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# The Physics PHYA2 thread! 5th June 2013 Watch

• View Poll Results: What mark do you think you got out of 70?
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1. (Original post by StalkeR47)
So, are you saying that all of the AS-level physics is worth 120 UMS in year 12? The unit 1 exam in June was the easiest past paper of my life What about you?
Yeah both exams are worth 120 ums and the ISA id worth 60. Yeah the unit 1 exam was pretty easy, do you know the last question, I didn't realise that they were in Kilo ohms, so do I lose all marks in that question or ecf for all questions after that because I got all the right answers but the prfixes were wrong?

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2. (Original post by Jimmy20002012)
Hey,

Thanks

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Basically:

The zero order beam is white (as all wavelengths just pass through).
Each other order is a spectrum, with violet on the inside and red on the outside.
3. (Original post by NedStark)
What do they mean by the single slit effect? Is that when a laser shines at a single slit causing diffraction?

Or is single slit the extra slit used in Young's double slit interference, just before the light shines through 2 slits?
'Without single slit effect' means the diffracted light that produces fringe pattern will have same intensity for all the fringes produces. Therefore, 'with single slit effect' would mean that all the fringes produces will have different intensity (middle to be the brightest).
4. (Original post by House MD)
Could you explain why this is the case? I'm not sure what you mean.
The difference between the distance of two waves is called the path difference. For example, consider that 1 wave has wavelength of 300nm and the other one has 100nm. The path difference will be 300-100 which is 200nm. If you are given the frequency of both waves, the wavelength found from that frequency would be the path difference between 2 waves. Is that ok?
5. For some reason, i always mess up mechanics questions and then when i go back over it i realise how simple it was!

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6. (Original post by Jimmy20002012)
Yeah both exams are worth 120 ums and the ISA id worth 60. Yeah the unit 1 exam was pretty easy, do you know the last question, I didn't realise that they were in Kilo ohms, so do I lose all marks in that question or ecf for all questions after that because I got all the right answers but the prfixes were wrong?

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Well.. That was the only question I got wrong. And the answer was 30k ohms. so if your answer was something like 30x10^3 ohms or 3.0x10^4 ohms, you will get the mark.
7. (Original post by Jimmy20002012)
Yeah both exams are worth 120 ums and the ISA id worth 60. Yeah the unit 1 exam was pretty easy, do you know the last question, I didn't realise that they were in Kilo ohms, so do I lose all marks in that question or ecf for all questions after that because I got all the right answers but the prfixes were wrong?

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Hey Jimmy! where has my thread gone? Physics Unit 2 As-Level PHAY2 Exam 05/06/13 exam discussion.
8. (Original post by StalkeR47)
Well.. That was the only question I got wrong. And the answer was 30k ohms. so if your answer was something like 30x10^3 ohms or 3.0x10^4 ohms, you will get the mark.
I got 30ohms only, soo stupid but I maybe will get ecf as they take into account the error of the prefix if you did it in the for the first question

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9. (Original post by StalkeR47)
'Without single slit effect' means the diffracted light that produces fringe pattern will have same intensity for all the fringes produces. Therefore, 'with single slit effect' would mean that all the fringes produces will have different intensity (middle to be the brightest).
I understand the intensity side of it but I'm confused on what equipment is being used to produce that graph without a single slit effect.

Surely if there is no slit at all, no diffraction occurs and there are no fringes since light just shines straight onto the screen.
10. (Original post by NedStark)
I understand the intensity side of it but I'm confused on what equipment is being used to produce that graph without a single slit effect.

Surely if there is no slit at all, no diffraction occurs and there are no fringes since light just shines straight onto the screen.
Oh nooooo! You got it all wrong. Basically, the red dotted curve is just shown to tell you the difference between using a single slit that is able to produce the interference pattern(the effect it has). But, for example, if you do not use a single slit(the effect without it), the intensity of the pattern produced (all the fringes) will be the same. I know the book is a bit dull about this thing and does not explains really well. Is that clear now?
11. (Original post by StalkeR47)
Oh nooooo! You got it all wrong. Basically, the red dotted curve is just shown to tell you the difference between using a single slit that is able to produce the interference pattern(the effect it has). But, for example, if you do not use a single slit(the effect without it), the intensity of the pattern produced (all the fringes) will be the same. I know the book is a bit dull about this thing and does not explains really well. Is that clear now?
But if a single slit is not used, then what is used instead? Doesn't no slit=no fringes?

12. (Original post by NedStark)
But if a single slit is not used, then what is used instead? Doesn't no slit=no fringes?

Correct! No slit=no fringe but the book is just trying to show you the difference between the effects of the single slit used. No problem!
13. (Original post by NedStark)
But if a single slit is not used, then what is used instead? Doesn't no slit=no fringes?

To be honest, I think that the red dotted curve should have been a straight like from the maximum intensity. Instead, they plotted it to be a fringe pattern shown with no single slit effect.
14. (Original post by StalkeR47)
Correct! No slit=no fringe but the book is just trying to show you the difference between the effects of the single slit used. No problem!
Thanks! now it's just made complete sense. You're right, if they just made one horizontal line then it'd be so much clearer.
15. (Original post by NedStark)
But if a single slit is not used, then what is used instead? Doesn't no slit=no fringes?

Also, notice that they say 'without single slit effect'. They do not say 'without single slit'. Get it?
16. (Original post by NedStark)
Thanks! now it's just made complete sense. You're right, if they just made one horizontal line then it'd be so much clearer.
No problem at all!
In the January 2009 paper question 6 (a ii if you care) there is a standard question asking you to draw the path of a light ray (classic)
The critical angle is 49degrees and the ray in question's incident angle is not labelled though clearly smaller than 49 degrees, the markscheme gives a marks for drawing partial internal reflection- why would partial internal reflection occur if the angle of incidence is smaller than critical angle? (By a fair bit) x
18. (Original post by Juliajuliajulia)
In the January 2009 paper question 6 (a ii if you care) there is a standard question asking you to draw the path of a light ray (classic)
The critical angle is 49degrees and the ray in question's incident angle is not labelled though clearly smaller than 49 degrees, the markscheme gives a marks for drawing partial internal reflection- why would partial internal reflection occur if the angle of incidence is smaller than critical angle? (By a fair bit) x
That paper was odd, no other paper really asked for that (I think), but generally there is always a partial internal reflection, even if it's refracted or exactly on the critical angle.

That's why is called Total Internal Reflection when it's greater than the critical angle, because partial internal reflection happens anyway. Recent papers haven't done this so I wouldn't bother but if you want to play safe then include it in the upcoming paper.
19. (Original post by Juliajuliajulia)
In the January 2009 paper question 6 (a ii if you care) there is a standard question asking you to draw the path of a light ray (classic)
The critical angle is 49degrees and the ray in question's incident angle is not labelled though clearly smaller than 49 degrees, the markscheme gives a marks for drawing partial internal reflection- why would partial internal reflection occur if the angle of incidence is smaller than critical angle? (By a fair bit) x
Hey! I am just helping everyone. I had my own thread where I was helping everyone but I am wondering that the thread has been lost. :P Anyways.....Q6aii) Since air has refractive index(n) of 1 which is smaller than the (n) of water. This means water has larger (n) than air. We have met 1 (TIR) statement of (n) but not the other which is, the angle of incident must exceed the critical angle. This is unknown since we do not know the angle of incident nor critical (and do not guess as it could be wrong). The diagram gives you a clue. If ray R is (TIR), ray Q is = critical angle, then what ray p should look like is obvious. Is that ok?
20. Hey, this is the paper I am dreading the most. I only need approx 40 out of 70 to get an A overall, but i am struggling to get there.

Anyone have any idea what might come up so I can go over it a bit. It's my only hope.

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