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

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    (Original post by toddle1)
    Do we have to know how to derive the kinetic theory model? This equation:

    pV=(1/3)Nm(crms)^2
    Yeaj


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    ahh ok, better get on it then, thanks
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    (Original post by toddle1)
    ahh ok, better get on it then, thanks
    No worries! I believe it's the only equation we need to know the derivation of in the whole unit.


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    Have they ever asked a question on deriving the kinetic theory? I can't think of when they have... Probably means it's going to come up this time ;D
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    anyone doing applied physics, know any good sites or videos about the thermodynamics stuff?
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    (Original post by CD223)
    Does this help?

    

m = 5 \log \left( \dfrac{d}{10} \right) + M

    

M = m - 5 \log \left( \dfrac{d}{10} \right)

    

d = 10 \times 10^{ \left( \frac{m-M}{5} \right)}


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    Thats awesome thank you so much
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    FP2 is over, only physics and M2 left to prepare for finally! Hopefully going to get a bit of physics reading done tonight and then a full day tomorrow, fingers crossed
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    (Original post by slaven123)
    Have they ever asked a question on deriving the kinetic theory? I can't think of when they have... Probably means it's going to come up this time ;D
    Yeah I'm reckoning it might. Just remember the main stages:

    • Time between impacts with a specific wall
    • Change of momentum
    • Force = Change of momentum/time between impacts
    • Pressure = Force/Area
    • Mean square speed takes into account all three dimensions divided by N particles
    • 1/3 Root mean square speed = velocity in one direction
    • Equation falls out to be pV = 1/3 Nmc^2


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    (Original post by ZedRigby)
    Thats awesome thank you so much
    No problem!


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    Could I have help on 2cii please not really sure how to go about it? http://filestore.aqa.org.uk/subjects...1-QP-JUN12.PDF
    Thanks


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    Hi guys I don't know if any of you can help me. Its a question about the big derivation in kinetics. I don't understand why they divide by three to get between these two lines. (In the attachment) its when all the pressure expressions are added together. Is it because its a mean and there are three dimensions? Idk...

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    (Original post by CD223)
    Yeah I'm reckoning it might. Just remember the main stages:

    • Time between impacts with a specific wall
    • Change of momentum
    • Force = Change of momentum/time between impacts
    • Pressure = Force/Area
    • Mean square speed takes into account all three dimensions divided by N particles
    • 1/3 Root mean square speed = velocity in one direction
    • Equation falls out to be pV = 1/3 Nmc^2


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    That's great thanks


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    (Original post by Jimmy20002012)
    Could I have help on 2cii please not really sure how to go about it? http://filestore.aqa.org.uk/subjects...1-QP-JUN12.PDF
    Thanks


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    Does this help?

    Name:  ImageUploadedByStudent Room1434475737.403843.jpg
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Size:  67.0 KB

    There are initially 3 x 10^22 atoms of U.

    The half life of U is 4.5 x 10^9 years so there must be 1.5 x 10^22 atoms of U and 1.5 x 10^22 atoms of Pb after one half life. This is where they intersect on the graph.

    After another half life, the U curve halves again. Conversely, the Pb curve doubles. They are the mirror of one another.


    EDIT: lol, just seen its part two. Ignore me. I'll get on the case.

    ...

    Right, you know that when there are twice as many U atoms as Pb atoms, the ratio is 2:1. This means that the number of U atoms is two thirds the total number.

    So the number of U atoms is:


    

\dfrac{2}{3} \times 3.0 \times 10^{22}



= 2.0 \times 10^{22}


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    Is the role of the coolant in a nuclear reactor just to cool the fuel down?
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    (Original post by frankiejayx)
    Is the role of the coolant in a nuclear reactor just to cool the fuel down?
    Yeah it cools the reactor down by absorbing heat produced and also means that it can evaporate into steam which drives a turbine and generates electricity.


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    (Original post by CD223)
    Yeah it cools the reactor down by absorbing heat produced and also means that it can evaporate into steam which drives a turbine and generates electricity.


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    Ahhh right thanks!
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    (Original post by _Caz_)
    Hi guys I don't know if any of you can help me. Its a question about the big derivation in kinetics. I don't understand why they divide by three to get between these two lines. (In the attachment) its when all the pressure expressions are added together. Is it because its a mean and there are three dimensions? Idk...

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    Yeah, essentially, as U, V and W are equal perpendicular components of the velocity in 3D:

    Name:  ImageUploadedByStudent Room1434476710.464510.jpg
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Size:  43.2 KB


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    (Original post by frankiejayx)
    Ahhh right thanks!
    No worries


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    (Original post by CD223)
    Yeah I'm reckoning it might. Just remember the main stages:

    • Time between impacts with a specific wall
    • Change of momentum
    • Force = Change of momentum/time between impacts
    • Pressure = Force/Area
    • Mean square speed takes into account all three dimensions divided by N particles
    • 1/3 Root mean square speed = velocity in one direction
    • Equation falls out to be pV = 1/3 Nmc^2


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    I can't think of how'd they'd go about asking about it... It would be worth like a good 10 marks if they just made you do it all at once from scratch.
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    Need a bit of motivation, anyone?
 
 
 
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