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# CCEA Physics AS2 Tweet

Physics exam discussion - share revision tips in preparation for GCSE, A Level and other physics exams and discuss how they went afterwards.

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1. Re: CCEA Physics AS2
(Original post by North Irelandman)
... Really want to see this question you're all talking about.
A wave was radiated towards 2 layers of ground (or rock or whatever), first layer A and 2nd layer B. It goes through layer A. We are told that it refracts, but it just reflects when the angle of incidence from A into B is 35 degrees, so therefore the critical angle is 35 degrees. Now, it gives you the equation that the speed of sound in A divided by the speed of sound in B or whatever it was, is equal to the refractive index from A to B. (aNb), and asks you to find speed in B. Usually you would use 1/sinC=n, however thats only if you're given the refractive index from air into the material. But this time, it told you that the refractive index was from A to B. Hence why I think the refractice index was just sin35 and not 1/sin35.
Last edited by CD315; 19-06-2012 at 17:23.
2. Ok so speed in A over speed in B is the refractive index from A to B... Speed in A was 5000 metres each second

Let's say for the purpose of making this more common to us that A is a glass block and B is the air...
So when 35 degrees TIR occurs but let's say that it refracts at 90 degrees along the medium of A to B for the sake of letting 35 be the critical angle... So aNb= sin 35/ sin 90 so aNb = sin 35

Then sin 35 will be equal to 5000/x

5000/sin 35 = x

X = 8717 ms^-1

You're right CD if that was how the question was worded If it was a sound wave however I'd be questioning if CCEA were right on this one... But if it was just a wave then you're certainly right by taking sin35

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3. Re: CCEA Physics AS2
It's one good question , my physics teacher said that in the department they where all debating what the answer was : D
4. Re: CCEA Physics AS2
Ok so speed in A over speed in B is the refractive index from A to B... Speed in A was 5000 metres each second

Let's say for the purpose of making this more common to us that A is a glass block and B is the air...
So when 35 degrees TIR occurs but let's say that it refracts at 90 degrees along the medium of A to B for the sake of letting 35 be the critical angle... So aNb= sin 35/ sin 90 so aNb = sin 35

Then sin 35 will be equal to 5000/x

5000/sin 35 = x

X = 8717 ms^-1

You're right CD if that was how the question was worded If it was a sound wave however I'd be questioning if CCEA were right on this one... But if it was just a wave then you're certainly right by taking sin35

This was posted from The Student Room's iPhone/iPad App
Hate physics haha.
5. Cheers, looks like CCEA had fun designing that question! Snell's Law was not taught well in my class last year so that would have been marks lost for a number of us. But yes, it would not have been 1/sinC, I would need to have a proper think but Fladam's solution makes sense to me. Definitely a good question to catch people out though, wouldn't worry too much about dropping a mark or two.
6. Was a very nice question for thinking through for sure! Caught me out in the exam, tried to rush it :P Generally snell's law isn't too bad so I wasn't expecting any tricks, well spotted CD! Should be fine, I would say Maybe a little bit of scaling on that paper too?

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7. Re: CCEA Physics AS2
Was a very nice question for thinking through for sure! Caught me out in the exam, tried to rush it :P Generally snell's law isn't too bad so I wasn't expecting any tricks, well spotted CD! Should be fine, I would say Maybe a little bit of scaling on that paper too?

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North Irelandman knows how much I love my scaling physics generally gets scaled up. I was hoping for at least 100/111 UMS there (90%) but I'm doubting it.
8. Re: CCEA Physics AS2
does anione know the grade boundaries for this?
9. Re: CCEA Physics AS2
(Original post by calender1994)
does anione know the grade boundaries for this?
No idea, but I got 66/75 which got scaled up to full UMS..
10. Re: CCEA Physics AS2
i got 106 so like 62 or there abouts then? and thanks for the reply
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