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PHYA5 ~ 20th June 2013 ~ A2 Physics

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Original post by Jack93o
I thought I done worse in unit 4, but because the grade boundaries are lower for it, then that just probably means I've done about the same as this paper :s-smilie:, and I done the EMPA

I just realised I messed up a bit more in that 6 marker, i mentioned that if the count rate was still registering after 20cm, then gamma is definitely present, which is not exactly correct, because beta radiation has a range of 'several metres' apparently

oh dear, the more I think about this paper, the more holes I can find in my answers. You know, I was actually feeling quite good right after the exam, thought I got 120/120, now I'm seeing more and more marks lost.......FUUUAAAAAARRRRKK :zomg:


I walked out of U4 upset in Jan thinking i didnt get the A* but ended up with a high A*... the grade boundaries for U4 tend to be super low


Dont even talk about marks lost, i messed this paper up niiiicely :wink: THANKS FOR HAVING HIGH GRADE BOUNDARIES ASTRO
Reply 1841
Avatar for sam1w2e
sam1w2e
8
Original post by Jack93o
for that last question in astrophysics, I didn't convert hubble's constant

but I wrote down:

time = distance/speed

time = distance/hubble's constant*distance

therefore: time = 1/hubble's constant

reckon I get at least one method mark?


Yeah I reckon you'd get a method mark for that :smile:
Reply 1842
Avatar for George_
George_
2
Original post by Jack93o
for that last question in astrophysics, I didn't convert hubble's constant

but I wrote down:

time = distance/speed

time = distance/hubble's constant*distance

therefore: time = 1/hubble's constant

reckon I get at least one method mark?


Omg I did that too! I knew it was wrong though. Did you get something like 0.0139 s Mpc km^-1??
Original post by George_
Omg I did that too! I knew it was wrong though. Did you get something like 0.0139 s Mpc km^-1??


yup, I even wrote the answer as 13.9 billion years in the hope that this would be right
I'm pretty sure it was 13.6 billion years
Reply 1845
Avatar for Matt III
Matt III
I did say i'd use the lens as an objective (stupidly) lol


I thought this is correct? Magnification of the telescope is (Focal length of objective)/(Focal length of eyepiece)? Right? So you would need a mahoosive telescope to get any kind of magnification with a 50cm eyepiece focal length?
(edited 10 years ago)
Original post by Matt III
I thought this is correct? Magnification of the telescope is (Focal length of objective)/(Focal length of eyepiece)? Right? So you would need a mahoosive telescope to get any kind of magnification with a 50cm eyepiece focal length?


thats what I put! i said if it was the eyepeice and you wanted a magnification of say, 10 x, the telescope would be over 5 metres
Reply 1847
Avatar for MSI_10
MSI_10
15
Original post by Jack93o
whats the consensus for section A? harder/easier than the previous papers?

also for those who done astrophysics, same question to you as well

oh yeah, for that last question for astrophysics, I didn't convert the hubble's constant, so I just put: 1/H

I got 0.00... something, but the weird thing is that you get the actual number (in terms of billions of years) in that decimal number, whats the relationship excactly?


Hardest section A out of all of then in my opinion :/

What did ppl put for why star needs high temperature for fusion? I said T increases as t is proportional to ke and fusion needs a lot of energy to happen but realised after t being proportional to energy is only for ideal gases :/

Posted from TSR Mobile
Reply 1848
Avatar for MSI_10
MSI_10
15
Original post by TerminatorFive
thats what I put! i said if it was the eyepeice and you wanted a magnification of say, 10 x, the telescope would be over 5 metres


So was the answer objective? :s-smilie:

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Reply 1849
Avatar for Matt III
Matt III
So was the answer objective?

It's what all my friends and I put
Reply 1850
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MSI_10
15
Original post by Matt III
It's what all my friends and I put


Same but even mix of ppl put eyepiece

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Original post by MSI_10
So was the answer objective? :s-smilie:

Posted from TSR Mobile


I was certain it was, but then I came home and came on here, and most people thought otherwise :P
Original post by MSI_10
Hardest section A out of all of then in my opinion :/

What did ppl put for why star needs high temperature for fusion? I said T increases as t is proportional to ke and fusion needs a lot of energy to happen but realised after t being proportional to energy is only for ideal gases :/

Posted from TSR Mobile


It's not necessarily just true for ideal gases. The hotter something is, the more internal energy it has, the faster its molecules move. In a sense, thermal energy is just kinetic and potential energy at the molecular level (and vice versa)
Original post by George_
Omg I did that too! I knew it was wrong though. Did you get something like 0.0139 s Mpc km^-1??


I WROTE THAT AS MY UNIT DO I GET A MARK IF I DIDNT CONVERT from that small number to years?!
Original post by Matt III
I thought this is correct? Magnification of the telescope is (Focal length of objective)/(Focal length of eyepiece)? Right? So you would need a mahoosive telescope to get any kind of magnification with a 50cm eyepiece focal length?



I will love you forever if this is right...that was my logic! AHHHH (thanks for the quote :wink:)
Original post by TerminatorFive
I was certain it was, but then I came home and came on here, and most people thought otherwise :P


I can't help but feel that this might be a question where you'd get credit for either answer providing you have a decent explanation of your reasoning. I thought that, ideally, the focal length for the eyepiece lens should be as short as possible, and that 48cm is not the shortest possible.

I know it's totally irrelevant, but look here:
https://en.wikipedia.org/wiki/Eyepiece#Focal_length

This says that the typical eyepiece lens for a refractive telescope ranges from about 3-50mm

so 48cm would be very long by this standard.

And, after all, why have a 0.5m lens that requires a 50m telescope for 100x magnification when you could have a 5mm lens that only requires a 0.5m telescope?
Original post by MSI_10
Hardest section A out of all of then in my opinion :/

What did ppl put for why star needs high temperature for fusion? I said T increases as t is proportional to ke and fusion needs a lot of energy to happen but realised after t being proportional to energy is only for ideal gases :/

Posted from TSR Mobile


I didn't write all that, I basically just said, it needs a high temperature so that the nuclei move with enough kinetic energy to overcome the electrostatic repulsion

I more or less implied (without saying why) that higher temperature = faster movement/higher kinetic energy, I hope thats okay

I mean, its common sense, right? its a given that higher temperature would cause the nuclei to move faster, after all, temperature is merely the result of stuff (molecules/ atoms/nuclei/particles) moving about
Original post by MSI_10
1.36 x 10^10 years?

And what did yous put for whether or not refracting telescope is obj or eyepiece? Think I'm the only one who put objective :\


i put objective!! i dont know how we are supposed to know what the longer focal length would be so i hoped they would accept either as long as the reasoning was right...probs wont happen knowing aqa though...
Original post by bugsuper
I can't help but feel that this might be a question where you'd get credit for either answer providing you have a decent explanation of your reasoning. I thought that, ideally, the focal length for the eyepiece lens should be as short as possible, and that 48cm is not the shortest possible.

I know it's totally irrelevant, but look here:
https://en.wikipedia.org/wiki/Eyepiece#Focal_length

This says that the typical eyepiece lens for a refractive telescope ranges from about 3-50mm

so 48cm would be very long by this standard.

And, after all, why have a 0.5m lens that requires a 50m telescope for 100x magnification when you could have a 5mm lens that only requires a 0.5m telescope?


Ahh nice one, im feeling more confident now, hopefully it will be based on explanation rather than merit, cause in theory you could build any sized telescope, it might just be impractical!
Original post by TerminatorFive
Ahh nice one, im feeling more confident now, hopefully it will be based on explanation rather than merit, cause in theory you could build any sized telescope, it might just be impractical!


Indeed. If the focal length was a few mm, we'd have less of a case, as that would clearly be an eyepiece, but I think there's a bit of ambiguity

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