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

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Reply 760
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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Reply 761
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.
Reply 762
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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Reply 763
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?
Reply 764
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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Reply 765
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?
Reply 766
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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Reply 767
Can anyone who does Astro explain the derivation or meaning or both for the following apparent magnitude equation:

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

I've only seen the mM=5log(d10)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
Reply 769
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=FAP=\frac{F}{A} and therefore:

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

P×V=FL=W\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×DistanceWork = Force \times Distance


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Reply 770
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
Reply 771
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:

α\alpha: Smoke detectors

β\beta: Paper thickness

γ\gamma: Medical tracers

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


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Reply 772
Original post by CD223
I would just say that you should be aware of suitable applications for each type:

α\alpha: Smoke detectors

β\beta: Paper thickness

γ\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? :colondollar:
Reply 773
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(Io)m=-2.5log({{I}_{o}}) I've only seen the mM=5log(d10)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!
Reply 774
Original post by JJBinn
Thanks, do you have a small explanation for each by any chance? :colondollar:


No worries!

α\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.

β\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.

γ\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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Reply 775
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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Reply 776
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 :/
Reply 777
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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Reply 778
Original post by CD223
No worries!

α\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.

β\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.

γ\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
Anyone know any other disadvantages of a CCD other than expensive and need to be kept cool?

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