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June 2011 G485-Fields, Particles and Frontiers of Physics

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Reply 980
Avatar for emyholdem
emyholdem
Did anyone else notice the mistype on the paper.

We had our exams officer come in and stop us halfway through. There was an error on Q3, during the text above the diagram it said the seperation between the plates was 0.05cm, however on the diagram it said 0.05m, so therefore a complete contradiction.

Our exams officer had spoken to OCR on the phone during the exam and was annoyed.

It was meant to be 0.05m in the text.
Reply 981
Avatar for yu80359
yu80359

I think if I get more than 60marks on this paper should be a B for sure?
Original post by susan23
was that the question where it said 0.05cm and then 0.05m?


Yeah
Original post by Oh my Ms. Coffey
Water is the moderator.


Water can be used as the coolant. Graphite is used for moderators as fast moving neutrons make inelastic collisions with the graphite, causing them to lose Ek and hence greater probability of being absorbed into a U-235 atom.
Reply 984
Avatar for Franklin
Franklin
Original post by Oh my Ms. Coffey
Water is the moderator.


Actually it can be water or graphite...depending on the type of reactor which the question didn't specify
Original post by CharleyChester
Just so everyone knows, there was a mistake in question 3 part c. Our exam invigilator came in half way through our exam and told us :s-smilie:


I notified our invigilator about the 2 mistakes. I reckon they musta been new at this, because a look of sheer terror came on their face :P
Original post by susan23
actually its carbon but I wrote barium for some ****ed up reason!


From revision guide

'U235 fuel rods need to be place in a moderator for example water to slow down/absorb neutrons.'
Reply 987
Avatar for susan23
susan23
3
Original post by ViralRiver
I said force was upwards using FLHR. Current went from right to left (or left to right if you use FRHR) - as electron flow is opposite to conventional. Field was sort of coming towards you, so force goes upwards. Hence reading on scale goes up by 0.016N.


But I thought current is left to right and motion is perpendicular..the motion acts downwards..so the force act downwards no? so it was 2.516N on scale?? :s I'm wrong right?
2 mistakes oO - out invigilators are **** and didn't tell us about any mistakes =\ .
Both work, but carbon is better since it's chemically inert.
Reply 990
Avatar for susan23
susan23
3
Original post by Oh my Ms. Coffey
From revision guide

'U235 fuel rods need to be place in a moderator for example water to slow down/absorb neutrons.'


Oh ok, I read it can be carbon too.
Original post by ViralRiver
Water can be used as the coolant. Graphite is used for moderators as fast moving neutrons make inelastic collisions with the graphite, causing them to lose Ek and hence greater probability of being absorbed into a U-235 atom.


Again from revision guide 'often the coolant is the same water being used in the reactor as the moderator'
Original post by apo1324
Did anyone get any extra time because of the mistake? I got 10 mins extra. :biggrin:


No and i think its wrong you did, the same conditions should apply to every candidate, wether no-one gets extra time or everyone does.
Reply 993
Avatar for apo1324
apo1324
11
The conventional current for 5 is going from left to right, I have the paper. Field coming towards you therefore downwards.
Reply 994
Avatar for susan23
susan23
3
Original post by CharleyChester
Yeah


lol...I wrote on the paper..."errr hello you did a mistake here!!" I was gna swear...but i though allow it :colondollar: what happens if theres a mistake? do they give everyone full marks?
Original post by susan23
But I thought current is left to right and motion is perpendicular..the motion acts downwards..so the force act downwards no? so it was 2.516N on scale?? :s I'm wrong right?


My understanding is you go by conventional flow for a positive charge - in which case it would be left to right. But because it was an electron, you either reverse the current using FLHR, or use FRHR instead.
Reply 996
Avatar for lpmad
lpmad
Original post by Franklin
No.

left hand rule uses direction of conventional current and therefore giving the force upwards


Conventional current is +ve to -ve
X was connected to the +ve terminal therefore convention current is from left to right, magnetic field was technically out of the paper therefore force is downwards
Original post by Oh my Ms. Coffey
Again from revision guide 'often the coolant is the same water being used in the reactor as the moderator'


Well I guess both can be used. Graphite is the example given in the OCR Cambridge book (not Heinneman).
Original post by Kalamari Dave
I notified our invigilator about the 2 mistakes. I reckon they musta been new at this, because a look of sheer terror came on their face :P


Two mistakes? I only noticed the distance one. :confused:
Reply 999
Avatar for Franklin
Franklin
Original post by Oh my Ms. Coffey
Again from revision guide 'often the coolant is the same water being used in the reactor as the moderator'


It can be water or graphite depending on the type of reactor, which the question did not specify

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