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ANSWERS: OCR Physics B(Advancing Physics) G491~ 20th May 2014~ AS Physics Watch

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    I managed to finish all of the paper and check
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    (Original post by JagdPanther)
    Are you sure? cos somehow I rmb that it says '2.2V across the LDR' written in the question itself. Or maybe its just my mind making an image of that up.

    Well anyone rmb if that was in the question?
    The 800 ohm was R the fixed resistor. So yes there was 2.2 across the LDR. This means that the resistance of the LDR must be less than that of the fixed resistor R as V=IR and I is the same in a potential divider and R is constant.

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    (Original post by JediMaster1997)
    What did people get for the question at the bottom of the first page on section A. Where you were given a graph and had to work out the frequency??
    0.225 or something
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    (Original post by JagdPanther)
    What I rmb was that the total p.d. is 6V and there are 2.2V across the 800ohm resistor. (I really think that it was stated in the question, the fixed resistor hving 2.2V)
    If the resistance for the LDR is 463ohm, how can it shares more voltage(6-2.2 = 3.8V) than the 800ohm fixed resistor?

    Because OCR logic, yes.
    No, the 800 ohm resistor had a 3.8V, which is what was read off the graph, and the LDR had 463 ohm (and so 2.2V). I can't remember any pds stated in the question but idk

    Vin/Vout = Rtotal/Rout
    6/3.8 = (800 +R) /800

    blah blah blah R = 463
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    (Original post by Adam971)
    0.225 or something
    Frequency = 1/period, the period was something in milliseconds so the frequency was much greater than that
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    I did this exam earlier, yesterday I did OCR's C1 exam and finished in half an hour, so had an hour of absolute boredom afterwards, so I was initially happy that this exam was only 1 hour long, and then felt foolish for being happy about that since I didn't finish (I think I had two 3 mark questions on lenses left, and I had no time to check through my work). Usually I'm very quick with papers, but that was just surprisingly time restricting.

    I'm relieved that so many people also found it a horrible paper, as that means grade boundaries should be nice and low. If they're 34/60 or higher than I will be royally pissed though, as this paper was MUCH harder than the January 2010 one!

    Everyone complaining about the QR question and others like "Oh no it was obvious!"
    If it makes anyone feel better I put that the 3 squares were there to see if any distortion has occurred due to noise as it would be difficult to tell in the other section as it appears to be spread randomly (the only thing my brain would come up with).

    For all I know I could've messed up all my calculations. I'd like to think I got 40/60 on that, maybe 30...I really want an A in Physics though, I did 7 past papers and got As in all of them. My coursework is one mark off an A going by last year's grade boundaries. Just have to hope that Unit 2 is nicer than this

    I haven't spoken to anyone from my school who does physics, but as soon as I left the exam room the first thing I heard was some guy from my class saying how horrible it was to his friends, and then another guy from my class asking his friends if they finished, because he didn't. None of them finished either.

    I feel like we're the guinea pig year, and it sucks Trying scrapped January exams, trying new exam papers, we're destined to fail.

    Hate OCR B sooo much, which is a shame because I find the content really interesting at times.
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    This paper was just ridiculous. Firstly, 1 hour is not long enough to complete a g491 paper, especially this one. Secondly, the last 8 marks about lenses and CCDs was almost impossible to answer in the time that we had left and was really difficult for a unit 1 paper. Section A on the whole was ok but section B was ridiculous. We had to name two uses of graphene and the properties for that use which wasn't really related to the specification. The grade boundaries will probably be significantly lower than in previous papers because a lot of people failed to do the final 8 marks. A grade C will probably be around 31, a B about 35 and an A about 39.
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    (Original post by james-aitken)
    Frequency = 1/period, the period was something in milliseconds so the frequency was much greater than that
    yeah I know I've probably done it wrong. It was hard for one of the first questions, but was only 1 mark.
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    For the potential divider question, if I rounded my resistor value to 460 ohm, (2 SF), will I lose a mark do you think?
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    To finish g491 you just need to know what you are talking abouit doesn't take long to sub numbers in formulae. Maybe Ocr wanted to make their papers more challenging because to be honest the ones from previous years were too easy. I think at times everyone just wants a 'free' A and aren't willing to genuinely learn and understand physics in a wider context
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    (Original post by emfp21)
    How are we supposed to know the units for charge carrier density,
    Errr... because its a density? D = Mass/Volume so in that list you were looking for a mass and a volume^-1. The only one in the list that had both of those was kgm^-1.
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    (Original post by MasterOfTheSwag)
    For the potential divider question, if I rounded my resistor value to 460 ohm, (2 SF), will I lose a mark do you think?
    I doubt it, the markschemes usually have 2sf as standard then "Allow answer to 3sf" in the additional guidelines bit, you should be good to go on that one.
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    (Original post by Okkefac)
    I did this exam earlier, yesterday I did OCR's C1 exam and finished in half an hour, so had an hour of absolute boredom afterwards, so I was initially happy that this exam was only 1 hour long, and then felt foolish for being happy about that since I didn't finish (I think I had two 3 mark questions on lenses left, and I had no time to check through my work). Usually I'm very quick with papers, but that was just surprisingly time restricting.
    *sigh* if only the C1 time can be transferred to Physics... I was so bored I started checking my differentiations with chain/product/quotient rules to see if they worked :/
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    The correct answer for the density one was m^-3, my teacher told us afterwards. Electrons have negligible mass. The density is just the number of electrons in a given volume. Got that one completely wrong too :/
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    (Original post by JonnyXDA)
    Errr... because its a density? D = Mass/Volume so in that list you were looking for a mass and a volume^-1. The only one in the list that had both of those was kgm^-1.
    The amount of charge carriers isn't measured by mass though, it's just a number, so the answer was simply m^-3.

    They put the normal density units in there to throw people off
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    (Original post by mynamewontfit)
    To finish g491 you just need to know what you are talking abouit doesn't take long to sub numbers in formulae. Maybe Ocr wanted to make their papers more challenging because to be honest the ones from previous years were too easy. I think at times everyone just wants a 'free' A and aren't willing to genuinely learn and understand physics in a wider context
    I think you're being a bit unfair there. It was significantly harder than what we expected - time wise. I'm sure myself and the rest of the top end of our physics class would have easily completed that with an extra half hour but we found that we didn't have time to fill in some of the more challenging to interpret questions with the time pressure.

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    (Original post by JonnyXDA)
    Errr... because its a density? D = Mass/Volume so in that list you were looking for a mass and a volume^-1. The only one in the list that had both of those was kgm^-1.
    Apparently the right answer was supposed to be m^-3, because charge carriers are measured in numbers, not kgs
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    The unit was m-3... i put kgm-1 as well but wiki says m-3
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    (Original post by JediMaster1997)
    The correct answer for the density one was m^-3, my teacher told us afterwards. Electrons have negligible mass. The density is just the number of electrons in a given volume. Got that one completely wrong too :/
    Ah crap, you're right - oops, there goes another 1 of my precious marks:eek:
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    (Original post by LimbuRonit)
    Thanks bud always good to hear a support! I hope you get into med school
    Good luck for the other exams mate.
    Dentistry is boring anyway

    Joking, I'm sure you'll get in - this exam is only 30% remember
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    (Original post by JonnyXDA)
    Ah crap, you're right - oops, there goes another 1 of my precious marks:eek:
    Don't worry, I only know one guy who got that right and hes a total genius. Ive lost so many marks... :'(
 
 
 
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