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

1. (Original post by donutellme)
Attachment 430659

Attachment 430659430667

Why is the mass of hydrogen 1.00728?
That Hydrogen only contains 1 proton so it's just the mass of a proton.

If you remember the binding energy graph and look at where 1 nucleon is, it's approximately 0 so binding energy of the atom is approximately zero -> just the mass of a proton.
2. (Original post by Lau14)
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.
Ah okay thank you
3. (Original post by betbi3etwerrd)
That Hydrogen only contains 1 proton so it's just the mass of a proton.

If you remember the binding energy graph and look at where 1 nucleon is, it's approximately 0 so binding energy of the atom is approximately zero -> just the mass of a proton.
Yeah, but wouldn't that just be 1au?
4. (Original post by johnh545)
Anyone?
Theres more than 1 way to do this calculation however i think the easiest way to look at it is if the detector counts 0.62/s but this is only 1/400 of the photons emitted. So if the detector was on the source the count rate would be 248/s (0.62 x 400) this is the activity of the source however only a small part of it as the area of the detector is 1.5x10^-3 and the rays are emitted uniformly in all directions. The total activity of the source is how many emitted per second. As worked out in b(i) you know the ratio of the area of dectector to area of emitted rays. So use 248 ÷ this (3.684x10^-3) and you get 67000 Bq
5. How do you work out the corrected count rate?
6. (Original post by donutellme)
Yeah, but wouldn't that just be 1au?
In this case it's just one proton so you just look at the mass of a proton from a your formula book and it gives it in u.

Definition of au is 1/12 th of the mass of a carbon atom.
7. Would we need to know the experimental details of Boyles, Pressure law, Charles law. Not sure if they would ask something like draw a diagram with the apparatus to find out the relationship between ... pressure and temp etc
8. (Original post by DannySmith420)
Theres more than 1 way to do this calculation however i think the easiest way to look at it is if the detector counts 0.62/s but this is only 1/400 of the photons emitted. So if the detector was on the source the count rate would be 248/s (0.62 x 400) this is the activity of the source however only a small part of it as the area of the detector is 1.5x10^-3 and the rays are emitted uniformly in all directions. The total activity of the source is how many emitted per second. As worked out in b(i) you know the ratio of the area of dectector to area of emitted rays. So use 248 ÷ this (3.684x10^-3) and you get 67000 Bq
ok, but what would be the point of a detector only detecting 1 in 400 photons that hit it?
9. (Original post by johnh545)
ok, but what would be the point of a detector only detecting 1 in 400 photons that hit it?
I'm guessing you can't get detectors that are 100% efficient.
10. June 14 is a godsend. You can drop 17 marks and still get full UMS. Praying we have similar grade boundaries for tomorrow!
11. (Original post by slaven123)
June 14 is a godsend. You can drop 17 marks and still get full UMS. Praying we have similar grade boundaries for tomorrow!
they tend to all have fairly low boundaries,
more often than not anyway.
12. Could someone explain the signficance of abundance of hydrogen and helium in ration 3:1 as evidence of a hot big bang?
13. Just wondering, do we need to know how a black hole is formed?

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14. (Original post by johnh545)
they tend to all have fairly low boundaries,
more often than not anyway.
Only the past two years have been properly low! But yeah, they are generally pretty nice for unit 5
15. (Original post by JaySP)
Could someone explain the signficance of abundance of hydrogen and helium in ration 3:1 as evidence of a hot big bang?
at one point universe was like the star core, and fused hydrogen to helium meaning it was very hot and dense
16. 6 marker predictions for astro and nuclear?
17. (Original post by xela238)
Just wondering, do we need to know how a black hole is formed?
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Just that it's created at the end of the lifecycle of a star whose core is more than 3 times the sun's mass.
This means that the neutrons can't withstand the gravitational forces and so it collapses to an infinitely dense point. This is the blackhole.
18. I believe we will be getting the R paper because I just heard that the AQA Biology students got an R paper
19. Someone give me a breakdown on how I should give S.F in questions which they have not asked for appropriate number of S.F

20. Always get stuck on these sorts of questions, can someone give me a hand please

EDIT - just realised I can equate kinetic energy and eV

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