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AQA Physics PHYA5 - 28th June 2016 [Exam Discussion Thread] Watch

1. Predictions on 6 marker for section A and the Applied Physics section?
2. (Original post by Ainsleyy)
Bump
I'm not sure if that has been answered already because my page won't refresh but here's my answer and the notes we got given for it won't upload for some reason but if you want them pm me and ill find a way
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3. (Original post by Ainsleyy)
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First you need to find the difference between the absolute magnitude of the two stars

Then because every +1 change in magnitude gives a x2.5 change in brightness, you need to do 2.5 raised to the power of the difference in absolute magnitude

So 2.5^9.8 which is around 8000
4. (Original post by HollyAliciaMay)
First you need to find the difference between the absolute magnitude of the two stars

Then because every +1 change in magnitude gives a x2.5 change in brightness, you need to do 2.5 raised to the power of the difference in absolute magnitude

So 2.5^9.8 which is around 8000
McDerdactyl

Ah okay thanks guys. Do you know if we have to learn
b = L/(4pi(Rsquared) or m = -2.5logb or m2 - m1 = -2.5log(b2/b1)?
They dont seem to be in the spec but they are in the book.
5. (Original post by rory58824)
Predictions on 6 marker for section A and the Applied Physics section?
Discuss the main features of a flywheel and how these features may be used in the real world.
6. (Original post by twallien)
In the June 2013 exam it asks you to work out the energy released when 4 hydrogen atoms are converted in to helium and two positrons. In the mark scheme they ignore the electron in the hydrogen atom so the mass defect is:

4 x mass_proton - mass_helium - 2xmass_electron

bump
7. wag1 mandem i have 1 day left, ive been too focused on fp2 and 3, do you think theres still time to start revision adequately on this
8. What are fission fragments and why are they unstable?
9. (Original post by ReeceFraser)
What are fission fragments and why are they unstable?
Is this from the June 14 paper, I was confused on this q too, can anyone explain this?

Also, in a nuclear reactor, when the thermal neutron undergoes fusion with the uranium, and releases a few neutrons and energy, is beta minus decay happening?
10. (Original post by ReeceFraser)
What are fission fragments and why are they unstable?
The daughter nuclei of a fissioned nucleus. They're unstable because they normally contain more neutrons than thier stable isotopes.
11. (Original post by boyyo)
Is this from the June 14 paper, I was confused on this q too, can anyone explain this?

Also, in a nuclear reactor, when the thermal neutron undergoes fusion with the uranium, and releases a few neutrons and energy, is beta minus decay happening?
I answered the previous post but i'll put some more in detail. If you look at the N vs Z graph. The ratio of N/Z is higher for larger nuclei. Now imagine that If you halve that nucleus, its ratio will basically be the same, this means its N/Z will be higher than its stable isotope (above the stable isotope). Too many neutrons result in instability, neutron rich isotopes will decay via beta minus.
12. (Original post by twallien)
I answered the previous post but i'll put some more in detail. If you look at the N vs Z graph. The ratio of N/Z is higher for larger nuclei. Now imagine that If you halve that nucleus, its ratio will basically be the same, this means its N/Z will be higher than its stable isotope (above the stable isotope). Too many neutrons result in instability, neutron rich isotopes will decay via beta minus.
Ahh ok. You see where you said the daughter nuclei has more neutrons, but the parent Nuclei absorbs thermal neutron and undergoes beta minus decay, doesn't it lose neutrons, so the daughter has less?
13. (Original post by micycle)
Could someone explain how during fission, energy is released even though new nuclei have higher binding energy per nucleon.
Not sure if this has been answered properly. You have to imagine the binding energy is the energy REQUIRED to separate the nucleus in to its constituent protons and neutrons. the higher the binding energy per nucleon, the more stable it is. Nuclei above Iron have a higher potential energy which is released when they are fissioned.
14. (Original post by Ainsleyy)
McDerdactyl

Ah okay thanks guys. Do you know if we have to learn
b = L/(4pi(Rsquared) or m = -2.5logb or m2 - m1 = -2.5log(b2/b1)?
They dont seem to be in the spec but they are in the book.
I've never heard of them and one of my teachers is an examiner so I shouldn't think so
15. (Original post by twallien)
The daughter nuclei of a fissioned nucleus. They're unstable because they normally contain more neutrons than thier stable isotopes.
They'll also have excess energy due to the massive temperatures in the reactor core, so I reckon they'd be in an excited state too
This links in to why spent fuel rods are much more hazardous than unused fuel rods, as they'll now emit beta/gamma - just in case that comes up
16. (Original post by twallien)
bump
Mate, I'm not sure what nucleuses (probs not a word) you've been looking at but the ones I've seen don't have electrons. 10/10. gr8 banter.
17. (Original post by boyyo)
Ahh ok. You see where you said the daughter nuclei has more neutrons, but the parent Nuclei absorbs thermal neutron and undergoes beta minus decay, doesn't it lose neutrons, so the daughter has less?

Okay so the question asks "With reference to Figure 1, explain why fission fragments are unstable and explain what type of radiation they are likely to emit initially"

It fully depends on the elements involved. Yes it emits neutrons but generally speaking the ratio of N/Z will still be higher than its stable isotope.

A worked example: Uranium_235 splits in to Rubidium_92 and Caesium_140 as well as 3 neutrons. N/Z for uranium is about 1.55. N/Z for Cs is 1.545. Cs_133 is the only stable isotope meaning Cs has more neutrons than its stable isotope. I'm sure there's examples where what i have said don't apply but the question asks for general terms.
18. Any expectations for Tuesday's exam part A/B(Astro)??
I'm not sure how I'm feeling about it.. Getting consecutively 100% ums' but have no faith in myself whatsoever ahah.. Anyone recommend any other relevant spec papers or old spec papers which were challenging/different?
19. Can anyone post a model answer for the 6 mark question in jun 2014 section A.
20. (Original post by ReeceFraser)
Can anyone post a model answer for the 6 mark question in jun 2014 section A.
Just did this one now!
Robots should be controlled removing radioactive isotopes to prevent harmful particles/rays penetrating body when close.
Radioactive isotope X is a gamma emitter which requires lots of shielding due to it's long range so must be transferred to a sealed lead container immediately which absorbs enough radiation that outside the container remains at background count rate. It has a small half life meaning it's activity is very high hence it's at very high temperatures so the sealed lead container must be placed in a cooling pond to reduce activity/temperature. It should be left in cooling pond until radiation falls to background radiation.
Radioactive isotope Y is an alpha emitter with a long half life so needs to be placed in a metallic container immediately. It should then be stored underground and labelled under lock and key. Storage problems would be that the metal container mustn't deteriorate as the sample will have to be enclosed for a long time due to its long half life.

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