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

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    What derivations do we need to know in the 'Gases' chapter of the book? Theres that long kinetic theory one. Anything else?
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    (Original post by Mehrdad jafari)
    Charles' Law can be used to find how the volume of a fixed mass of gas at a constant pressure varies with temperature. Plotting experimental results of Charles's Law allows the absolute zero to be found.

    Explain how absolute is zero determined using an experiment and state one assumption made when determining the absolute zero


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    For a fixed mass of gas at a constant volume, the Pressure applied by the gas is proportional to the Temperature of the gas.

    By using a thermometer and a pressure sensor, one could simply heat a fixed mass of gas at a constant volume and record different values and repeats (average) for Temperature and Pressure.

    Then plot a graph of Pressure against Temperature and obtain a straight line curve which can be extrapolated to show that the pressure by the gas is 0 when the temperature is 0.

    Assumption is that gas is kept at a constant volume.
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    I don't get why people memorize previous six markers. I only use them to aid with my understanding of select topics such as nuclear reactors, but there's no point memorizing them word for word as if one of them will come up.
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    (Original post by Specter)
    What derivations do we need to know in the 'Gases' chapter of the book? Theres that long kinetic theory one. Anything else?
    Nope that's the only one.

    There is the one where they derive pV=\frac{1}{3}Nm\overline{c}^2 and another one where they plug in pV=NkT into the left side of this equation and rearrange to get \frac{1}{2}m\overline{c}^2=\frac  {3}{2}kT (kinetic energy of an ideal gas is directly proportional to temperature in K)
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    (Original post by PotterPhysics)
    Nope that's the only one.

    There is the one where they derive pV=\frac{1}{3}Nm\overline{c}^2 and another one where they plug in pV=NkT into the left side of this equation and rearrange to get \frac{1}{2}m\overline{c}^2=\frac  {3}{2}kT (kinetic energy of an ideal gas is directly proportional to temperature in K)
    How did you find unit 4? i struggle with unit 5 in comparison tbh.


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    (Original post by betbi3etwerrd)
    For a fixed mass of gas at a constant volume, the Pressure applied by the gas is proportional to the Temperature of the gas.

    By using a thermometer and a pressure sensor, one could simply heat a fixed mass of gas at a constant volume and record different values and repeats (average) for Temperature and Pressure.

    Then plot a graph of Pressure against Temperature and obtain a straight line curve which can be extrapolated to show that the pressure by the gas is 0 when the temperature is 0.

    Assumption is that gas is kept at a constant volume.
    Quite well cracked but unfortunately the measurements taken are volume against temperature at constant pressure. Because i gave you hint in the question by stating what Charles's law was then you will lose some of your positive marks, resulting in deduction of all your marks.
    The assumption made is that the volume of the gas is zero at absolute zero which in principle this would be the volume of all the atoms/molecules of the gas in the experiment.


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    (Original post by Mehrdad jafari)
    Quite well cracked but unfortunately the measurements taken are volume against temperature at constant pressure. Because i gave you hint in the question by stating what Charles's law was then you will lose some of your positive marks, resulting in deduction of all your marks.
    The assumption made is that the volume of the gas is zero at absolute zero which in principle this would be the volume of all the atoms/molecules of the gas in the experiment.


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    Lol the misread. Was wondering if they tell you what the name of the law refers to like you did because I don't remember the names like Charles law is for this.
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    (Original post by betbi3etwerrd)
    Lol the misread. Was wondering if they tell you what the name of the law refers to like you did because I don't remember the names like Charles law is for this.
    Yeah, they would definitely. Charles doesn't mean anything, his law means something


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    (Original post by CD223)
    How did you find unit 4? i struggle with unit 5 in comparison tbh.


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    Written paper was nice overall except for problem 1c(?) which took some time (but I got it in the end). Multiple choice was easy but I got caught out by the wires question so looking at 24/25 there. I'm assuming it went well for you? ;-)
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    I thought unit 5 was going to be straight forward when I was doing unit 4, but now I realise I've seriously underestimated unit 5 😭😭😭


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    Anyone here doing the medical physics option? It's SUCH a chore to learn, so much information! But the grade boundaries are awfully favourable
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    Hey what are people using for Unit 5A revision? Teachers notes?
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    Anyone know where the mark schemes for June 2008 are.. (not available on AQA)
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    (Original post by PotterPhysics)
    Written paper was nice overall except for problem 1c(?) which took some time (but I got it in the end). Multiple choice was easy but I got caught out by the wires question so looking at 24/25 there. I'm assuming it went well for you? ;-)
    Cocked up the written paper. Got 24/25 on the MC but messed up the damping question. Also drew the current graph wrong and definitely didn't get 6/6 on the six marker.

    How are you revising for unit 5?


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    @Turning points people:

    Are we meant to know \frac{e}{m}=\frac{2yd}{V_pt^2} for an electron beam moving in the electric field between two plates. (There's another one for an electron beam in fine beam tube: \frac{e}{m}=\frac{2V}{B^2r^2})
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    Explain why sources of β radiation often also produce γ rays of discrete frequencies. (3)
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    (Original post by PotterPhysics)
    @Turning points people:

    Are we meant to know \frac{e}{m}=\frac{2yd}{V_pt^2} for an electron beam moving in the electric field between two plates. (There's another one for an electron beam in fine beam tube: \frac{e}{m}=\frac{2V}{B^2r^2})
    For which experiment is that?
    Edit: the top equation?

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    (Original post by PotterPhysics)
    @Turning points people:

    Are we meant to know \frac{e}{m}=\frac{2yd}{V_pt^2} for an electron beam moving in the electric field between two plates. (There's another one for an electron beam in fine beam tube: \frac{e}{m}=\frac{2V}{B^2r^2})
    This is the one where you use s=1/2at^2 and VQ/d = ma right? And Yes, you do. It does only say you need to know one, but they can ask you any of of the four that are mentioned
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    (Original post by Mehrdad jafari)
    For which experiment is that?
    Edit: the top equation?

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    Specific charge determination
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    (Original post by Protoxylic)
    Specific charge determination
    Was it for Thomson's observations?


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