June 2011 G485-Fields, Particles and Frontiers of Physics Watch

susan23
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#981
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#981
(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
was that the question where it said 0.05cm and then 0.05m?
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emyholdem
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#982
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#982
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.
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yu80359
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#983
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#983
I think if I get more than 60marks on this paper should be a B for sure?
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CharleyChester
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#984
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#984
(Original post by susan23)
was that the question where it said 0.05cm and then 0.05m?
Yeah
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ViralRiver
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#985
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#985
(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.
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Franklin
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#986
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#986
(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
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Kalamari Dave
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#987
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#987
(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
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
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Oh my Ms. Coffey
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#988
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#988
(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.'
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susan23
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#989
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#989
(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?
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ViralRiver
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#990
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#990
2 mistakes oO - out invigilators are **** and didn't tell us about any mistakes =\ .
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Captain Hob
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#991
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#991
Both work, but carbon is better since it's chemically inert.
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susan23
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#992
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#992
(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.
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Oh my Ms. Coffey
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#993
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#993
(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'
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In the looney bin
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#994
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#994
(Original post by apo1324)
Did anyone get any extra time because of the mistake? I got 10 mins extra.
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.
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apo1324
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#995
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#995
The conventional current for 5 is going from left to right, I have the paper. Field coming towards you therefore downwards.
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susan23
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#996
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#996
(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 what happens if theres a mistake? do they give everyone full marks?
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ViralRiver
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#997
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#997
(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.
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lpmad
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#998
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#998
(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
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Captain Hob
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#999
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#999
(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:
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ViralRiver
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#1000
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#1000
(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).
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