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

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1. (Original post by vit1008)
did anyone else get like 4.96 kg for the mass of uranium used??
I got this but the general consensus is that it isn't the right answer
2. (Original post by vit1008)
did anyone else get like 4.96 kg for the mass of uranium used??
Think I got 1700-ish kg...Does anyone actually know what the proper answer was for that one?
3. When are the actual answers going to be posted online?!?
4. (Original post by Harry-AA)
I got this but the general consensus is that it isn't the right answer
I got the same, fairly certain its right.
5. The answer to the X-Ray Q was 400 and something people.
6. If everyone is saying they found it easier than other past papers grade boundaries will be higher not lower than previous G495 papers.
7. (Original post by war833)
The answer to the X-Ray Q was 400 and something people.
It wasn't it was 4.25 because I got 425 but used 3 instead of 0.03 for 3%
8. (Original post by Geekchic17)
I used the normal equation, i thought it would be average because the normal flux linkage/time graph is a curve, but we calculated the straight line gradient between the points and 0... so i guessed that our equation didn't take into account this curve?

but the normal equation assumes that the ring is cutting through the maximum amount of flux over the entire time period - it gives a peak emf not an average one
9. (Original post by Harry.C)
I got the same, fairly certain its right.
But so many people got around 1000kg... but that is hella' lot of uranium
10. (Original post by kttt101)
but the normal equation assumes that the ring is cutting through the maximum amount of flux over the entire time period - it gives a peak emf not an average one
the rate of change of flux was the change in flux (all of it cos it drops to 0) divided by the change in time (which was given). Was it not just this? There was no peak because it was a constant flux and not alternating?
11. (Original post by kttt101)
but the normal equation assumes that the ring is cutting through the maximum amount of flux over the entire time period - it gives a peak emf not an average one
That's only if you find the 1/4 period and used that as your dt. If not, then that's not the case, I think.
12. (Original post by Harry-AA)
the rate of change of flux was the change in flux (all of it cos it drops to 0) divided by the change in time (which was given). Was it not just this? There was no peak because it was a constant emf and not alternating?
The emf was changing because it rotated 1/4 of the way.
13. (Original post by Harry-AA)
the rate of change of flux was the change in flux (all of it cos it drops to 0) divided by the change in time (which was given). Was it not just this? There was no peak because it was a constant emf and not alternating?

question asked for an ''average emf''

if you think about it rotating - at the end its perpendicular to field lines so cuts more lines at the end of the rotation, so generates more emf
If everyone is saying they found it easier than other past papers grade boundaries will be higher not lower than previous G495 papers.
I dont think they can raise the grade boundaries over 80% for an A, can they...
15. (Original post by Harry-AA)
But so many people got around 1000kg... but that is hella' lot of uranium

think 1000kg per year is pretty close to whats actually used
16. (Original post by war833)
The answer to the X-Ray Q was 400 and something people.
435 to be precise....
17. (Original post by kttt101)
question asked for an ''average emf''

if you think about it rotating - at the end its perpendicular to field lines so cuts more lines at the end of the rotation, so generates more emf
when it's perpendicular there is no flux running through it so the change in flux is just the flux at the start.
18. (Original post by Summerdays)
The emf was chaging because it rotated 1/4 of the way.
I meant flux, I always write those two the wrong way round.
19. (Original post by Harry-AA)
I meant flux, I always write those two the wrong way round.
Yeah, but it cuts more flux near the end of it fall
20. (Original post by Harry-AA)
It wasn't it was 4.25 because I got 425 but used 3 instead of 0.03 for 3%
But it was a percentage of people, so you times'd 3 by 2x10^-5 to get percentage chance, then multiplied it by no. of people to get the likely number of people this will mean get cancer, then time it by 25 :/ I think. ? Might be wrong but I did consider using 0.03...

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