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AQA Physics PHYA4 - Thursday 11th June 2015 [Exam Discussion Thread] Watch

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    (Original post by PotterPhysics)
    No problem! This is exactly how I would do it in an exam because it's the first approach that came to mind and takes at most a few seconds to carry out if you know what you're doing, but CD's one is definitely nicer. (What I did would best be described as a "bash".)
    Lol mine was more logic than maths (I chose the dumb way ). I tend to prefer logical thinking but I do appreciate its impressive if you can manage the maths. I certainly couldn't under pressure haha.


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    (Original post by Jimmy20002012)
    Yes it is June 2014, has some pretty tough multi choice questions in there. Thanks for that makes much more sense.


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    Yeah hardest MC one I've seen. Some interesting ones though! No worries.


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    (Original post by CD223)
    Lol mine was more logic than maths (I chose the dumb way ). I tend to prefer logical thinking but I do appreciate its impressive if you can manage the maths. I certainly couldn't under pressure haha.


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    Nah, mathematicians would definitely prefer your method as being more "elegant". (Side note: That was nothing compared to STEP, where you have to crunch through much harder calculations without a calculator.)
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    (Original post by PotterPhysics)
    Nah, mathematicians would definitely prefer your method as being more "elegant". (Side note: That was nothing compared to STEP, where you have to crunch through much harder calculations without a calculator.)
    Well thank you for the compliment, but your method is more impressive

    Oh wow...it's got to the point I've now given up being in awe of the people on this site. I got 40/100 on the MAT last year, that shows how far off I am to people on this thread 😂 good luck on STEP


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    (Original post by Mehrdad jafari)
    That's true. For me studying it makes unit 4 acceptable.
    I've heard the astro option is the hardest alongside medical one. Though i found the waves chapter a bit abstract and hard to tolerate


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    Thats weird, I think astro is the easiest option. Much easier than turning points definitely. Its just a load of new stuff to learn, thats all. Not to mention its quite an interesting topic (stars and all) :P


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    (Original post by CD223)
    It's the hardest Capacitance question I've seen. June 2014, right?

    Essentially, as E \propto V^2, this means that, if we set E = 1600\mu J, then when V has decreased by 2.0V, E has become \frac{E}{4} = 400\mu J.

    As E has decreased by a factor of 4 and E \propto V^2, V must have decreased by a factor of 2 \left(\sqrt{\frac{V^2}{4}}\right  ).

    As V has halved by decreasing by 2.0V, the initial pd must have been 4.0V.

    This follows that, as E = \frac{1}{2}CV^2,

    C = \frac{2 \times 1600 \times 10^{-6}}{4^2}

    

\therefore C = 200 \times 10^{-6}F


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    Hmmmmmmmmmmmmmmmmmmmm. That sounds like essentially what I've done. Here's what I did.
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    (Original post by zaybun)
    Thats weird, I think astro is the easiest option. Much easier than turning points definitely. Its just a load of new stuff to learn, thats all. Not to mention its quite an interesting topic (stars and all) :P


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    Well, I think that's what makes it harder or even medical physics one basically. Astro is 4 chapters and medical 5 chapters whereas turning points is only 3 chapters. Even though turning points may be harder, the content is logical and reasonable and there is not so much in it that seem being beyond the scope of the A2 specification.


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    It seems we won't see the EMPA mark scheme until 10 says after the actual exam


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    (Original post by PotterPhysics)
    Alternative (and longer!)

    We are given information about V and we need to find C, so the equation to use is E=\frac{1}{2}CV^2. Initially, E_0=\frac{1}{2}CV^2=1600\mu implying that CV^2=3200\mu. Then the voltage decreases by 2V and the energy stored becomes 400\mu, which we can express as the equation E_1=\frac{1}{2}C(V-2)^2=400\mu, or C(V-2)^2=800\mu.

    Now square rooting both sides of each equation we obtain V\sqrt{C}=\sqrt{3200\mu} and (V-2)\sqrt{C}=\sqrt{800\mu}. Thus V=\frac{\sqrt{3200\mu}}{\sqrt{C}  }=\frac{\sqrt{800\mu}}{\sqrt{C}}  +2, or equivalently \sqrt{3200\mu}-\sqrt{800\mu}=2\sqrt{C}. Now we just square both sides and divide by 4 to get C=\frac{(\sqrt{3200\mu}-\sqrt{800\mu})^2}{4}=200\mu F
    Finally make sense !!
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    (Original post by dominicwild)
    Hmmmmmmmmmmmmmmmmmmmm. That sounds like essentially what I've done. Here's what I did.
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    Yeah that is! Mine was just less algebra haha.

    (Original post by Mehrdad jafari)
    It seems we won't see the EMPA mark scheme until 10 says after the actual exam
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    Oh no, is that 10 days after PHYA4?



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    (Original post by CD223)
    Oh no, is that 10 days after PHYA4?



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    I'm still not sure if that's the case because the exam papers taken in the last 10 days have been released



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    (Original post by Mehrdad jafari)
    I'm still not sure if that's the case because the exam papers taken in the last 10 days have been released



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    It's just it's been more than 10 days (11 days actually) since the last date the EMPA was taken on?


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    (Original post by CD223)
    It's just it's been more than 10 days (11 days actually) since the last date the EMPA was taken on?


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    Yeah, true, I really don't know what's happening. If the files are released electronically then we would have the papers by now which I don't think is the case. And if the files are released manually then they will be released by the end of today or maximum tomorrow


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    Has anyone got any tips for revising the transformer questions, ive done all the new past papers but its wasn't included in the old syllabus. Has anyone got any resources?
    thanks!!
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    https://60abffc9b401b1c0936e01291c15...%20Physics.pdf

    Can anyone help with question 14? thanks a lot
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    (Original post by getback339)
    https://60abffc9b401b1c0936e01291c15...%20Physics.pdf

    Can anyone help with question 14? thanks a lot
    Check out on page 90, post 1791 where CD223 provided an explanation


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    (Original post by Mehrdad jafari)
    Yeah, true, I really don't know what's happening. If the files are released electronically then we would have the papers by now which I don't think is the case. And if the files are released manually then they will be released by the end of today or maximum tomorrow
    Hope so! Wanna see how badly I did 😖

    (Original post by getback339)
    https://60abffc9b401b1c0936e01291c15...%20Physics.pdf

    Can anyone help with question 14? thanks a lot
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    (Original post by CD223)
    Hope so! Wanna see how badly I did 😖
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    Even though I messed up in that paper too, I'm still looking forward to seeing that lol


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    can anyone help with jan 2010 - q21?? I keep getting C ;(

    Thanks
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    (Original post by gcsestuff)
    can anyone help with jan 2010 - q21?? I keep getting C ;(

    Thanks
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