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OCR Physics A G482, Electrons, Waves and Photons, 25th May 2012

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    (Original post by mashmammad)
    i mean the third line of this very ms that you have put up.
    Yes.. Current increases almost linearly with increase in P.D.
    R=V/I If current is increasing almost linearly, resistance is decreasing. Go check it for yourself.
    Why are you even telling me to look at that line? That doesn't suggest resistant is constant in any way what so ever.

    If you gave yourself full marks for that question in a past paper, you're marking it wrong.
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    (Original post by HarryW95)
    Yes.. Current increases almost linearly with increase in P.D.
    R=V/I If current is increasing almost linearly, resistance is decreasing. Go check it for yourself.
    what???? linear means constant instantaneous resistance. you may have a line that doesnt go through origin. but it doesnt mean the gradient is not constant.
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    (Original post by mashmammad)
    what???? linear means constant instantaneous resistance. you may have a line that doesnt go through origin. but it doesnt mean the gradient is not constant.
    You're making this so much more difficult than it needs to be.. Because you seem to be some what incapable to interpreting a graph, I've got the values for you.

    http://gyazo.com/eafb7b433afb3946ae23333e57aa99f6

    [R=V/I]
    At 1.8 V = 1.8/9x10^-3 = 200 ohms
    At 2.0 V = 2.0/38x10^-3 = 52.63 ohms

    Hence the resistance is decreasing. Are we done here..?
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    no. what you are saying is just true if the graph was a line through origin. trust me mate, i dont have time to argue with you, but i asure you that this is wrong. but just promise if any of us was wrong let the other know through a message. on tsr of course.
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    (Original post by mashmammad)
    no. what you are saying is just true if the graph was a line through origin. trust me mate, i dont have time to argue with you, but i asure you that this is wrong. but just promise if any of us was wrong let the other know through a message. on tsr of course.
    No, what YOU are trying to say is only valid if the line passes through the origin. It is not wrong and the markscheme clearly states that. The markscheme doesn't state that resistance is constant and there is one reason for that; because it isn't. My last post clearly shows resistance is decreasing after 1.8V and you can't argue with the figures.
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    The resistance of the LED decreases. This can be demonstrated by calculating two values from the graph. A constant gradient doesnt mean a constant resistance - the current was increasing at a greater rate than the p.d
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    (Original post by tooty_fruit)
    The resistance of the LED decreases. This can be demonstrated by calculating two values from the graph. A constant gradient doesnt mean a constant resistance - the current was increasing at a greater rate than the p.d
    Thank you.. :rolleyes:
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    (Original post by Nick_)
    only if the line would go through the origin if you continued it which it did not, hence resistance was changing and in this case it was decreasing

    this is because R does not equal dV/dI, it just equals V/I
    This is genius.
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    if we all done that paper together, we would have aced it lol

    can someoine do the mark scheme
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    (Original post by Ionus7)
    I put 0... Darn it. Now I know why that makes sense. D'OH!
    the answer is infinite resistance. this i because there was another similar question and was asked what the resistance is before that voltage. when looking at the mark scheme, it specifically said " infinite resistance do not accept 0 Ohm"

    there u go
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    (Original post by Malabarista)
    Thanks, also, please tell me for Q6 wave pulse one anyone here got something like this:

    Attachment 151301
    bloody hell, if you drew something like that in the exam earlier on, you would get a zero for that one. youre trying to violate their work
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    can someone please tell what the grade boundaries for an A was last year and jan 2012?? thanks
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    Am I the only one that felt that this paper was easier than previous papers?
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    (Original post by emah123)
    can someone please tell what the grade boundaries for an A was last year and jan 2012?? thanks
    73/100
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    (Original post by emah123)
    can someone please tell what the grade boundaries for an A was last year and jan 2012?? thanks
    They're generally all between 67 and 73 in the past few years.
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    this was paper was not easier than jan 2012 end of
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    (Original post by LewisMead)
    They're generally all between 67 and 73 in the past few years.
    exactly so why should this paper be higher
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    (Original post by Theafricanlegend)
    this was paper was not easier than jan 2012 end of
    Yeah. Jan 2012 was very straight forward and plain.
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    (Original post by Sarabande)
    Yeah. Jan 2012 was very straight forward and plain.
    meaning that grade boundaries will be lower than 73.
    my guess : 70-MAYBE69 for an a
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    (Original post by Theafricanlegend)
    exactly so why should this paper be higher
    I have not once said it would be.

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