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

1. For the minimum, I put something about how not necessarily all of the beta particles were being detected - if there were more that weren't detected, then the activity was actually higher than measured, and so there'd be more nuclei than the amount calculated, so that was just the minimum. Not too sure though.
2. (Original post by Jke)
Doesn't that also mean more than half of the atoms could decay each half life?
So in fact it isn't the minimum number? It's the minimum number on average?
Not sure if more than half can decay who knows, that would be the only thing to explain it though surely?
3. I think the answer to why it was minimum number was that some of the radiation will be absorbed by the source itself :/ not sure tho
4. (Original post by Revolution is my Name)
Yup. Which made me wonder whether they just wanted you to quote those, or come up with some different ones.
If so there goes 4 marks. Stupid question though since they'd written all the points that I'd have thought of anyway.
5. What did people get for the ratio? Was it slightly under 1 or slightly above? Also I got 1.5 x10-12 where it said show that something is about 3x10-11 J.

Also for the plate thingy I said the beta particles ionise the air, and those electrons transfer charge to the positive ball reducing it's overall charge. Therefore there is less force and less extension.
What did people get for the ratio? Was it slightly under 1 or slightly above? Also I got 1.5 x10-12 where it said show that something is about 3x10-11 J.

Also for the plate thingy I said the beta particles ionise the air, and those electrons transfer charge to the positive ball reducing it's overall charge. Therefore there is less force and less extension.
i got slightly above and 2.9ish x10^-11
What did people get for the ratio? Was it slightly under 1 or slightly above? Also I got 1.5 x10-12 where it said show that something is about 3x10-11 J.

Also for the plate thingy I said the beta particles ionise the air, and those electrons transfer charge to the positive ball reducing it's overall charge. Therefore there is less force and less extension.
I got like 1.005 or something as the ratio, and for that energy question I think I got x10-11 not x10-12.
8. Yeah I knew I got the joule one wrong but hopefully as the next part was use your answer I will get ecf marks. And damn I got slightly under 1 lol.

Not a bad paper but not amazing. Hopefully low/mid 80s ??
What did people get for the ratio? Was it slightly under 1 or slightly above? Also I got 1.5 x10-12 where it said show that something is about 3x10-11 J.

Also for the plate thingy I said the beta particles ionise the air, and those electrons transfer charge to the positive ball reducing it's overall charge. Therefore there is less force and less extension.
I got 1.006 or something like that, and 2.99*10^-11 for the energy.
Also I got 1.5 x10-12 where it said show that something is about 3x10-11 J.

.
That's what you'd get for the energy given out by fission question, if you forgot to multiply the MeV per nucleon by the number of nucleons involved.
Also for the plate thingy I said the beta particles ionise the air, and those electrons transfer charge to the positive ball reducing it's overall charge. Therefore there is less force and less extension.
Thats what i put it was in "jan 2010, legacy, field and particle pics" question 10 b iv
12. (Original post by Revolution is my Name)
That's what you'd get for the energy given out by fission question, if you forgot to multiply the MeV per nucleon by the number of nucleons involved.
Oh yeah of course silly me. lol. damn. was trying for a* hopefully i can still get it.
14. I thought it went really well.
15. Thought it was a good paper.
Already realising i've made some stupid mistakes though. Couldn't do the relativistic factor one by any means, kept getting v to be greater than c.
16. that was a straight forward paper...

but i wished i spent less time revising Section C... and did the theory before...

70% were really easy questions...... and then 30% were pretty hard.... so how the hell are they going to tell the difference between B-D.. grade people
17. I thought the paper was ok but by no means easy or impossible. Section A and B were quite straight forward although I got confused on the risk of cancer question for some reason and the one about the number of nuclei being a minimum :/ What did people get for the risk question? I got like 4.4 or something (it was one mark also). I said that the number of nuclei calculated was a minimum because the decay constant is only a probability it does not tell you that a set number of nuclei are going to decay in one second so I said that the number of nuclei calculated was a minimum because you probably would need more nuclei to satisfy the activity required as many of the nuclei will not actually decay as calculated in one second. However I think answers about the detector not measuring the full activity is probably what they were looking for :/ Also for section C for the last question I got a little confused did anyone else say that using the frequency of the laser you could work out the wavelength of the laser beam and then divide 1 by that number to get the number of wavelengths in a metre then times this number by the wavelength distance to get the length of a metre haha. Seemed a bit weird thinking back... :/ Other than that I think it went ok x
18. (Original post by Alex.Stevens)
Thought it was a good paper.
Already realising i've made some stupid mistakes though. Couldn't do the relativistic factor one by any means, kept getting v to be greater than c.
I also found that one tricky, although thought I knew what I had to do!

All-in-all not a bad paper, could have been much worse. Didn't get majorly stuck on anything and atleast I finished this time (damn you G491 resit!)!
19. (Original post by b_white)
Was it OCR A or B with this fail? http://www.bbc.co.uk/news/education-13857911

'An error in a question in the A-level physics paper, taken on Tuesday morning, used the wrong measurements.

A candidate taking the OCR exam paper told the BBC that pupils "were given a few minutes extra in our exam when the mistake was spotted and it caused some disruption".'
A.
20. Did anyone else do the very last question of section C? I had no idea and so just wrote down what it said in the pre release article and added stuff about using the emission/absorption spectrum of caesium??? massive flop

but overall not too bad a paper

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