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# The Physics PHYA2 thread! 5th June 2013 Watch

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1. (Original post by x-Sophie-x)
Ah no. It wasn't in the video.

I just want to clarify, does TIR only happen when the ray moves from a more refractive substance to a less refractive substance? OR when the critical angle is larger the the incident ray?

Or does both have to be true?
Your first point is correct! For second point is the other way around . So, the incident angle must be bigger than the critical angle for TIR to occur.
2. could someone please help me on June 2011 paper question 5d, I've looked at mark-scheme but still quite confused.

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3. (Original post by StalkeR47)
Your first point is correct! For second point is the other way around . So, the incident angle must be bigger than the critical angle for TIR to occur.
could someone please help me on June 2011 paper question 5d, I've looked at mark-scheme but still quite confused.

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you have a right angled triangle, so 180-(90+80)=10, so this can be used with snell's law to get the angle thea
5. (Original post by StalkeR47)
Your first point is correct! For second point is the other way around . So, the incident angle must be bigger than the critical angle for TIR to occur.
Oh yeah haha :L

Do both have to be true, or can either of them allow TIR to occur?
6. (Original post by x-Sophie-x)
Oh yeah haha :L

Do both have to be true, or can either of them allow TIR to occur?
Just one can be true for TIR to occur.
7. (Original post by masryboy94)
its constant but for single slit it decreases
Thank you so much! And for the diffraction grating?
So the graph of intensity/distance

Double Slit: fringes of the same width and the same intensity.
Single Slit: central fringe double the width of other fringes and intensity decreases.

Thank you!
8. (Original post by Raimonduo)
x
(Original post by DannyyP)
x
Is my understanding of angles correct in this diagram?
Where green is refracted and theta is incidence and red is crit angle?
9. (Original post by StalkeR47)
Just one can be true for TIR to occur.
How, for TIR both have to be true?
10. (Original post by Qari)
Oh sorry, did not realise. HAHA. Felling confident for the exam. But, it could go awfully bad if I see a vague question. WBU?
11. (Original post by StalkeR47)
Just one can be true for TIR to occur.
no both HAVE to true !
12. (Original post by Qari)
TIR is when ray moves from more refractive to less refractive and the incident ray has to be greater than crictical angle
Thanks

That's what I meant! >.<
13. (Original post by StalkeR47)
Oh sorry, did not realise. HAHA. Felling confident for the exam. But, it could go awfully bad if I see a vague question. WBU?
Worried over 6 marker, and question about how horizontal force can decrease or increase
14. (Original post by masryboy94)
no both HAVE to true !
Could you tell us how to derive fringe width?
15. (Original post by Qari)
How, for TIR both have to be true?
No, just 1 is sufficient. There was a question in the exam, 1 was true and the other was not and the mark scheme said TIR should occur. So that is how I know.
16. (Original post by NabRoh)
Is my understanding of angles correct in this diagram?
Where green is refracted and theta is incidence and red is crit angle?
Yes, then you can use snell's law to work out theta
17. (Original post by masryboy94)
no both HAVE to true !
Ta
18. (Original post by NabRoh)
Is my understanding of angles correct in this diagram?
Where green is refracted and theta is incidence and red is crit angle?
Different to what I would have done, but still correct.
19. (Original post by StalkeR47)
Here you go m8!
OMG Thank you soooooooo much!! Ur so ace!!
20. (Original post by Bixel)
Hey guys,
Do we actually need to know all the mathematics and proof behind single slit diffraction and diffraction grating? I can't get my head round it, and it seems quite a lot for AS.

By derivation, I mean this:
http://www.antonine-education.co.uk/...n_of_young.htm
Has anyone got any idea for this? It'd be great if someone could enlighten me on this!

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