so you would use v = f(lambda) and then v/(lamda) = f so you would do (3 x 10^8)/(632.99.... x 10^-9) but they just did one over the wavelength??
12. is anyone else finding time to be a bit of struggle for these papers?
13. (Original post by Rogercbinboy)
If anyone's done the January 2011 past paper could someone explain question 10.c) please.

Have no idea why the MS has made the ratio rise to the power 3.
A better way to think of it, after realising that pretty much all of the mass lies in the nucleus is that the atomic radius equals 4.6x10^-14/6x10-5 = 7.67x10^-10m

The MASS of the gold atom thus equals to 7.67x10^-10 x 1.9 x10^4 =3.6x10^-23 (m=Vxrho)

This is the same mas that is contained in the NUCLEUS because of my previous assumption.

So p = M/v = 3.6x10^-23 x (4/3pi(4.6x10-14)^3) = 8.8x10^16

V = 4/3pi(4.6x10-14)^3
14. (Original post by Jke)
If the force due to gravity is larger at the equitorial plane than the force due to the pressure difference, why does it bulge at the equator?
I'm a little confused :P
I am really confused as well. Sorry but this is something that is not explained properly... AT ALL
15. (Original post by ChicharitoH)
Haha glad I'm not the only one lol I thought that that the waves that pass in one second is just the frequency so you would use v = f(lambda) and then v/(lamda) = f so you would do (3 x 10^8)/(632.99.... x 10^-9) but they just did one over the wavelength??
Yeah, it's ridiculous. Hopefully they don't ask such a question tomorrow
16. (Original post by 41jms)
is anyone else finding time to be a bit of struggle for these papers?
Sometimes I get stuck on ONE quetion that makes me to end up wasting quite a lot of time
17. (Original post by a93)

http://www.johnbright.conwy.sch.uk/d.../G495Jun10.pdf

i dont get how the half lives is 4.
100/(2^n)=6.5
Where n = number of half lifes
2^n=(100/6.5)
n*ln2=ln(100/6.5)
n=(ln(100/6.5))/ln2
n= 3.94
18. (Original post by Unkempt_One)
Although in practice more like 80-85 for an A*, 70-75 for an A etc.
yup
19. E = kt

or

E= 1.5kt?
20. (Original post by Jke)
100/(2^n)=6.5
Where n = number of half lifes
2^n=(100/6.5)
n*ln2=ln(100/6.5)
n=(ln(100/6.5))/ln2
n= 3.94
thanks man, much appreciated =D

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