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AQA Physics PHYA5 - Thursday 18th June 2015 [Exam Discussion Thread] Watch

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    ok thanks so much , this is my method. (you don't reckon you lost any marks in calculations due to significant figs right??)

    The reason i was so worked up was becos my friend said that as technically your final answer part 1 is to 3sf , you've got to use that exact 3sf number from thereon .
    He backed himself up saying in the markschem its something like mark one for their q1b(i)* . I was just unsure if they would realise that the unrounded answer was still in reference to the answer in the previous part just unrounded. I guess examiners aren't stupid at least i hope not. Oh well thanks again , i really appreciate it - ill d it your way thanks
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    (Original post by chemphys)
    ok thanks so much , this is my method. (you don't reckon you lost any marks in calculations due to significant figs right??)

    The reason i was so worked up was becos my friend said that as technically your final answer part 1 is to 3sf , you've got to use that exact 3sf number from thereon .
    He backed himself up saying in the markschem its something like mark one for their q1b(i)* . I was just unsure if they would realise that the unrounded answer was still in reference to the answer in the previous part just unrounded. I guess examiners aren't stupid at least i hope not. Oh well thanks again , i really appreciate it - ill d it your way thanks
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    You don't lose marks for any question in the theory papers due to significant figures unless it explicitly states that you must express your answer to an "appropriate number of significant figures". In this case, it is always to the same number of significant figures as the figure with the least sig figs in the question.


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    You don't lose marks for any question in the theory papers due to significant figures unless it explicitly states that you must express your answer to an "appropriate number of significant figures". In this case, it is always to the same number of significant figures as the figure with the least sig figs in the question.


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    yes i was aware of that , it was just my friend said that as the first mark of the second part questions typically say e.g. (must have 4*their answer to part 1 ) , you must use your 3sf answer as technically that is your final answer (not the unrounded answer). I admit the wording does cause confusion but ill go with your advice because you got 91 ums
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    (Original post by chemphys)
    yes i was aware of that , it was just my friend said that as the first mark of the second part questions typically say e.g. (must have 4*their answer to part 1 ) , you must use your 3sf answer as technically that is your final answer (not the unrounded answer). I admit the wording does cause confusion but ill go with your advice because you got 91 ums
    Oh right! No I understand. The MS is confusing. Good luck with your papers



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    (Original post by CD223)
    Oh right! No I understand. The MS is confusing. Good luck with your papers



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    Thanks good luck with yours too
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    (Original post by chemphys)
    Thanks good luck with yours too
    Thank you!


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    Can any astro peeps explain what is represented by the area under a black body intensity-wavelength curve?


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    (Original post by CD223)
    Can any astro peeps explain what is represented by the area under a black body intensity-wavelength curve?


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    I'm pretty sure that it's energy. So the total energy emitted across all wavelengths is the area under the curve.

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    (Original post by _Caz_)
    I'm pretty sure that it's energy. So the total energy emitted across all wavelengths is the area under the curve.

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    Oh is it? It's just I'm so confused as to whether it's power or energy!


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    (Original post by CD223)
    Oh is it? It's just I'm so confused as to whether it's power or energy!


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    I suppose it's both because energy and power are proportional. I thought it was energy because the graph usually has intensity up the side on the y axis which is really similar to power.
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    (Original post by _Caz_)
    I suppose it's both because energy and power are proportional. I thought it was energy because the graph usually has intensity up the side on the y axis which is really similar to power.
    Yeah intensity is power per unit area - I think it is energy, I just can't understand why. I think it has something to do with Stefan's Law.
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    (Original post by CD223)
    Yeah intensity is power per unit area - I think it is energy, I just can't understand why. I think it has something to do with Stefan's Law.
    I don't know :/ I mean I suppose stefan's law means that if you double the temperature, the power with increase sixteenfold therefore more energy will be emitted so the graph should have a bigger area, thus explaining why the graphs are taller at higher temperatures. But that's just a guess :/ I'm not sure.

    Do you think black body curves will be on the exam this time? I feel like there was none of this along with the OBAFGKM on last year's paper so there could be a chance...
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    (Original post by _Caz_)
    I don't know :/ I mean I suppose stefan's law means that if you double the temperature, the power with increase sixteenfold therefore more energy will be emitted so the graph should have a bigger area, thus explaining why the graphs are taller at higher temperatures. But that's just a guess :/ I'm not sure.

    Do you think black body curves will be on the exam this time? I feel like there was none of this along with the OBAFGKM on last year's paper so there could be a chance...
    Yeah thats true - sounds along the right lines!

    I would have thought so, although I've not yet done the 2014 paper.
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    (Original post by CD223)
    Yeah thats true - sounds along the right lines!

    I would have thought so, although I've not yet done the 2014 paper.
    Woops spoilers
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    (Original post by _Caz_)
    Woops spoilers
    Haha. I've got it on 7th May though. How did you do on it?


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    (Original post by CD223)
    Haha. I've got it on 7th May though. How did you do on it?


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    Ehhhh could have been better. Please ignore the bit in the CGP book about the ratio of hydrogen to helium because it implies there is more helium than hydrogen in the universe which is wrong. That lost me like two marks in the 6 marker. Really annoyed about that as well because I was one mark off and A* in the unit 5 overall so if I'd have known the correct ratio I'd have gotten an A* in the mock. ah well at least I found out before the real thing I suppose.

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    (Original post by _Caz_)
    Ehhhh could have been better. Please ignore the bit in the CGP book about the ratio of hydrogen to helium because it implies there is more helium than hydrogen in the universe which is wrong. That lost me like two marks in the 6 marker. Really annoyed about that as well because I was one mark off and A* in the unit 5 overall so if I'd have known the correct ratio I'd have gotten an A* in the mock. ah well at least I found out before the real thing I suppose.

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    AH right, thanks for letting me know!
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    (Original post by CD223)
    AH right, thanks for letting me know!
    The actual ratio for H:He is 3:1 I think?
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    (Original post by Lau14)
    The actual ratio for He is 3:1 I think?
    I see! Thanks! How's your revision going? I've got Hubbles law onwards in astro to go, hopefully not much longer!


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    (Original post by Lau14)
    The actual ratio for He is 3:1 I think?
    Yes it is

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