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

1. (Original post by CD223)
I see. So those with lower mass will have greater velocity and hence a greater share of the total energy, as it depends on v^2?

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exactly
2. Could anyone explain what we need to know of the parallax angle?
3. (Original post by CD223)
*
Thanks CD223. I understand how to get the answer once you know that d=1/p, it's just I had never seen that before anywhere, neither in the textbook nor spec notes online. At least I'll know it now if it comes up tomorrow.

P.s Cheers for your notes in the op, was useful to have a quick read through as there's little bits in the Nelson Thornes book not covered in the CGP one
4. (Original post by you-only-live-once)
anyone doing medical option?
Yeah I am it's annoying, every past paper has some different facts which you needed to know, most of which aren't in my textbook or notes -.- just going through loads of old-spec medical papers at the moment...
5. http://filestore.aqa.org.uk/subjects...1-QP-JUN14.PDF

hey guys can anyone explain why the markscheme doesnt take the binding energy of neutrons into account in Q 1b (ii) ? confused
6. (Original post by Star Light)
Yeah I am it's annoying, every past paper has some different facts which you needed to know, most of which aren't in my textbook or notes -.- just going through loads of old-spec medical papers at the moment...
Yes i know! what do you think will be the 6 marker?
7. (Original post by CD223)

This equation relates the maximum distance, d, measurable (the precision) of a telescope to the parallax angle it is capable of resolving, p.

Subbing in the numbers gives:

As it asks for the distance in metres,

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this d = 1/p business.. It's not in formula book ? Where can I find notes on it or how they got the equation (derive)
8. d=1/p isn't on the spec anymore?
9. (Original post by johnh545)
I need help with this question.
i dont really understand what it means by 1 in 400 detected on the facing surface of the detector.
were told earlier in the question that the detector has area 1.5x10^-3 and the count rate is 0.62
Anyone?
10. (Original post by 000alex)
d=1/p isn't on the spec anymore?
I agree.

I did it a different way but you can get 1.55 which is approximately 2 (their answer 1 s.f since they say so) or you can get 3 depending on the question I ask in this diagram:

11. (Original post by frankiejayx)
Could anyone explain what we need to know of the parallax angle?
The parallax angle is half the angular shift in the line of sight over six months drawn directly from Earth to the object of interest.

The angular separation to an object is measured over 6 months when the earth has rotated about its axis and measurements are taken from diametrically opposite positions on earth.

Nearby stars appear to move against the backdrop of more distant stars, allowing this angular separation to be measured.

Once you have the angular separation, astronomers halve this number to get the parallax angle.

The formula

Can then be used. By subbing in your value of p you can determine the distance to the object in parsecs

http://www2.jpl.nasa.gov/teachers/at.../parallax.html

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12. (Original post by Master Sam)
http://filestore.aqa.org.uk/subjects...1-QP-JUN14.PDF

hey guys can anyone explain why the markscheme doesnt take the binding energy of neutrons into account in Q 1b (ii) ? confused

Are the neutrons bounded to anything? They are just neutrons so they have a binding energy of zero
13. What's the point of the 97% U-238 in fuel rods if it's not fissionable?
14. (Original post by EconFan_73)
Thanks CD223. I understand how to get the answer once you know that d=1/p, it's just I had never seen that before anywhere, neither in the textbook nor spec notes online. At least I'll know it now if it comes up tomorrow.

P.s Cheers for your notes in the op, was useful to have a quick read through as there's little bits in the Nelson Thornes book not covered in the CGP one

(Original post by betbi3etwerrd)
this d = 1/p business.. It's not in formula book ? Where can I find notes on it or how they got the equation (derive)

(Original post by 000alex)
d=1/p isn't on the spec anymore?
Nope. It's not in the formulae sheet. You're expected to remember it, as evidenced by last year's question.

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15. Does anyone have a way to remember the order of star types/spectral classes or whatever on a Hertzsprung - Russell diagram?
16. (Original post by mrno1324)
What's the point of the 97% U-238 in fuel rods if it's not fissionable?
Natural uranium is not found in the more-fissionable form of U-235 directly. U-238 fuel has to be enriched with U-235 to obtain a fissionable fuel.

It's extremely difficult to get a fuel with a higher % of U-235. I also imagine it would be fairly dangerous as the reaction could spiral out of control if more fissionable material was used.

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17. (Original post by Plasmapause)
Does anyone have a way to remember the order of star types/spectral classes or whatever on a Hertzsprung - Russell diagram?
Oh
Be
A
Fine
Girl/Guy
Kiss
Me

I use that for the order haha!

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18. (Original post by CD223)
The parallax angle is half the angular shift in the line of sight over six months drawn directly from Earth to the object of interest.

Can then be used. By subbing in your value of p you can determine the distance to the object in parsecs

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Thanks
19. (Original post by CD223)
Oh
Be
A
Fine
Girl/Guy
Kiss
Me

I use that for the order haha!

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Thank you!
20. 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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