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

1. (Original post by _Caz_)
Tbh CD223 deserves a medal. What ever grades you all get, it is because of CD223 answering all your queries.

Respect.

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Thanks Caz - I don't do it for the medals really

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2. (Original post by mrno1324)
What's the point of the 97% U-238 in fuel rods if it's not fissionable?
If you had pure U235 in a clump at critical mass that's what is colloquially known as a nuclear bomb
3. Why is it that the doppler effect never come up?
4. you only need 3% u235 becuase otherwise **** would get nasty.
5. Could anyone explain the twin paradox doing turning points?

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6. How can you work out which star is closer to the Earth given absolut & apparent magnitude and temperature?
7. (Original post by Jimmy20002012)
Could anyone explain the twin paradox doing turning points?

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We don't need to know it just that time goes slower for the moving object

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8. How I did the question:

9. Has anyone got any tips on energy (heat specifically) transfer questions? I always seen equations in the mark scheme along the lines of: Heat supplied by X = Heat gain by mateiral Y + heat dissipated by Z. But I struggle forming these equations.
10. (Original post by Protoxylic)
Are the neutrons bounded to anything? They are just neutrons so they have a binding energy of zero
cheers
11. (Original post by EconFan_73)
Anyone know how to do 4b on last year's Astrophysics paper?

Basically says distance to stars measured using angle of parallax method to a precision of 0.002 arc seconds. Calculate the maximum distance measurable?

Mark scheme shows use of d=1/p....?
distance is 1/angle in arc seconds. so 1/0.02 gives 500 parsecs, which you convert to meters.
12. (Original post by johnh545)
Anyone?
Basically what this means is that for every 400 emitted rays the detecter only detects 1 of them. For example if the source emitted 800, the detector would detect 2.
13. for the equation r = r0 A1/3 is r0 always 1.4 x 10-15 m or will they give you a value depending on the question in the exam?
14. hey can anyone explain question 3b(i) on this paper...

http://filestore.aqa.org.uk/subjects...1-QP-JUN12.PDF

i don't understand why they are using area of a sphere and why the radius of that sphere is then 0.18
15. What is r0 in the nuclear equation? Book says 1.05 fm but wiki says 1.25fm...
16. What do we want the 6 marker to be tomorrow?

And does anyone have a link to a good set of Applied notes?
17. (Original post by Disney0702)
for the equation r = r0 A1/3 is r0 always 1.4 x 10-15 or will they give you a value depending on the question in the exam?
I just asked that a few seconds after you!

book says 1.05fm, do they give you a value in the exams?

18. Attachment 430659430667

Why is the mass of hydrogen 1.00728?
Attached Images

19. (Original post by ubisoft)
I just asked that a few seconds after you!

book says 1.05fm, do they give you a value in the exams?
(Original post by Disney0702)
for the equationr = r0 A1/3 is r0 always 1.4 x 10-15 m or will they give you a value depending on the question in the exam?
I don't think we're expected to know a value, we'll be given one/given information to calculate it in the exam I think.
20. Hey can anyone explain why you multiply by 0.5 for question 4(a)(i)
http://filestore.aqa.org.uk/subjects...C-QP-JUN12.PDF

Thanks

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