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# The Physics PHYA2 thread! 5th June 2013 Watch

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1. Do the waves of youngs double slit diffract as well as interfere ? Please explain
2. Perfect, thanks!
3. Can't wait to drop physics. Just praying tomorrow goes okay. Good luck everyone!
4. (Original post by x-Sophie-x)
For that question, could you possibly correct me if I'm wrong?

The ray hits the glass-air boundary at an angle of incidence of 50 degrees.

The ray is then totally internally reflected away from the normal and at the glass-water boundary, it again refracts away from the normal. TIR is 90 degrees right? So the angle of reflection would be 90-50=40 degrees?

At the water oil boundary, the ray refracts away from the normal through the glass container.
Isn't the angle 44?
And it refracts towards the normal before going through the glass container
5. (Original post by chrishy2012)
anyone have or know where i can find the January 2013 paper for physics. Really need it cause i missed my mock and thats the only paper i havent got at the moment!
Ill realllllyyyyy appreciate it
http://www.thestudentroom.co.uk/show...3#post42889460
6. (Original post by chrishy2012)
anyone have or know where i can find the January 2013 paper for physics. Really need it cause i missed my mock and thats the only paper i havent got at the moment!
Ill realllllyyyyy appreciate it
Here you go m8!
Attached Images
7. AQA-PHYA2-QP-Jan13.pdf (670.0 KB, 81 views)
8. AQA-PHYA2-W-MS-JAN13.pdf (182.1 KB, 88 views)
9. (Original post by Qari)
Isn't the angle 44?
And it refracts towards the normal before going through the glass container
Why would it be that?

I worked out theta to be 50 degrees, so using Z angles it's 50 degrees.
And there's a straight line so 180-(50+90) = 40.
And then you use that information to work out 50 degrees because the angles in the triangle there adds up to 180.

But of course, I don't really know what I'm talking about

I still don't understand why TIR happens in the first place
10. (Original post by x-Sophie-x)
For that question, could you possibly correct me if I'm wrong?

The ray hits the glass-air boundary at an angle of incidence of 50 degrees.

The ray is then totally internally reflected away from the normal and at the glass-water boundary, it again refracts away from the normal. TIR is 90 degrees right? So the angle of reflection would be 90-50=40 degrees?

At the water oil boundary, the ray refracts away from the normal through the glass container.
If the ray is TIR then how would it hit the glass-water boundary?
11. (Original post by StalkeR47)
Yes! A refracted ray has an angle less than or equal to the critical angle. When the incident angle is = to the critical angle, you will have an emergent ray parallel to the substance. But, increasing the incident angle bigger than to the critical angle(incident angle exceed the critical angle), total internal reflection occurs. Is that clear now m8?
Yeah cheers it I was just unsure. So if it asks you to refract a ray should you always draw a dotted line to show partial internal reflection incase you get a mark awarded for it?
12. (Original post by Anythingoo1)
You can refer to fringes as being dark (where the waves interfere destructively) or light (the opposite), maxima refers to just light fringes e.g. central maxima, first order maxima, etc

This is what you need to say:
When 2 similar waves travelling in opposite directions, they superpose to form a stationery wave. Nodes are formed when the 2 similar waves interfere destructively
Thanks. Also, I'm confused by the Jan 2012 Examiner Report for the last part of the last question - why does it say that "nodes are where the wave always cancels but the phase difference between the waves repeatedly varies from zero to two pi" and "are not always 180 degrees out phase in order to cancel at nodes"? How can the phase difference at a node vary from 0 to 2pi? I always thought it was always 180 degrees, but the examiner report says this is wrong, but I don't know why!
13. (Original post by x-Sophie-x)
Why would it be that?

I worked out theta to be 50 degrees, so using Z angles it's 50 degrees.
And there's a straight line so 180-(50+90) = 40.
And then you use that information to work out 50 degrees because the angles in the triangle there adds up to 180.

But of course, I don't really know what I'm talking about
Amm... do you know what time of the video is that example on?
14. (Original post by x-Sophie-x)
Why would it be that?

I worked out theta to be 50 degrees, so using Z angles it's 50 degrees.
And there's a straight line so 180-(50+90) = 40.
And then you use that information to work out 50 degrees because the angles in the triangle there adds up to 180.

But of course, I don't really know what I'm talking about
The refracted angle is 44, incident angle is 50. When you draw triangle inside glass you get 180- (90 + 44)=46 but angle to normal is 44. Using Z angle or two angles have to equal 90.
15. (Original post by Claree)
Thanks. Also, I'm confused by the Jan 2012 Examiner Report for the last part of the last question - why does it say that "nodes are where the wave always cancels but the phase difference between the waves repeatedly varies from zero to two pi" and "are not always 180 degrees out phase in order to cancel at nodes"? How can the phase difference at a node vary from 0 to 2pi? I always thought it was always 180 degrees, but the examiner report says this is wrong, but I don't know why!
phase difference is sort of the "time difference" between 2 points on a wave. For instance like you said, 180 degrees phase difference would be 2 points in antiphase, hence a node is formed, however, 2 points could have 90 degrees phase difference, or 270, or 345, etc. Any value between 0 and 360 (or 0 and 2pi if you like)
16. (Original post by BayHarborButcher)
Yeah cheers it I was just unsure. So if it asks you to refract a ray should you always draw a dotted line to show partial internal reflection incase you get a mark awarded for it?
I think it would not ask you to draw a refracted ray since you can always get it at a wrong angle. They will ask you to draw a TIR only. But, if they did ask you to draw a refracted ray, you will just have to guess according to the incident ray. Sometimes, they give you clues to workout how much of the ray is refracted.
17. Hey guys, if anyone could help me with this question I would be very very grateful. Cheers:

Diagram:

Question:

Info given: Refractive index of core is 1.47, RI of cladding is 1.45
Critical angle is 80.4 degrees

Thanks once again
18. (Original post by Qari)
The refracted angle is 44, incident angle is 50. When you draw triangle inside glass you get 180- (90 + 44)=46 but angle to normal is 44. Using Z angle or two angles have to equal 90.
I don't see why, because 44 is the angle of incidence of the first boundary and not the second??
19. (Original post by ccashman)
Do the waves of youngs double slit diffract as well as interfere ? Please explain
Yes they do as after the waves diffract at the first slit, and then diffract at the second slit, the two waves produced interfere with each other constructively and destructively producing a white fringe at the constructive interference and a dark fringe at the destructive interference.
Hope that helps.
20. (Original post by StalkeR47)
If the ray is TIR then how would it hit the glass-water boundary?
Is it not TIR at the glass-air boundary?
21. What do you think will come up tomorrow?
22. (Original post by x-Sophie-x)
Is it not TIR at the glass-air boundary?
Sorry Sophie. I am totally confused what you are trying to say. Do you know which exact question you need help with? Was the question on the video? If yes then at what time was it on?

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