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

1. The corrected count rate just means the count rate after you take away background radiation.

You can find activity either using the radioactive decay eqn or a= lambda x N
2. (Original post by AQATrolledMe)
Yea we do, isnt it just p = m/v
It's (for an ideal gas of molar mass M): (Pressure x Molar Mass)/(Gas constant * Temperature)
3. (Original post by ChillGod)
You have to take into account the mass of electrons on the left hand side. There's the same amount of electrons as protons.
Yeah but that has no effect since they are the same on each side they cancel out
4. (Original post by philo-jitsu)
I have been doing that, well I just use 931.5 to find MeV but I am still getting the mass defect wrong...

Its number 14 on this

https://e4cf8bb391554b7c9d8e0fc42269...r%20Energy.pdf
No you have to use 1.661 x 10^-27 instead of 931. 931 is to find binding energy.
5. Can someone define parallax?
6. Do we need to know how to work out nuclear diameter, Sin(theta) = 1.22lamda/d, as it isnt in the specification but is in the book.
7. 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

8. (Original post by ReeceFraser)
Do we need to know how to work out nuclear diameter, Sin(theta) = 1.22lamda/d, as it isnt in the specification but is in the book.
It came up in a 6 marker for one of the recent exams. Explain the difference between Rutherfords experiment and electron defraction and provide equations...
9. How exactly do Supernovae show that the expansion of the universe is accelerating. I understand that they are dimmer than expected using calculations with constant expansion but how does this lower brightness show that expansion is accelerating?
10. Guys how is the ideal gas equation a thing when each individual equation that's combined has it's own rules.
For example: Pressure is inversely proportional to volume at constant temperature. Then pressure is directly proportional to temperature when volume is constant.
How can you combine these things when the conditions aren't the same for each equation. The Pressure law states that volume is constant and Boyles law states that temperature is constant. There are different conditions because volume isn't constant for Boyles law.
I don't get how you can combine them if they aren't true for each others conditions. Can anyone help?
11. (Original post by Vikingninja)
How exactly do Supernovae show that the expansion of the universe is accelerating. I understand that they are dimmer than expected using calculations with constant expansion but how does this lower brightness show that expansion is accelerating?
Isn't it something to do with redshift and blueshift??
12. Is anyone else hopeless with radioactivity and nuclear physics? I missed 3 lessons and i feel like i missed the whole course
13. (Original post by McDerdactyl)
Isn't it something to do with redshift and blueshift??
No its the brightness of the supernovae detected.
14. (Original post by Squishy•)
Guys how is the ideal gas equation a thing when each individual equation that's combined has it's own rules.
For example: Pressure is inversely proportional to volume at constant temperature. Then pressure is directly proportional to temperature when volume is constant.
How can you combine these things when the conditions aren't the same for each equation. The Pressure law states that volume is constant and Boyles law states that temperature is constant. There are different conditions because volume isn't constant for Boyles law.
I don't get how you can combine them if they aren't true for each others conditions. Can anyone help?
1- pressure inversely proportional to volume so PV = constant.
2- Pressure directly proportional to temperature so P= constant x T
3- PV = constant and P/T = constant. Hence PV/T = constant where the constant = nR. Therefore PV/T = nR, PV =nRT.
15. (Original post by Franckenstar)
1- pressure inversely proportional to volume so PV = constant.
2- Pressure directly proportional to temperature so P= constant x T
3- PV = constant and P/T = constant. Hence PV/T = constant where the constant = nR. Therefore PV/T = nR, PV =nRT.
But the thing is isn't pressure only proportional to temperature when it's constant volume and for Boyles law it isn't constant volume so how is can you combine them?
16. Could someone explain how during fission, energy is released even though new nuclei have higher binding energy per nucleon.
17. ASTROPHYSICS 2015 PAPER Q1.a
Could someone explain why they have added 1 to the AU unit??
Attachment 556909556911
Attached Images

18. (Original post by Squishy•)
But the thing is isn't pressure only proportional to temperature when it's constant volume and for Boyles law it isn't constant volume so how is can you combine them?
V= constant x T
P= constant x T so
PV= constant x T
19. (Original post by micycle)
Could someone explain how during fission, energy is released even though new nuclei have higher binding energy per nucleon.
Conservation of Energy

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20. (Original post by arrow_h)
ASTROPHYSICS 2015 PAPER Q1.a
Could someone explain why they have added 1 to the AU unit??
Attachment 556909556911
An astronomical unit is the distance between the earth and the sun. The table tells you the max distance between the sun and vesta. So the furthest vesta can be from the earth is the furthest it can be from the sun + the distance between the earth and the sun which is 1 AU.

2.57 + 1

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