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# The Physics PHYA2 thread! 5th June 2013 watch

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1. (Original post by StalkeR47)
Incident substance is the core.
there you go core (refractive index of 1.47) cladding (refractive index of 1.45) angle of incidence does not exceed critical angle therefore NO T.I.R. if angle of incidence does exceeds critical angle then you DO GET T.I.R.

however IF angle of incidence does exceeds critical angle but core (refractive index of 1.45) cladding (refractive index of 1.47) then you will get refraction since core is optically less dense than the cladding.
2. (Original post by StalkeR47)
Alright then! sini(critical)=n2/n1. n2 is 1.45 and n1 is 1.55. critical angle is therefore 69.3 deg. So, 1 (criteria) is met and the other isn't. Then, why refraction and not reflection.?
What's the definition of critical angle?

And again one critieria is met but the 2nd one isn't. Meaning you need to meet both criteria's
3. (Original post by Qari)
Do you have to show that? And wouldn't it be based on wavelengths?
Show what?

Well there are blue inner fringes and red outer fringes, so yes its based on wavelengths.
4. (Original post by masryboy94)
there you go core (refractive index of 1.47) cladding (refractive index of 1.45) angle of incidence does not exceed critical angle therefore NO T.I.R. if angle of incidence does exceeds critical angle then you DO GET T.I.R. however if angle of incidence does exceeds critical angle but core (refractive index of 1.45) cladding (refractive index of 1.47) then you will get refraction since core is optically less dense than the cladding.
Sorry, you are mistaken there. Cladding has refractive index of 1.45 not 1.47. So, core is more dense than cladding.
5. (Original post by lebron_23)
You would just show the screen how you would see it if you were looking at it. Meaning you would just draw a rectangle/square/your favourite shape and show the maxima as either the same width or half the width of the central maxima (depending on whether its double slit or single).

As for indicating the violet colour near to the central maxima, you would just label it saying something like 'the maxima closer to the central maxima have a violet tinge while the maxima further away take on an increasingly darker red tinge'.

Yeah tell me about it! On average, you can drop 9 marks and still walk away with full UMS. Seems like a golden opportunity but I just know I'm going to throw away marks somewhere tomorrow
wait, I thought each maxima would contain all the colours of the white light spectrum with violet/blue on the inner side closer to the centre and red on the outer side

you seem to suggest that a maxima would contain only one colour (or mainly one colour), or have I misinterpreted you?
6. (Original post by masryboy94)
there you go core (refractive index of 1.47) cladding (refractive index of 1.45) angle of incidence does not exceed critical angle therefore NO T.I.R. if angle of incidence does exceeds critical angle then you DO GET T.I.R. however if angle of incidence does exceeds critical angle but core (refractive index of 1.45) cladding (refractive index of 1.47) then you will get refraction since core is optically less dense than the cladding.
Core is 1.55 and cladding is 1.45. Core is more dense.
7. Hey, Can anyone help me with January 2013 question 7b(ii), 7(c) and 7(e) ??
thanks
8. (Original post by StalkeR47)
Sorry, you are mistaken there. Cladding has refractive index of 1.45 not 1.47. So, core is more dense than cladding.
omg lool im giving you an example of when IF​ cladding is greater than core and when core is greater than cladding
9. (Original post by sceezy)
Hey, Can anyone help me with January 2013 question 7b(ii), 7(c) and 7(e) ??
thanks
B(ii) you count the waves.
10. (Original post by masryboy94)
omg lool im giving you an example of when IF​ cladding is greater than core and when core is greater than cladding
Alright man. Anyway, I will just have to stick to the rules. Does not matter about the reason why. Thanks for your help.
11. (Original post by Jack93o)
does anyone understand wavelets and how the waves passing through a single slit actually manages to interfere with itself to create minimas?
Don't think that is actually on the spec for A level (i.e explaining why it happens) from my memory of doing this exam but you can always do some research.
12. (Original post by StalkeR47)
No! All I was saying that why TIR does not occur if incident substance has larger refractive index than the other? Can you answer this? HUH? same question.
No that really isn't what you were saying. Your reasoning alluded to TIR being possible if only a single criteria was met.
Proofs:

13. Ideally, should the cladding be more refractive or less refractive than the core?

I'm guessing less refractive so TIR occurs?
14. (Original post by Jack93o)
wait, I thought each maxima would contain all the colours of the white light spectrum with violet/blue on the inner side closer to the centre and red on the outer side

you seem to suggest that a maxima would contain only one colour (or mainly one colour), or have I misinterpreted you?
You're right, sorry I should have made myself clearer. The maxima do indeed contain all of the colours from white light (only in the case where white light is used), but they just pick up a red tinge the further away they get from the central maxima. Apologies for any confusion caused there.

However, do remember that each maxima will only contain all the colours of the spectrum if white light is used. If, for example, a laser light is used (red light), then all of the maxima will take on a red hue/tinge/colour.
15. (Original post by NabRoh)
No that really isn't what you were saying. Your reasoning alluded to TIR being possible if only a single criteria was met.
Proofs:

That's what I thought, but it doesn't really matter.

He either got confused, (and I don't blame him) or his response wasn't what he was actually trying to say. Either way, we know now
16. (Original post by x-Sophie-x)
Ideally, should the cladding be more refractive or less refractive than the core?

I'm guessing less refractive so TIR occurs?
the cladding should have a lower refractive index than the core or TIR will not occur
17. (Original post by NabRoh)
No that really isn't what you were saying. Your reasoning alluded to TIR being possible if only a single criteria was met.
Proofs:

Yeah I know. I knew it was something like this but I was not 100% sure since I do not have the best memory.
18. (Original post by x-Sophie-x)
Ideally, should the cladding be more refractive or less refractive than the core?

I'm guessing less refractive so TIR occurs?
YEP
the cladding should have a lower refractive index than the core or TIR will not occur
Thank you
20. (Original post by StalkeR47)
Alright man. Anyway, I will just have to stick to the rules. Does not matter about the reason why. Thanks for your help.
haha no worries bro, its good we had this discussion, it actually made me think and be sure hope you get it now though p.s. you look like a 120 UMS boy you know your info my man, its just abit of confusion we all get so dw

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