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

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    (Original post by Lau14)
    Yeah it's not the easiest to get your head around sometimes!Magnitude is just a logarithmic scale, although I guess not the nicest one!
    Do you have any tips for remembering the absorption spectra for stellar classes? I've no clue tbh. All I know is that the Balmer lines are prominent in O, B and A.

    I've otherwise remembered the colour and temperature differences.


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    (Original post by CD223)
    Do you have any tips for remembering the absorption spectra for stellar classes? I've no clue tbh. All I know is that the Balmer lines are prominent in O, B and A.

    I've otherwise remembered the colour and temperature differences.


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    No sorry, I just memorise them the boring way :/ That is the hardest column though, at least colour and temperature have a bit of a pattern/follow on from each other nicely.
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    (Original post by Lau14)
    No sorry, I just memorise them the boring way :/ That is the hardest column though, at least colour and temperature have a bit of a pattern/follow on from each other nicely.
    Yeah:

    From memory I fall down from A onwards.

    O is H, H+ and He
    B is H (Balmer), He
    A is H (strongest), ionised metals
    F is Ionised Metals (Fe+, Ca+)
    G is Ionised and Neutral Metals
    K is Neutral atoms, TiO

    (I just had to look up F, G and K lol)

    Is K the only type of star with "molecular bands"?


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    (Original post by CD223)
    Yeah:

    From memory I fall down from A onwards.

    O is H, H+ and He
    B is H (Balmer), He
    A is H (strongest), ionised metals
    F is Ionised Metals (Fe+, Ca+)
    G is Ionised and Neutral Metals
    K is Neutral atoms, TiO

    (I just had to look up F, G and K lol)

    Is K the only type of star with "molecular bands"?


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    Yeah I struggle with the middle mostly, I can remember the bottom a bit

    Can't say I've heard that term before?
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    (Original post by Lau14)
    Yeah I struggle with the middle mostly, I can remember the bottom a bit

    Can't say I've heard that term before?
    Just realised I missed out M. How on earth am I going to pass this exam.

    It was in a past paper I did on the HR diagram where you had to indicate a point on the diagram that would be likely to have molecular bands - it was actually an M class star, sorry for the confusion - I presume due to the prominence of the molecule of TiO.


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    (Original post by CD223)
    Just realised I missed out M. How on earth am I going to pass this exam.

    It was in a past paper I did on the HR diagram where you had to indicate a point on the diagram that would be likely to have molecular bands - it was actually an M class star, sorry for the confusion - I presume due to the prominence of the molecule of TiO.


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    And I didn't even notice... well we're doing well :P

    My guess would be it just means spectra due to molecules then, because TiO is the only molecule on the list, but I don't actually know?
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    (Original post by Lau14)
    And I didn't even notice... well we're doing well :P

    My guess would be it just means spectra due to molecules then, because TiO is the only molecule on the list, but I don't actually know?
    Yeah I was stumped by that question.

    I'm so worried for physics. I'm nowhere near at the level as I am with other subjects:/


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    Can anyone who does Astro explain the derivation or meaning or both for the following apparent magnitude equation:

    m=-2.5log({{I}_{o}})

    I've only seen the m-M=5log(\frac{d}{10}) version before.

    Where does the first equation appear, as it's not on the formulae sheet?


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    Do we need to know that work done is pressure x volume? Came across it in an old paper
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    (Original post by noseypo)
    Do we need to know that work done is pressure x volume? Came across it in an old paper
    Erm, I suppose it could be derived from the fact that P=\frac{F}{A} and therefore:

    \rightarrow P \times V =\frac{FV}{A}

    \rightarrow P \times V = FL = W

    Where P is the pressure, V is the volume, A is the cross sectional area, L is the length, F is the force, W is the work done.

    I guess it just drops out of
    Work = Force \times Distance


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    Does anybody know how much we need to know about the uses of radioactive isotopes? There's a small section in the textbook but even the summary questions are more about calculations. I don't fancy learning them for nothing, my brain is at the stage where I feel like I've learnt so much that anymore info is too much haha
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    (Original post by JJBinn)
    Does anybody know how much we need to know about the uses of radioactive isotopes? There's a small section in the textbook but even the summary questions are more about calculations. I don't fancy learning them for nothing, my brain is at the stage where I feel like I've learnt so much that anymore info is too much haha
    I would just say that you should be aware of suitable applications for each type:

    \alpha: Smoke detectors

    \beta: Paper thickness

    \gamma: Medical tracers

    Be prepared to comment on the reason behind their use, quoting relative penetrating power, ionisation, mass etc.


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    (Original post by CD223)
    I would just say that you should be aware of suitable applications for each type:

    \alpha: Smoke detectors

    \beta: Paper thickness

    \gamma: Medical tracers

    Be prepared to comment on the reason behind their use, quoting relative penetrating power, ionisation, mass etc.


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    Thanks, do you have a small explanation for each by any chance?
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    (Original post by JJBinn)
    Does anybody know how much we need to know about the uses of radioactive isotopes? There's a small section in the textbook but even the summary questions are more about calculations. I don't fancy learning them for nothing, my brain is at the stage where I feel like I've learnt so much that anymore info is too much haha
    I think you should know an example use for each type of radiation and how it works, but as far as I know nothing further (eg. alpha is used in smoke detectors, beta in paper thickness monitoring, gamma to sterilise medical equipment).

    (Original post by CD223)
    Yeah I was stumped by that question. I'm so worried for physics. I'm nowhere near at the level as I am with other subjects:/ Posted from TSR Mobile
    (Original post by CD223)
    Can anyone who does Astro explain the derivation or meaning or both for the following apparent magnitude equation: m=-2.5log({{I}_{o}}) I've only seen the m-M=5log(\frac{d}{10}) version before. Where does the first equation appear, as it's not on the formulae sheet? Posted from TSR Mobile
    I've never seen that formula before, and it isn't in the specification (or the formula sheet, as you said), so I wouldn't think we need to know it.

    I've definitely got a lot of revision to do!
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    (Original post by JJBinn)
    Thanks, do you have a small explanation for each by any chance?
    No worries!

    \alpha: Smoke detectors because a steady stream of alpha particles pass between two conducting plates, creating an ionisation current that allows a circuit to flow, due to its large mass meaning atoms between the plates are ionised and a current flows. When smoke interrupts this stream, the current drops (or is completely removed) and an alarm sounds.

    \beta: Paper thickness Beta isn't stopped by paper like alpha is. Beta can pass through a continuous sheet of paper through to a detector on the other side of the paper. The count rate should be steady. If the paper is too thick, the count rate falls below the tolerance levels and the paper presses are clamped together tighter to make it thinner and allow more particles to pass through the paper. The opposite happens if the paper is too thin and the count rate too high.

    \gamma: Medical tracers Gamma is most penetrative and so when a patient swallows or injects a radioactive tracer into their body, gamma ray beams may pass through the body but be absorbed by tracers near the affected area, allowing a concentration on a certain area of the body for doctors to use when diagnosing conditions. Other radiation cannot pass through the body from the outside of the body.



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    (Original post by Lau14)
    I think you should know an example use for each type of radiation and how it works, but as far as I know nothing further (eg. alpha is used in smoke detectors, beta in paper thickness monitoring, gamma to sterilise medical equipment).




    I've never seen that formula before, and it isn't in the specification (or the formula sheet, as you said), so I wouldn't think we need to know it.

    I've definitely got a lot of revision to do!
    It's in the CGP guide I believe? It worries me because it isn't on the formula book or the spec. Apparently the spec mentions that we need to be aware of the "link between apparent magnitude and intensity" though, which suggests knowledge of that equation?


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    (Original post by CD223)
    It's in the CGP guide I believe? It worries me because it isn't on the formula book or the spec. Apparently the spec mentions that we need to be aware of the "link between apparent magnitude and intensity" though, which suggests knowledge of that equation?


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    Possibly? Just hope it doesn't come up now :/
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    (Original post by Lau14)
    Possibly? Just hope it doesn't come up now :/
    Hmm. I may just learn it anyway. Can't do any harm.


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    (Original post by CD223)
    No worries!

    \alpha: Smoke detectors because a steady stream of alpha particles pass between two conducting plates, creating an ionisation current that allows a circuit to flow, due to its large mass meaning atoms between the plates are ionised and a current flows. When smoke interrupts this stream, the current drops (or is completely removed) and an alarm sounds.

    \beta: Paper thickness Beta isn't stopped by paper like alpha is. Beta can pass through a continuous sheet of paper through to a detector on the other side of the paper. The count rate should be steady. If the paper is too thick, the count rate falls below the tolerance levels and the paper presses are clamped together tighter to make it thinner and allow more particles to pass through the paper. The opposite happens if the paper is too thin and the count rate too high.

    \gamma: Medical tracers Gamma is most penetrative and so when a patient swallows or injects a radioactive tracer into their body, gamma ray beams may pass through the body but be absorbed by tracers near the affected area, allowing a concentration on a certain area of the body for doctors to use when diagnosing conditions. Other radiation cannot pass through the body from the outside of the body.



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    Thanks again, these are perfect
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    Anyone know any other disadvantages of a CCD other than expensive and need to be kept cool?
 
 
 
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