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# The Physics PHYA2 thread! 5th June 2013 Watch

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1. (Original post by x-Sophie-x)
Can anyone explain Question 7b in January 2011, please?
It's given you a clue The angle in the oil is the same as the angle in the glass
2. (Original post by x-Sophie-x)
Can anyone explain Question 7b in January 2011, please?
O sorry! You needed an explanation. And sorry, I gave you the wrong answer. I gave you the answer to 7e. For this, I would suggest you to watch this awesome video!!!!!http://www.youtube.com/watch?v=M5EW15BOy-c
3. (Original post by Jimmy20002012)
Apparently you don't use that in this question?

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I dont know the full question stem but if you have number of slits per mm you can find d and if you take n as 2 and you already have the angle you can use dSinTheta/n=lambda
4. (Original post by Qari)
What's the rule for refraction? Does it refract closer tot he normal if it goes into a lower refractive index or more?
Refraction is basically the bending of light.
If the ray goes from a material of a lower refractive index to a higher refractive index, it will bend TOWARDS the normal and vica versa.
5. (Original post by BajoLily)
Could someone please explain to me why, in the Jan 2013 paper - question 7bi, they used the speed of light when the question clearly states that they are microwaves?
Unless they've stated a different speed for the microwaves, you must always use:
6. (Original post by StalkeR47)
Why not Sophie? You will get TIR so just draw the same ray but TIR ray. Does that make sense? If not, I will post a diagram for you.
I'm a bit confused though, because I thought it's not totally internally reflected at the first boundary?
7. (Original post by BayHarborButcher)
Can someone explain to me when partial internal reflection happens? As in, on most of the questions you'd draw a refracted ray and that was it, full marks. But on just ONE of the questions one of the marks you get is for partial internal reflection?
Partial internal reflection happens when the incident angle is less than (<) or equal (=) to the critical angle. That is it.
8. (Original post by x-Sophie-x)
I'm a bit confused though, because I thought it's not totally internally reflected at the first boundary?
Oh sorry, I know. I gave you the answer to 7e instead of 7d. Check my previous posts above.
9. Currently sat wishing I had the motivation to revise for this :')

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10. Just checking:
For Youngs Slits (2 slits): Does the intensity decrease with distance from the central maxima? Or is that just for Single Slit diffraction? And what about the diffraction grating?

What would be the differences/similarities between the diffraction grating/youngs slits and single slit diffraction?

THANK YOU!
11. (Original post by StalkeR47)
Partial internal reflection happens when the incident angle is less than (<) or equal (=) to the critical angle. That is it.
But I dont understand, doesn't that mean it always happens as long as a ray is refracted? But this was the only question I've seen that asked you to show it.
12. (Original post by StalkeR47)
O sorry! You needed an explanation. And sorry, I gave you the wrong answer. I gave you the answer to 7e. For this, I would suggest you to watch this awesome video!!!!!http://www.youtube.com/watch?v=M5EW15BOy-c
Hahaha, no worries
And thanks shall watch it now
13. (Original post by Raimonduo)
Unless they've stated a different speed for the microwaves, you must always use:
Also they've stated it's in a vacuum
14. Guys this video is awesome!!!!http://www.youtube.com/watch?v=M5EW15BOy-c
15. (Original post by Qari)
What's the rule for refraction? Does it refract closer tot he normal if it goes into a lower refractive index or more?
A higher refractive index. When a light ray enters a substance which has a higher refractive index, than the incidence substance, it will refract TOWARDS THE NORMAL. Thus, the higher the refractive index of the substance, the more it refracts towards the normal.
16. Explanation for Jan 2013 q7 b(ii) please?
17. How does a node form? (with regards to phase/phase difference and cancellation)
18. What is the difference between a fringe and a Maxima in single slit diffraction?
19. Is it likely that hydroelectricity or water power will come up as I haven't seen it in any of the past papers yet?

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