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

1. (Original post by Ollie901)
I'd just say that the outsides of the earth (in the direction of the spin) have the biggest linear velocity so will have a greater circular acceleration towards the centre of the earth (v=romega, a=v^2/r) and will therefore feel a bigger centrefugal force, hence the bulge.
Don't use centrifugal in your exam, u wont get the marks.
2. (Original post by 41jms)
thank you, i sort of get it now

could you also help me with 12 d on the same paper please?
12d) I calculated the new Y value by doing ((8.19+1)x10^-14)/8.19x10^-14
This is similar to the value in i) about 1.12 so classic equation p=mv will give a reasonably accurate value.

Hope that helps.
3. (Original post by Fifi93)
12d) I calculated the new Y value by doing ((8.19+1)x10^-14)/8.19x10^-14
This is similar to the value in i) about 1.12 so classic equation p=mv will give a reasonably accurate value.

Hope that helps.
Wow, is that all you do? I was very confused by that question.
4. (Original post by Ceri25)
Can somebody please help me with uncertainties? I really get confused with absolute and percentage and whatever. Are there set formaulas that can be learnt for them?
Any examples using the pre release would be super appreciated as well!! I tried some questions from the earlier posted section c questions and I was unable to do all the uncertainty questions
Could also use the same help so bumping this - on those advance notice questions I had no idea what to divide by what.
5. (Original post by Rogercbinboy)
Could also use the same help so bumping this - on those advance notice questions I had no idea what to divide by what.
I agree with this! Whose idea were these percentage uncertainties anyways?! :/
6. (Original post by emzaz)
I agree with this! Whose idea were these percentage uncertainties anyways?! :/
I 4th this!! especially when it asked for uncertainty in length of rope.
7. http://www.hinchingbrookeschool.net/...64June2003.pdf

Guys, look at question 2a of this... how can the flux density be greater in the air gap than in the iron core, when air has a lower permeability (i.e.: it allows less magnetic field to be set up) than the iron core?
8. (Original post by Summerdays)
http://www.hinchingbrookeschool.net/...64June2003.pdf

Guys, look at question 2a of this... how can the flux density be greater in the air gap than in the iron core, when air has a lower permeability (i.e.: it allows less magnetic field to be set up) than the iron core?
I would say it's because the air gap is much thinner than the iron core, so as a result the flux lines are closer together i.e. more dense, so flux density is greater. Weird question.
9. yeh that seems really illogical, maybe because the gap is a lot, lot smaller than the core, and so even though it's less permeable it still has a bigger flux/area ratio but that it is a really stupid thing to assert as it can give people the wrong idea. 2003 was a while ago, hopefully they have matured a little since...
10. (Original post by JoeCarr)
yeh that seems really illogical, maybe because the gap is a lot, lot smaller than the core, and so even though it's less permeable it still has a bigger flux/area ratio but that it is a really stupid thing to assert as it can give people the wrong idea. 2003 was a while ago, hopefully they have matured a little since...
Hmm, maybe it's because magnetic flux is inversely proportional to area, and the area of the air gap is MUCH smaller than the iron core. It's still a ridiculous question, though!
11. how is everyone feeling about the pre-release i have a feeling it will be horrid.
12. (Original post by Birkatron)
how is everyone feeling about the pre-release i have a feeling it will be horrid.
I really hate section C. I think I have done all that I can to preper for it, though
13. I disagree, I have read through other section C's and they seem pretty standard in my opinion, plus that set of questions allow you to prepare for it perfectly. Also, the synoptic element cannot be anything too difficult as they won't expect you to work in the same level of detail for everything studied over the 2 years, just to remember the basics, so if section C is a mix of harder questions that we have prepared for and simple synoptic questions then I can't see it being that bad.....
14. (Original post by JoeCarr)
I disagree, I have read through other section C's and they seem pretty standard in my opinion, plus that set of questions allow you to prepare for it perfectly. Also, the synoptic element cannot be anything too difficult as they won't expect you to work in the same level of detail for everything studied over the 2 years, just to remember the basics, so if section C is a mix of harder questions that we have prepared for and simple synoptic questions then I can't see it being that bad.....
I hope so. Did you see January's section C for this paper...
15. (Original post by JoeCarr)
I disagree, I have read through other section C's and they seem pretty standard in my opinion, plus that set of questions allow you to prepare for it perfectly. Also, the synoptic element cannot be anything too difficult as they won't expect you to work in the same level of detail for everything studied over the 2 years, just to remember the basics, so if section C is a mix of harder questions that we have prepared for and simple synoptic questions then I can't see it being that bad.....
It's just uncertainties that are a total pain!!
16. (Original post by Summerdays)
I hope so. Did you see January's section C for this paper...
Their exponential decay question for 5 marks was pretty nice, plus i read in the examiners report that it's something that WILL come up on future papers, so it may appear on ours. I hope!
17. (Original post by Birkatron)
Their exponential decay question for 5 marks was pretty nice, plus i read in the examiners report that it's something that WILL come up on future papers, so it may appear on ours. I hope!
Wow, really? I actually hated that question. I understand that in order for something to be exponential the gradiant of the graph must decrease with the indepedent variable and that the ratio of starting and finishing values (at a constant interval of the independent variable) must be equal. And that the graph must start at a maximum value in the Y axis and then tend zero with time. But that particular question, where you suppose to take values from the graph or something? And didn't the question say something about coming up with some sort of equation? Ridiculous
18. (Original post by Summerdays)
Wow really. I actually hated that question. I understand that in order for something to be exponential the gradiant of the graph must decrease with the indepedent variable and that the ratio of starting and finishing values (at a constant interval of the independent variable) must be equal. And that the graph must start at a maximum value in the Y axis and then tend zero with time. But that particular question, where you suppose to take values from the graph or something? And didn't the question say something about coming up with some sort of equation? Ridiculous
yeah our teacher told us how to test for exponential relationships basically y0/y1 = y1/y2 and etc, as for coming up with the equation im not sure but do you do A level maths because you'll have done differential equations in that??
19. (Original post by Birkatron)
yeah our teacher told us how to test for exponential relationships basically y0/y1 = y1/y2 and etc, as for coming up with the equation im not sure but do you do A level maths because you'll have done differential equations in that??
Yeah, I have done A level maths. But still, considering this course requires no maths...
20. (Original post by Summerdays)
Yeah, I have done A level maths. But still, considering this course requires no maths...
haha i guess, maybe whoever set it just fancied being really mean.

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